[Steam, Hot-Water and Gas Distribution Systems]
[From the U.S. Government Publishing Office, www.gpo.gov]

NA/ L	NON-CIRCULATING
Document	FA Fl _____I /STA a____J — HEAT BALANCER
OUR WIRES IN CABLES (LOW VOLTAGE)
(5)	Type of construction.
(6)	Expansion and contraction.
(7)	Drainage.
(8)	Venting.
(9)	Protection against excessive pressures.
b.	These 1 actors are more or less interrelated and must be considered from the standpoint of initial, operating, and maintenance costs if the system is to meet requirements at the lowest over-all cost.
5.	Materials
Materials commonly used are cast iron, wi ought iron, steel, brass or bronze, and copper. Cast iron is used foi valves, fittings, ells, tees, flanges, and traps in low pressure systems because of its low cost and
resistance to corrosion. It is also used for pipe in certain special applications. Wrought iron is sometimes used for pipe, but its use is decreasing because of its higher cost. Its use may be justified in cases where steel pipe is rapidly destroyed by corrosion. Steel is used almost universally for the pipe because of its low cost, ease of fabrication, and high structural strength. Brass or bronze is used for small valves for pressures up to 250 psi and for trimmings (seats, bushings, stems) on larger valves because it resists corrosion and is easy to manufacture. Brass pipe can also be used, but its high cost reduces its use to a few specialized applications. Copper tubing and pipe are also expensive, but lower installation cost and higher resistance to corrosion may make them more economical than iron or steel pipe.
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6.	Size
a.	Steam Lines. The size of the steam lines depends on—
(1)	Amount of steam to be used.
(2)	Pressure of the steam.
(3)	Pressure drop or difference available for forcing the steam to flow.
b.	Water Lines. For water lines, the size depends on—
(1)	Amount of water to be handled.
(2)	Pressure drop or difference available for causing the flow.
7.	Pressure and Temperature
The pressure to be used depends on maximum temperature required, size of the line, and distance the steam is to be transmitted. In some cases the pressure is determined by the equipment available to generate the steam. In Army practice, steam is usually supplied to laundry machines at 100 psi, to hospital, cooking, and sterilizing equipment at 40 psi. and to building heating systems at 5 psi. Steam is generated
at pressures slightly higher than 100 psi to allow for pressure drop in high-pressure lines. Lower pressures are obtained by use of pressure-reducing valves. A typical Army installation is shown schematically in figure 2. Steam is supplied at pressures of 100 psi and 40 psi to the laundries and hospitals, respectively, because of the temperatures required to do the job for which the steam is used. The temperature of saturated steam is directly related to its pressure. This is not true with superheated steam, which is rarely used in heating systems. This relationship is shown in table I.
Table I. Rerationship betzveen saturated steam pressures and temperatures
Pressure (psi)		Temperature (°F)
r Gage	."-solute *	
100	115	338
40	55	287
5	20	228
* Figures in this column are obtained by adding to gage pressure the 15-psi assumed value of atmospheric pressure. Since atmospheric pressure varies, this method is not always exact but is sufficiently accurate for ordinary purposes.
STEAM FROM BOILER PLANT. PRESSURE 100 PSI
*---40 PSI	_________(5
GO
. Q	——100 PSI	■*-----5 PSI
TO ATMOSPHERE	Q
I	HOSPITAL — 5 PSI	LAUNDRY	BARRACKS
11	T pr~| F-M [■pi
TO HEATING *2 r£P—’	----*-0|
SYSTEM	z o	---- -j—.
I—I—*	“ LE	H
O = T R	’---I—*-0-1
w 5 pi	LEGEND:
£ "Lr-1	Hl
—I______ LLI	----- H	T
L LE	LLqj_	GATE VALVE
FLASH	0}	zp
•tank-----------------------------------------------*----------------(5 RELIEF VALVE
PRESSURE-A REDUCING V VALVE 0
I_________________S ----------------------------3--------------- 0 TRAP
J RETURN TO	[	. RETURN TO	|~|
* boiler plant	boiler plant	□ HEATER
■*-RETURN TANK 
LAUNDRY
3Lt EQUIPMENT
-------------------------PUMP	---- BOILER FLAN I
Figure 2. Schematic diagram of steam system for Army installations.
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8.	Hartford Loop
A Hartford loop is used in most gravity return systems to give warning of low water. It is formed by arranging a vertical loop in the return line. The top of this loop is at the lowest safe level of water in the boiler. The top of the loop is also connected to the steam line. If the water is allowed to drop this arrangement causes water hammer, thus calling attention to the condition. The Hartford loop is also used on other low-pressure heating systems.
Section II. CONSTRUCTION DETAILS AND EQUIPMENT
9.	General
Construction used by the Army is either underground or above ground. In underground construction, the lines are installed in ducts or a tunnel with proper supports, to protect lines from mechanical injury and external corrosion. W hen above ground, lines are supported overhead from a steel or wood framework or by small piers usually made of concrete. Provision is made for sufficient expansion to prevent damage to the equipment or supporting structure. The amount of expansion to be provided depends on the size of the equipment and on the difference between the highest and lowest temperature to which it is subjected. In the case of a pipe line, size refers to the length of the pipe. Several methods are used to compensate for expansion in a pipe line: one is to erect the line with enough bends so expansion can be absorbed l.y bending of the pipe; a second method is to use special expansion bends or loops in the line; a third, to erect the line so a change in length will cause the pipe to screw into or out of some of the fittings; and a fourth, to use expansion joints. The third method is applicable only to screwed connections ; it is not recommended for general use because it causes wear in the joints and makes it difficult to keep them leaktight.
10.	Drainage
The water which results from steam condensing in the line must be removed to prevent water hammer in the lines and to permit operation of heating equipment at rated capacity. In underground ducts, provision must also be made to dram ground water away from the duct to prevent the possibility of water leaking in and damaging insulation or pipe. Internal drainage is usually accomplished by giving a little slope or pitch to the lines and by collecting the moisture in drip pockets at low points of the
line. Water is removed from drip pockets by traps which permit the flow of water but prevent discharge of steam. Underground lines are drained externallv by placing porous material such as gravel around or under the duct, or drain tile under the duct.
11.	Vents
Air must be removed from the system or it will blanket the equipment and prevent it from functioning. Air enters the system when it is shut down or when pressure is removed; air may also be dissolved in the water fed to the boilers. Air can be removed automatically by certain types of traps or manually by operating valves installed at the proper locations.
12.	Protection
A distribution system is protected against excessive pressures by safety or relief valves which open at a definite pressure and permit steam to escape, thus lowering the pressure.
13.	Piping
a.	Size. The size of steel pipe is stated in nominal inside diameter up to and including 12-inch pipe. Above 12 inches, the size is based on outside diameter and is known as OD pipe. The grades of steel pipe in general use are standard, extra-heavy, and double extra-heavy, d he weight of pipe to be used is governed by the pressure which it must stand.
b.	Construction. Pipe can be made by forming a piece of strip steel into a cylinder and welding the two sides of the strip together. A lap or butt weld is used and both operations, forming and welding, are performed at the same time. A close examination of a small pipe will usually show the line of the weld. Pipe can also be made by piercing and rolling a solid rod or billet while it is very hot. Pipe made in this manner is called seamless pipe-size tubing; it is a superior and more expensive product.
c.	Assembly. Pipe may be assembled with threaded or welded joints. The standard system of pipe threads used is the Briggs, in which the thread has a taper of inch per foot, thus making it possible to obtain a tight joint when screwing the pipe into a fitting. The pipe may be made with screwed or flanged fittings. \\ hen flanged fittings are used, the pipe is screwed in a flange before erection. The use of screwed fittings makes it difficult to remove some sections ot line, and it is difficult to erect and tighten the joints of larger sizes. A fitting called a union is used to provide a means of disconnecting a pipe line, and for the final or closing fitting of a run. Unions
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are also used when connecting equipment such as traps, heaters, radiators, and pumps, and are sometimes placed on both sides of the equipment to permit its easy removal without dismantling any of the pipe system. Flanged or welded construction is used on lines over 4 inches in size. Flanged construction permits removal of any section of pipe or fitting for inspection or repair without disturbing any other part; however, gaskets must be used, and sometimes cause trouble because of leakage or blow-out. Welded construction, which is coming into more common use, is faster, contains no joints to leak and cause trouble, has no projections to interfere with covering, and requires less material for an overall system. The disadvantage of welded construction is that it cannot be dismantled for inspection or repair and then be reassembled, without the services of a welder.
14.	Insulation
I he piping of a steam distribution system is covered with an insulating material to reduce the amount of heat lost from the line. In some cases the insulation must be covered to protect it from mechanical injury or moisture. All heat insulating materials arc poor heat conductors. Air conveys heat readily if permitted to circulate, but it is a very poor conductor of heat when held motionless. An insulating material in common use, called 85 percent magnesia, is a mixture of magnesium carbonate and asbestos fibers; while these two materials are poor conductors of heat, they conduct heat about three times as readily as air. Insulation using these two materials is manufactured in such a way that air is included in very small volumes and is prevented from moving or circulating. An insulating material, to be successful, must be capable not only of preventing the loss of heat, but also of withstanding the effects of vibration and high temperature, and of retaining its insulating qualities throughout a period of years.
a.	Above Ground Pipe Insulation. Aboveground insulation must be protected from moisture which reduces its usefulness and shortens its life. Indoor insulation may be protected to a certain extent by wrapping it with canvas, and then painting the canvas. Outdoor insulation is protected from the weather by wrapping the covering with an asphalt-impregnated paper or burlap, then painting the line with an asphalt paint to seal the crevices. When it is necessary to protect insulation from mechanical injury, it is wrapped with a light-gage sheet metal. The thickness of insulation to be applied, or whether any should be used, is based on the saving which can
be made. The installed cost of insulation should be paid for in fuel savings in a relatively short time. As the thickness of a given insulating material is increased, the heat loss through it decreases. However, beyond a certain thickness, the saving will not offset the increase in cost. Several charts and other information on the most economical thicknesses for various conditions are published in the handbook of the National District Heating Association, Greenville, Ohio. Thicknesses recommended by reliable manufacturers are usually satisfactory.
b.	Lnderground Pipe Insulation. Many variables affect the usefulness of insulation material for underground service. Pipes in tunnels are covered with sectional insulation of conventional types covered with a waterproof jacket. Conduit systems which may be of several types, sizes, or shapes, are more common than tunnels. Conduits are often a protective structure, and in addition provide a waterproof cover for the insulating material. Pipes carried in conduits may be covered with sectional insulation, or the entire space around the pipe may be filled with loose, dry insulating material. There are also materials which are mixed and cast in place like concrete. In all cases insulation must be kept dry, and waterproof coverings must be used. A drainage system below the pipe is sometimes necessary.
15.	Hangers and Supports
Pipe lines must be supported to guard against excessive stresses in the fittings and to prevent sag of the line as a result of its dead weight, expansion, and vibrations. Supports are also installed to guide the movement of the pipe in certain locations and to prevent thrust forces from being exerted on certain equipment. The pipe may be supported from above by various types of hangers. These hangers may consist of perforated steel strip, one end of which is fastened to the pipe and the other end nailed or bolted to the supporting framework. Another type consists of a band around the pipe and two steel rods connected by a turnbuckle. One end of the rod is fastened to the supporting framework and the other to the pipe band. The turnbuckle is used to adjust the length of the hanger. Any one of several types of spring supports or a counterweight arm may also be used. All these hangers permit movement of the pipe sidewise and lengthwise. Several hangers, properly arranged, may be used at one location to prevent sidewise movement or swaying of the pipe. The pipe may also be supported from below by brackets fastened to the supporting framework. These brackets
may be macle with rollers on which the pipe lays and which permits lengthwise movement but restrain sidewise movement.
16.	Anchors
Anchors are supports which are fastened rigidly to the pipe to prevent its movement. They are used to locate a given section of the pipe positively and to control the direction to the pipe expansion. Anchors are often used near the boilers to prevent thrust on the steam outlet, or where branch lines leave the main line.
17.	Expansion Joints
Because of limitations of the supports, or the space or extra length of pipe required, it is sometimes inconvenient to compensate for expansion of a line with the special bends and loops made for this purpose. As an alternative, expansion joints may be used. Two general types of joints are in common use; they are ordinarily classed as the slip and the bellows joints. The number of expansion joints installed in a line depends on the amount and direction of expansion and the amount of expansion permitted by each joint.
a.	Slip Type Expansion Joint. The -slip type expansion joint consists of an outer casing or body which is anchored, a sliding tube which fits into the body, and a means of preventing leakage between the inner and outer sections. An example of this
type of joint is shown in figure 3. This is an example of a double joint in which a plastic type of packing is used. The plungers (fig. 3©) are backed out, packing is forced in with a pressure gun similar to that used for greasing automobiles, and the plungers are then screwed down. This joint may be applied with welded or flanged construction. Several types of similar joints use ordinary braid packing adjusted by means of a gland. They may be either the outside guided type or inside guided joints. The pipe line must be held in alinement if this type of joint is to function properly. Expansion or contraction moves the inner sleeve in the main anchored casing or body. Stops must be provided in these joints to prevent their pulling apart.
b.	Bellows Type Expansion Joint. The expansion in the bellows type of joint is taken care of by the flexing of a metal bellows. When installed in the line, the joint consists of a corrugated thin-walled copper tube which is clamped between the flanges. (See fig. 4.) The rings help to keep the corrugations in the joint under high pressures. This joint does not usually have a safety stop. Another type of joint (fig. 5) uses a stainless steel multidisk bellows. This joint has an internal sleeve which acts as a stop to. limit the flexing of the disks and to limit the maximum flow of steam through the bellows if the disks rupture. Both these joints can compensate for a small amount of misalinement, but the pipe should be supported and guided in such a way that mis-
® Double-end welded type joint.
Figure 3. Slip type expansion joint with plastic packing.
1
I I 1P I
/ /	\ -J?// //	/7/k DEFLECTO:* VANE	_• J
K>  V ==ft\\\A	LE=^iJ
UiBg m I
GASKET	^• \<> 'A- .	PLASTIC PACKING
CCvAxCxCvLxLxVxC'xCx sleeve A \\ '. '\V\ \X\Lx\\\X
L---------------------------	DEFLECTOR VANE ----------------
@ Details of joints.
Figure 3.—Continued.
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alinement is reduced to a minimum. It is best that misalinement be prevented altogether if possible.
18. Valves
Valves are used to control the amount of steam flowing, to stop the flow altogether, to prevent excess pressures, and to prevent flow in the wrong direction.
a. Stop Valves. Stop valves are used to stop or throttle the flow. The gate, globe, angle, plug-cock, and stop-and-check valves are common types.
Figure 4. Corrugated bellows type expansion -valve.
(1)	Gate valves. A gate valve consists essentially of a body and a disk which slides across the flow path and shuts it off. It is used in all cases where a valve is to be kept wide open, as it creates very little disturbance in the flow. It should be used also in positions where the valve normally is to remain tightly closed. It must not be used for throttling-purposes; because the seats cut out rapidly and are difficult to keep in repair. These valves are made entirely of brass in the smaller sizes and for lower pressures. In the larger sizes the body and bonnet are cast iron, and the wedge disk, seats (which are replaceable), and spindle are brass or bronze for pressures up to 250 psi. The spindle shown in figure 6 is a rising type; when the valve is open the spindle rises and it is easy to tell whether the valve is in the open or closed position. On some valves of this type, the spindle screws into the wedge as the wedge is
opened, and it is not apparent whether the valve is open or closed.
(2)	Globe valve. The small, low-pressure globe valve in figure 7 has renewable metal seats. This type of valve is used where it is necessary to throttle the rate of flow. It must not be used otherwise because of the disturbance it creates in the flow of fluid. This valve is placed in a horizontal steam line with the Stem horizontal to prevent collection of water in the valve and line. When the valve is closed, the pressure must always be beneath the seat. I he disks in smaller valves may be any one of a number of materials; otherwise, the valves are made of the same materials as the gate valves. 1 hus, for cold water, hard-rubber composition gives good results; for hot water and low-pressure steam, babbitt; and for high-pressure saturated steam, copper or bronze. Figure 8 is a packless type used in heating service in which a sylphon bellows encloses the stem, eliminating the need for packing.
(3)	Angle valve. An angle valve is one in which the fluid leaves at an angle of 90° with the direction li om which it enters. It is usually constructed with the same type of seat and disk as the globe valve.
_ (4) Plug-cock valve. A plug-cock valve consists of a body with a tapered hole at right angles to the pipe connections. A tapered plug with a hole or slot at right angles through it fits into the hole in the body. The plug is equipped with a wrench or handle which operates through an angle of 90°. The valve is kept either wide open or closed because it is difficult to keep tight if used for throttling.
(5) Stop-and-check valve. A stop-and-check valve consists of a stop valve and a check valve made in one body, arranged to function as separate and distinct valves. The nonreturn valve used on boilers is sometimes incorrectly referred to as a stop-and-check.
b. Check Valves. A check valve operates automatically to prevent reversal of flow of the fluid. Two types of check valves are shown in figures 9 and 10. Fluid enters below the seat and lifts it, permitting the fluid to flow. The weight of the seat closes it as soon as flow ceases. These valves sometimes slam when they close. Usually, this occurs when the valve sticks open, permitting the flow to reverse and leach a comparatively high velocity before the valve closes: as a result, it slams shut and causes considerable shock in the pipe line. The lift-check type causes more disturbance to the flow than does the swing-check valve. The lift-check valve also tends to spin when open, thus resulting in wear on the piston, guide, and seat.
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STAINLESS STEEL MULTI DISK BELLOWS
COMPRESSION LIMIT
Figure 5. Multidisk bellows type expansion valve.
c. Relief Valves. Relief valves (fig. 11) protect pressure vessels or lines from overpressure. Popsafety valves used on steam boilers are seldom used in steam distribution systems. Relief valves can be used with liquids or gases, including steam, on installations not covered by code requirements. Unlike safety valves, relief valves do not start to open at the set pressure; they require about 20 percent overpressure to open wide. As the pressure drops, the valve starts to close and shuts off at approximately the set pressure. These valves are brass or bronze
in the smaller sizes and cast iron and bronze in the larger sizes.
d. Blowoff Valves. Valves constructed specifically for blowoff service are used on steam boilers. They are designed with special provision for passing sludge and scale without interference with the requirements of tight seating. Wearing parts are easily accessible and replaceable. They are comparatively expensive and their use is limited to the boiler. Other valves installed on distribution system equipment for drainage and cleaning of tanks, receivers, or drip
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FORGED STEEL FLANGES---
---EXTERNAL SLEEVE
--ANCHOR BASE
EXTENSION
LIMIT
\ LIMIT
STOP
INTERNAL^ SAFETY SLEEVE 1
Figure 6. Rising-stem gate valve.
legs, need not be of special construction; however, valves which permit a straight-through blow must be used. Plug cocks are well adapted to this use.
c. Pressure Regulators. Where high-pressure steam is supplied and lower pressures are required for space heating, water heating, or other services, pressure-reducing regulators are used. These regulators are essentially valves in which the seating disk
Figure 7. Globe valve with renewable metallic seat and disk.
is positioned automatically to maintain a set pressure on the downstream or low-pressure side. Power to position the valve comes from a diaphragm actuated by a connection to the low-pressure line. Adjustment is obtained by opposing part of the diaphragm thrust by an adjustable spring or a weight-and-lever arrangement. General features of these regulators arc shown in figures 12, 13, and 14.
(1) Single- and double-seated valves. Single- and double-seated regulators are used in two general classes of service. Single-seated valves (fig. 12) are used to shut steam off tightly and to prevent pressure from building up on the low-pressure side during no load periods. When low-pressure lines and equipment condense enough steam to offset some leakage, the double-seated or balanced type of valve (fig. 13) may be used. These valves require a smaller diaphragm for operation and will control the low pres-
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BUILT UP BELLOW-TYPE EXPANSION MEMBER WITH COMPOSITION VALVE DISK
LEAKPROOF, PACKLESS CONSTRUCTION
REGULATING PLATE
Figure 8. Packless radiator globe valve.
ROUNDED SEAT
Figure 9. Check valve, lift-check type.
12
Figure 10, Check valve, $wing*check type.
SPECIAL HEAT RESISTING HANDLE
Figure 11. Relief valve.
sure more closely under conditions of fluctuating high pressure.
(2) One- and tzvo-stagc reduction. When initial steam pressure is 100 psi or greater and the low pressure required is 5 psi or less, it is common practice to install two-stage reduction. This type of installation reduces noise and cuts down wear on the valve seats, since large valve openings are possible.
Figure 12. Single-seat pressure regulator.
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Figure 13. Double-seat pressure regulator.
PRESSUREREGULATING
SPRING----
DIAPHRAGM-
PILOT VALVE-
STRAINER----
SUPPLY PRESSURE
— OPERATING PISTON
-MAIN VALVE
--PRESSUREADJUSTING
SCREW
—<—-...--i- ..
Figure 14. Pilot-operated pressure regulator.
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If one-stage reduction is desired, a pilot-controlled single-seated valve (fig. 14) will usually prove satisfactory. If the pilot type cannot be used, two-stage reduction is necessary since the plain-diaphragm valve would require a diaphragm area which would be impractical. In making a two-stage reduction, allowance for increased volume of steam is made by increasing the pipe size on the low-pressure side. Separating the two valves by a distance up to 20 feet is recommended to reduce excessive hunting action of the first valve. Spring-loaded valves are usual if the reduced pressure is greater than 15 psi. Below this figure, the weight and lever type gives good results.
(3) Sizing of regulators. Many of the troubles encountered with regulators are directly traceable to improper size. A common error is making the reducing valve the same size as the connecting piping. Generally this practice results in the valve being oversize and causes wire-drawing of the seat parts because of the small lift necessary to pass the required steam. Therefore, the probable steam flow must be determined and the valve rated to pass this amount selected. With large installations the seasonal variation may result in damaged valves because of wire-drawing when weather is mild. To overcome this difficulty, two reducing valves are installed in parallel. These are selected with capacities of about 70 and 30 percent of maximum requirement. The larger valve is set to control at the normal demand and normal pressure, the smaller one at a slightly lower pressure. During mild or reduced-demand periods, steam flows through the smaller valve only as the larger one is set so that it will not pass steam at the pressure resulting from the reduced demand. During the remainder of the season the larger valve controls the steam flow. Thus, when steam flow is near its normal demand the larger valve is open, but the smaller is closed. The smaller valve remains closed by reason of the pressure maintained in the system. When the demand exceeds capacity of the large valve, the resulting pressure drop brings the small valve into operation and the two valves remain open until the pressure builds up sufficiently to close the smaller valve.
(4) Installation. Proper installation of reducing valves requires careful attention and planning. These units require servicing and repair at intervals. Ready access for this service is highly important. Normally, reducing valves are installed with the diaphragm down; this is not true except for pilot-operated valves. A bypass one-half the capacity of the reducing valve is required at the regulating station. This line
must have a high-grade globe valve which is able to shut off flow completely. Strainers are always needed on the inlet side of the regulator except in a second-stage reduction. Pressure gage and relief valve are installed on the low-pressure line.
f. Control Valves. A control valve may be any type of valve used to control flow. When service requires a valve to be either fully open or fully closed, gate valves (a(1) above) are recommended. Straight or angle globe valves, preferably with renewable seat and disk are suitable for throttling service. They are commonly used in such locations as bypass lines around reducing valves, traps, and feed-water regulators, and in places where similar service is required.
19. Traps
A steam trap is a device to drain water from a steam pipe, separator, radiator, kettle, or sterilizer without allowing steam to escape. The trap is an important piece of equipment, for if the water is not removed, the associated apparatus will not heat. If steam is permitted to blow through the trap, heat is lost. The •common difficulties experienced with traps are: cut seats caused by throttling the flow, air binding, stoppage by foreign material, and worn pins or bearings. Seats of a float trap are more liable to be cut than those of the intermittent discharge type; this is particularly true for float traps operating at low flows. Seats which are badly cut or worn permit the loss of steam. A trap which is airbound is inoperative. Worn bearings and pins may cause the trap to stick and make it inoperative. Traps may be classified according to operation as thermostatic, float, bucket, impulse, and throttling traps.
a.	Thermostatic Trap. Thermostatic traps (fig. 15) are widely used on radiators. The sylphon bellows contains a fluid which expands and vaporizes when heated. This action builds up a pressure inside the bellows, causing it to elongate and close the valve. When water collects around the sylphon and cools slightly, the sylphon contracts, opening the valve and letting water escape. As water is forced out, steam conies into contact with the bellows, causing it to close the valve thus preventing the escape of steam. The sylphon and the lower valve seat can be removed from the trap without disturbing any of the pipework.
b.	Float Trap. A float trap (fig. 16) is a combination float and thermostatic trap. The thermostatic trap normally vents the air, but it can also discharge water if the capacity of the float valve is exceeded. Water enters the trap and raises the float, carrying the vertical valve with it, This action opens
15
Figure 15. Thermostatic trap.
the valve and permits the water to discharge; as the water level in the chamber drops, the float gradually drops and closes the valve. Normally, with a constant flow of condensate to the trap, the level of water in the trap is stable and the trap discharges water continuously at the same rate as the condensate enters. At low rates of flow the level of water in the trap is low and throttling of the discharge causes the seats to cut badly, a disadvantage characteristic of this type of trap. The thermostatic trap in the top of the chamber remains closed as long as there is steam around it. This trap can be opened for inspection or repair without disturbing any pipe connections.
c. Bucket Traps. Bucket traps get their names from the fact that the operating element is a small bucket, The trap may be made with the open end of the bucket at the top or bottom. When the open end of the bucket is at the top, the device is called a bucket trap; when the open end is at the bottom it is called an inverted trap.
(1) Inverted bucket traps. Figure 17 shows an inverted bucket trap in the closed position with water
Figure 16. Float trap.
entering the trap under the bucket. The steam under the bucket slowly condenses and permits water to fill the bucket until it sinks, opening the valve (fig. 18) and discharging the water. After all the water is removed from the inlet line, steam discharges into the trap under the bucket, and collects under the bucket, forcing the water out and causing the bucket to rise and close the valve. As can be seen, the trap discharges only to the level of the valve, thus leaving the trap immersed at all times. To prevent the trap from becoming airbound, the trap is provided with an air-vent hole. I his trap can be disassembled for inspection and repair without disturbing the piping.
. El1----------------........
OUTLET —T '—
H&C	'water
____irr-’'*-1-' —■ —	in pot
AIR I-	*
BUBBLES-b-ng
STEAM
—J WATER
haw ,N
VENT HOLE —^^ggJF	~T	FLOAT
—)NLET
Figure 17. Inverted bucket trap with trap closed.
(2) Bucket trap. Figures 19, 20, and 21 show construction and operation of a bucket trap. Condensate and steam enter the body of the trap (fig. 19) in which an empty bucket floats. The water flows over the edge of the bucket and starts to fill it. When
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— INLE7
-OUTLET
, i-'*	..J2L
OUTLET ["*" |f% J_	1
|7B
WATER '	7
DISCHARGING	J"™
ggjjjgfe.;
"f INLET '
Figure 77. Inverted bucket trap discharging water.
enough water has entered the bucket sinks, allowing the water to be forced out. (See fig. 20.) When enough water has been forced out, the bucket rises closing the valve and leaving the column from the bucket bottom to the valve full of water. If air is present, it is drawn into the column as in figure 21, and the water in the column drops into the bucket as in figure 19. The air is discharged the next time the valve opens.
Figure 20. Bucket trap discharging water.
/ VALVE
OUTLET	■pJMEZBL' _I	INLET
I "------- —W* Rt |u	,
ill
—a I I
B|g FLOATING BUCKET
B ---PLUNGER
AIR VENT —I*
3 c B o g| g " 2a i-
■ ■ MOVABLE ARmWJSHSE
Figure 21. Bucket trap after discharging water.
Figure 19. Bucket trap with trap closed.
17
d. Impulse Trap. Operation of impulse traps (fig. 22) depends on the fact that a certain amount of hot water will flash into steam when the pressure exerted on it is reduced. The traps operate with a moving valve impelled by changes in pressure in a control chamber. The valve has a tiny orifice drilled through its center which allows continuous bypassing from the inlet to the control chamber. This flow reduces the chamber pressure below the inlet pressure and the valve opens, allowing free discharge of condensate. As the remaining condensate approaches steam temperature, flashing results; flow through the valve orifice is choked and pressure builds up in the control chamber, closing the valve. About 5 percent of the rated capacity of the trap flows through the valve orifice. The pressure on the discharge side of the trap should not be over 25 percent of that on the inlet side if the trap is to function properly.
Figure 22. Impulse trap.
e. Throttling Trap. A throttling trap (fig. 23) operates on the principle that flow of water through an orifice decreases as its temperature approaches that of the steam used. This trap has no moving parts and the rate of flow through it can be adjusted by
raising or lowering the stem which fits a tapered V-seat. With the stem properly adjusted, the condensate, which is slightly cooler than the steam, enters the chamber from the line, travels up through the baffle passage, and is discharged through the orifices. If this discharge is at a rate higher than that at which it enters the trap, the level in the inlet chamber falls until it permits a little steam to enter the baffle passage. The steam going through this passage heats the condensate to a temperature approaching that of the steam. As the temperature increases, the amount of water flashing into steam, and hence the volume of the steam water mixture handled by the orifice increase, and reduce the capacity of the orifice. The reduced flow through the orifice permits the level of condensate in the inlet chamber to rise until the hotter water in the baffle passage has been completely discharged and replaced with water that is slightly cooled. The cycle is then repeated. The orifice vents air from the trap; otherwise, steam would be excluded and as a result, the condensate would cool. This condition results in a high flow through the orifice, dropping the water level and permitting the air to enter the baffle passage and to escape.
20. Strainers
Pipe-line strainers (fig. 24) are used in water and steam lines to prevent foreign matter from entering and clogging equipment. A strainer is used ahead of a trap or a pressure-reducing valve to prevent fouling of the orifice or operating mechanism. Ordinarily, the screen of the strainer is thin sheet metal, usually bronze, monel, or stainless steel. The strainer can be removed for cleaning or it may be arranged with a valve to permit blowing out the foreign material. 1 he strainer must be blown out regularly or examined and cleaned to prevent the flow from being reduced or stopped. If the flow is obstructed, the screen may break and permit foreign material to pass through.
21. Unit Heaters
a. General. A unit heater consisting of an enclosed fan and heater is used to warm and circulate the air. The fan, which is motor-driven, blows air through the heater, which is similar to an automobile radiator. The direction of the air stream is controlled by levers on the front of the heater. Unit heaters are usually suspended from the ceiling or from overhead steam lines. Because of their high capacity, these heaters require large pipes, The simplest
18
— ORIFICE
— DISK
— VALVE
CHAMBER —
CYLINDER —
TU----------------ORIFICE
Q I	ADJUSTING
STEM
RECEIVING
CHAMBER	-----OR)F1CE
H	/
/ RE-EVAPORATING
BALL	K	/	CHAMBER
i W fl
INLET	I	OUTLET
x	HHMi
i I \ __	ifr ’	./
i’-"Fi ■ \ p-*». •	•”* Sr	/ 9
" i ''ter-Jsua^-	Sts	/ S ■■fflnl
JMeI ■
I	F i K	•U^^faa==»>^ T | ■■ lyja	fll
U W I
SPECIAL	f jC mH
gage	7 'mB FhI
glass----11—>	gPSSS-*-!--L	Fl
1^***“*^ ■	’kHB|^b
,^k-	j
f -	/w jMlB^-2. 21	DISCHARGE
\'	----FLOAT TRAP
DRAIN—J	m
C-------I
TO VACUUM '	RETURN
—3 —
Figure 25. Method of handling condensate from high-pressure return to vacuum pump or low-pressure system.
21
purpose a flash tank is installed. If the steam is neither separated nor condensed, water hammer and associated bumping and vibration of lines, severe disturbance of water level in condensate receivers, destruction of float switches, and faulty pump action will result. If traps leak, their leakage adds to this condition.
a.	Flash Tanks. A recommended arrangement of a flash tank and piping connections is shown. (See fig. 25.) Note that the bucket trap discharges below the low-water level. This maintains a water seal to exclude air from the hot piping on the discharge side of the trap. Oxygen corrosion is particularly active in this section if the water seal is not provided. Also, the discharge pipe from the bucket trap helps condense some of the flash steam and thus prevents some loss to the atmosphere through the vent. In a well-designed system, little steam shows at the vent if traps are not leaking. An appreciable plume of steam from a vent pipe is usually evidence of a leaky trap or an open bypass line. In either case prompt attention is necessary.
b.	Condensate Coolers. It is customary to install condensate coolers in return systems, from large installations which utilize steam at high pressure, since a sizeable proportion of the condensate is flashed from high-pressure drips. Examples of such systems are laundries or large high-pressure unit heaters. If flash tanks were used, most of the flash steam would be vented to the atmosphere, since the heat-dissipating capacity of the return system would be insufficient to condense it. The condensate and steam mixture is therefore passed to a heat exchanger which heats the water supplied to hot-water generators. A saving of 10 percent in water-heating costs is easily attained by this method. In addition, the amount of make-up necessary at the boilers is decreased in the same ratio. Flash tanks are provided in high-pressure unit-heater installations, and these tanks are vented through low-pressure unit heaters. The area of uninsulated return lines in the building plus the rating of the low-pressure unit heaters should be 10 to 15 percent of the required equivalent direct radiation (EDR) for 100 psi initial steam pressure. For lower initial pressures the capacity of the low-pressure heaters is decreased proportionately.
23.	Temperature Control Systems
a.	General. Adequate temperature control provides healthful and comfortable temperatures, improves heating efficiency, and results in substantial
fuel saving. There arc three general means of centralized control of heat output of radiators:
(1)	Controlling the rate of steam flow into the radiators by use of inlet orifices and control of the differences in pressure between supply and return lines.
(2)	Controlling the temperature of the steam in the radiators. This is the underlying principle of the vacuum and subatmospheric systems.
(3)	Controlling the length of time that steam flows to the radiators. This is done by admitting steam intermittently and by varying the length of the on and off periods. This method is the most common, and discussion is limited to its various applications.
b.	Room Thermostats. By use of one or two room thermostats, room temperature can be closely and easily controlled. With such a means of control, the temperature of the air next to the controlling thermometer governs the frequency and length of the off-and-on cycle. However, drafts and tampering prevent satisfactory control.
c.	Outside Thermostats. Several systems are used for control of two or more buildings of similar construction. The usual arrangement is to employ an outside thermostat which operates motorized valves to regulate the flow of steam to the building heating system. Advantages of the outside controller are:
(1)	It is more responsive to weather changes, which determine rate of heat loss.
(2)	Tampering is more easily prevented.
(3)	One controller can be used for several buildings.
(4)	Heat is completely cut off when the outside temperature exceeds 65° or some other set temperature.
(5)	Outside controllers are not subject to drafts from open windows.
(6)	Fuel savings of 10 to 20 percent are obtained.
d. Installation. Temperature control systems differ from one manufacturer to another, and elements in one system may be quite different from corresponding elements in some other system. For good results, each system must be installed in accordance with manufacturer’s recommendations.
e. Combination. It may be advantageous to use a system in which the inside or room thermostats are in series with an outside thermostat. The outside thermostat saves fuel by cutting off the heating system when the outside temperature exceeds a set value.
22
24.	Pumps
Pumps which return the condensate are essential parts of all except the smallest and simplest of distribution systems. From the standpoint of heating efficiency, keeping the lines and radiators free from accumulations of condensate is as important as supplying steam to the heating equipment. For this service there are many modifications and special arrangements of pumping equipment. Both steam and electric-driven units are used. A majority of installations use electric-driven condensate and vacuum pumps as units complete with motors and controls. Discussion here is limited to a simple representative example of each type.
a.	Condensate Pumps. (1) Figure 26 shows a typical condensate pump with receiver and float controls. The pump operates intermittently under the action of the float-controlled switch, as shown. The condensate returns by gravity to the receiver from the radiation; it is therefore important that return lines be graded toward the receiver. To prevent pockets of condensate from forming and interfering with the free flow of condensate and noncondensable gases, offset pattern fittings are used where line sizes change.
(2)	Condensate pumps are made in a wide range of sizes. Large units have cylindrical receivers mounted vertically or horizontally. Usually the pump and motor are mounted horizontally. In many cases two pump sets and one receiver are mounted as a unit. Either pump or both can be used as needed. Receivers are vented to the atmosphere.
(3)	In many units the condensate enters near the base of the receiver. If steam traps on the system are leaking or if bypass lines are open, steam coming with the condensate may form large bubbles which cause rapid changes in water level within the receiver. In addition, there is nearly always some flashing of steam in the receiver under these circumstances. The combination may cause such serious fluctuations in water level that the float-switch mechanism may be destroyed in a few hours or a few days at best. Observation of the float mechanism will show what is happening within the receiver. The remedy is obvious: Keep the steam traps in good repair and the bypass valves closed.
b.	Vacuum Pumps. (1) Figure 27 shows the construction and general operating principle of a vacuum return pump. Vacuum pumps maintain a vacuum on the return system and are thus able to drain return lines which would not drain readily by gravity. As explained earlier, the vacuum system
Figure 26. Condensate pump.
also has certain other advantages. The pump shown is arranged so a single impeller serves to pump both condensate and the noncondensable gases (mostly air) which leak into the system or are released in the boiler. Other makes of pumps use similar arrangements ; some use two impellers, one for condensate and one for air. The figure indicates the path of flow through the unit. The returns from the system enter through the strainer into a compartment near the base of the unit. From here it passes to the ejector. Condensate supplied by the pump at high velocity delivers the returns through the venturi tube into the upper receiver. The noncondensables operate here and are vented to the atmosphere. The condensate recirculates through the pump, with a portion of it going to’ the boiler or surge tank as indicated. The float controls the valve which determines the rate of flow to the boiler or tank. A given water level is maintained in the receiver, and the pump may run to maintain vacuum without any appreciable delivery from the condensate outlet.
(2) All such units are fitted with both vacuum and float controls, but neither operating alone can fully accomplish the proper action of a vacuum pump. If any great amount of air leaks into the system, the pump must operate a large part of the time to maintain the set vacuum. The only satisfactory remedy is to eliminate the leakage. Switching over to float control alone allows the unit to operate like a plain condensate return pump and defeats the purpose for which the vacuum pump was installed. Therefore, it is important that the distribution system, the pump, and its controls, be maintained in correct operating condition. Manufacturers’
23
instruction sheets for the particular make of pump	ating and servicing vacuum pumps and their con-
installed are the best source of information on oper-	trols.
AIR-RELEASE CHECK
CONDENSATE TO BOILER OR TANK
-CONDENSATE AND AIR INLET
Figure 27. Vacuum-return pump.
24
CHAPTER 2
HOT-WATER DISTRIBUTION SYSTEMS
25.	General
The distribution system and piping for hot-water heating and domestic supply systems are simpler than those for steam. These systems may be divided into two general classes: the gravity circulation system and the forced circulation system. Temperature of the water handled is from 150° to 250°. The higher temperatures are used with the forced circulation systems. Several items such as supports, insulation, and some valves and fittings are the same for both steam and hot-water distribution. The principal points which pertain exclusively to hot-water systems are discussed in this section.
26.	Elements of Hot-Water Heating Systems A hot-water system has four principal elements:
a.	The boiler or heat exchanger in which the water is heated. The boiler is the same type as that used for low-pressure steam generation. In other cases a heat exchanger of conventional pattern is used and is supplied by steam from a central plant.
b.	The radiators, convectors, pipe coils, or other space-heating equipment. This equipment is identical with that used for steam. Because of the lower temperature of the heating medium, the output of this space-heating equipment is considered to be 75 percent of that for the same square footage in steam radiation.
c.	The piping system through which the hot water flows.
d.	The control system by which water temperature is regulated for various requirements.
27.	Systems of Piping
a.	Gravity Circulation. In practice gravity circulation is limited to a single building. The circulation is set up because of the difference between density of hot and cold water. Velocity of flow through the piping is low, and the pipe size must be large to supply the necessary heat. Pressure heads available for producing circulation are limited. Good results, however, are obtained in well-designed systems.
b.	Forced Circulation. Pressure heads available in forced-circulation systems are much greater than those in gravity systems. Therefore, higher velocities and smaller pipe sizes are usual. Initial cost of the installation is lower. A much shorter heating-up period and increased flexibility of control are also important advantages. Whenever the system is in use, it is necessary to operate a pump, which requires power. Over the life of the system, this cost more than offsets initial savings. For extensive heating systems, forced circulation must be used.
c.	One- and Two-Pipe Systems. One- and two-pipe systems are used with either forced- or gravitycirculation systems. In a one-pipe system water circulates through each radiator in its particular branch and then goes back to the boiler. Radiator temperatures are progressively lower in the direction of flow. With rapid circulation, this variation would not be serious. In a two-pipe system there are separate supply and return pipes throughout, so the radiators are connected in parallel, and the water temperature is the same in each one. The return pipe may be arranged for either direct or reversed return. With reversed return, a return pipe connects all radiators, and the pipe back to the boilers comes from the end of the return pipe which is closest to the last radiator. The length of the water circuit is thus the same through each radiator, and balanced flows result. This arrangement is advisable for large systems. For very large systems the piping is zoned. If unequal branches exist on parts of the system, thermometer wells and control valves on the return pipes are used to balance the flows.
28.	Mechanical Circulators
a.	Centrifugal pumps, usually directly connected, are employed for circulators. They are mounted in the return system near the boiler, since the water temperature is lowest here. The pump is selected on the basis of ability to circulate the required volume of water against the resistance head of the system as designed. Flow velocities above 4 feet per second are likely to cause disturbing noises in
25
the system, so this figure is frequently considered a maximum value for use in design. The required pump capacity is determined from the heating capacity required and the design temperature drop between supply and return piping, usually 20° to 30°. For example, if a capacity of 10,000 Btu is required and a 20° drop is selected, the pump capacity needed would be 5,000 pounds per hour or about 10 gpm. In most large systems the pumps run continually. In small systems operation may be either continuous or intermittent, depending on the type of control equipment used. Many systems employ a valved bypass line around the circulator so that some gravity circulation is possible in case of pump failure. Some large systems use small steam turbines to drive the pumps and use the turbine exhaust to heat the water. If well-designed and adjusted to the heating requirements, this system is economical. However, the steam required to run the turbines may exceed that required to heat water, especially during mild weather. Steam loss to the atmosphere results under these circumstances.
b.	Pipe size has an important effect on pump power requirements. Friction heads increase almost as the square of flow velocities. A larger pipe means lower velocities and reduced power needed to run the pump, but the larger pipe costs more initially. The usual centrifugal circulator has an efficiency of about 60 percent. The cost of power for a large installation must be determined in advance and the annual cost for power compared with cost of piping of various sizes to insure the most economical combination.
29.	Expansion Tanks
When heated, water expands, and the resulting increase in volume must be provided for. Closed or open expansion tanks are used. If a system is filled with water at the usual inlet temperatures and then is heated to 200° the increase in volume will be about 4 percent. This figure may be used as a guide; it is not precise.
a.	Open Expansion Tanks. The minimum volume of an open expansion tank must not be less than 6 percent of the volume of all piping, radiators, and the boiler. An open expansion tank has a free vent to the atmosphere. The tank is located about 3 feet above the highest radiator. For gravity circulation, the pipe to the tank is connected to the supply riser. Air liberated in the boiler passes directly to the tank and out the open vent. For forced-circulation systems, the connection to the tank is made on the suction side of the circulation pump. This
arrangement keeps the head on the pump at a fairly constant value.
b.	Closed Expansion Tanks. A closed expansion tank does not have a free vent to the atmosphere. Air in the system is vented through automatic relief valves. This type usually is located just above the boiler. Expansion takes place in the tank and excess air which is there is vented through the relief valve. It is the usual practice to provide a larger tank than with open expansion. The following rule is frequently used: for a one-story building, make the tank volume 10 percent of piping, boiler, and radiator volume, with an increase in volume of 3 percent for each additional story or equivalent height. If the tank is above the highest radiator a volume of 10 percent is sufficient. Any closed expansion tank should be connected by a direct pipe to the flow main leaving the boiler so any air liberated in heating may pass directly to the expansion tank. No valves should be located between the boiler and the expansion tank. Each tank should have a gage glass, relief valve, and air inlet valve. With large systems, compressed air for renewing the air cushion is desirable. This saves the inconvenience of draining down the system to introduce air at atmospheric pressure.
30.	Installation
Technical details of design of hot-water systems are beyond the scope of this manual; however, the following simple rules are given to help in locating and correcting potential operating difficulties.
a.	Air pockets in piping prevent or interfere with circulation. Therefore, pitch all piping so that air is easily vented through the open expansion tank, radiators, or relief valves, or to the closed expansion tank. Pitch the mains and branches up and away from the boiler or heater at a slope of 1 inch in 10 feet or more.
b.	Make connections from boiler to mains short and direct.
c.	If any circuit is changed or added to, exercise care to insure balanced flows. Installation of thermometer wells and lock-shield flow-control valves will assist in restoring balance.
d.	Provide for drainage of the entire system, preferably in sections.
e.	Make provision for free expansion of 1 inch in every 100 feet of piping.
f.	Unless it is used as heating surface, insulate all flow and return piping.
26
31.	Control
The most important advantage of hot-water heating systems is the flexibility possible by control of water temperature. With this flexibility, heat output of the radiation can be adjusted closely enough to the requirements to prevent wide temperature fluctuations, which are common with other systems during mild weather. Thermostatic devices give on-and-off or, in some cases, modulating control of the burning
equipment or of dampers and motors. Circulating pumps may run continuously, as is the case in many large systems, or they may be controlled by room or outside thermostats. With continuously operating pumps, the water is circulated through the temperature-controlled bypass valves. In any case, control over water temperature must be effective if the extra expenditure for this type of system is to be justified.
27
CHAPTER 3
GAS DISTRIBUTION SYSTEMS
Section I. DESCRIPTION OF SYSTEMS
32.	General
A gas distributing system delivers gas from a source of supply, usually a transmission main, to the services connected to it. The piping network composing a system of this kind can be grouped into three categories : feeder mains, distributor mains, and gas service lines. Feeder mains deliver gas from a source of supply, such as a transmission line, to a district regulator. Gas services are lateral lines extending from the distributor main to the building or point of consumption.
33.	Types of Systems
Distribution systems are of two principal types:
a.	Low-Pressure. In low-pressure systems, gas is normally distributed at pressures of 3 to 8 ounces. In a properly designed system of this type, service regulators are not required at each building served.
b.	Intermediate-Pressure. In intermediate-pressure systems gas is normally distributed at pressures of 2 to 50 psi. In this type of system a service regulator must be installed at each building served, to reduce the distribution gas pressure to about 4 ounces before it enters the building.
34.	Design
In an intermediate-pressure system smaller pipe sizes can be used than in a low-pressure system. If small pipe were used in a low-pressure system, friction and turbulence losses would be so great that the consumer would receive little heat. In intermediate-pressure systems gas flows because of the pressure of 2 to 50 psi, which overcomes friction and turbulence losses. Because of the savings in critical materials, virtually all distribution systems at Army installations which have been built in recent years are of the intermediate-pressure type. Systems intended to last longer than 5 years are designed to use pressures below 20 psi in order to avoid excessive leakage. However, this economic factor has been necessarily ignored in the design of most Army
28
systems because of the temporary nature of the posts and the desire to use minimum quantities of critical materials. Low-pressure systems use pipes ranging from 4 to 12 inches, with 8-inch pipe preferred. In- <. termediate systems utilize pipe 2 to 4 inches in diameter. Standards and requirements of the American Gas Association and the National Board of Fire Underwriters should be observed in the design and installation of gas distribution systems.
35.	Delivery Points
On most small Army posts the gas company’s meter and regulator station reduces the main line pressure to the pressure required on the entire distribution system. On larger posts, it is not feasible to supply the entire distribution system from a single delivery point. In such cases an intermediate- or high-pressure feeder line takes off from the gas company’s station and runs to one or more strategically located district regulator stations, which reduce the pressure to that desired for operation of the distribution system. Stations using district regulators (fig. 28) provide several delivery points into the system, making more uniform and lower average pressures possible. Wherever it is economically feasible large loads such as hospital and laundry boiler plants are served directly from such feeder lines to relieve the gas distribution system of these heavy demands.
36.	Pressures
The amount of pressure necessary for adequate operation depends greatly on the system design. In a well-looped system, the distribution mains are tied in to make an integrated unit. More uniform and lower operating pressures are allowable in such a X system than in a radial type system, in which excessive pressure drops are experienced because of long dead-end lines. In operation of low-pressure systems, the system must be well looped and must use pipe of adequate size. Wherever it is economi> cally feasible, long dead-end lines should be eliminated from both low-pressure and intermediate pressure systems by additional tie-ins.
LEGEND
^£—^3	r---] OUTLET PRESSURE
INLET-PRESSURE- /O/ \4Fl	*--- GAS
ADJUSTMENT FERRULE--7MI4	1 LOADING PRESSURE
z^y	____ gas
W, :	;	IBU	INLET	PRESSURE GAS
/ ) ; /	'	QZLZ2UD z
/ Z QZZZZZZ® '
I / zai j
REMOVABLE FILTER	^^^//////A
FOR PILOT LINE-------x	f\T^
zgl hg 1 frijf |	Sr^W- A-
liWw—
it ^^^77777\
■O £jh-
JNLET - 3|| l|i|'| I P r 1	-OUTLET
-- REMOVABLE
VALVE AND SEAT
Figure 28. District regulator.
37. Pressure Control
Limiting factors in pressure control are usually heavy loads served by a small line, improper regulator sizing, or poorly designed systems with a number of dead ends. Location of the low-pressure point
is necessary as a preliminary step in effecting proper pressure control. If location of the lowest pressure point on the system is unknown it can be approximated by examination of the system map. A dead end at a distant point on the system, or a point
29
where loads are very heavy for the size of supply lines, are likely locations. The exact location can be definitely determined by simultaneously checking several likely locations with indicating-pressure gages (fig. 29) of appropriate range. A recording-pressure gage (fig. 30) installed at this point and furnishing a continuous record of pressure under operating conditions provides the basis for proper pressure control. Pressure maintained must be large enough to give service at all points under operating conditions. In some cases pressure may be lowered through replacement of undersized service regulators, or by increasing the orifice size in the installed service regulator. When orifice sizes are increased, the manufacturer’s specifications for sizes of orifices and inlet pressures should be followed. In some cases line capacities may be increased by replacing short lines serving large loads. The amount of leakage in the systems is the determining factor in deciding whether lines should be replaced. Decrease in operating pressure in a radial type system may not be possible without looping the system. Amount of leakage and expected period of service of the system governs whether or not the looping is to be done.
Figure 29. Indicating.pressure gage,
Section II. CONSTRUCTION DETAILS AND EQUIPMENT
38, Piping
a. Steel Pipe. Steel pipe is widely used in gas distribution systems.
(1) Types of joints. Three types of joints are used: screw coupled (fig. 31), dresser coupled (fig. 32), and welded. Because of excessive leakage, screw joints are the least desirable for 2-inch and larger distribution mains. Less leakage and fewer repairs result with properly welded joints than with any other type. Dresser couplings are often used in a welded line at certain intervals designated by practice and where excessive stresses might develop because of expansion and contraction of pipe or shifting of soil. Dresser couplings are also used in pipe replacement work where a welding torch would constitute a fire hazard.
(2) Corrosion. Steel pipe is subject to corrosion in the ground. The rate of corrosion varies greatly with different types of soil and with the amount of moisture present. Presence of electrical, ammonia, heating, and sewerage lines contributes to corrosion of gas pipes. According to the electrochemical theory of pipe corrosion, now widely accepted, the combination of metal, moisture, and “hot” soil constituents sets up natural batteries. At the point where these currents leave the pipe, pitting of the pipe may become serious in a short time. In other locations where the soil is neutral and dry, bare steel pipe may last for many years. To be effective, a protective coating for pipe must have high electrical and moisture resistance. Thin paints and cold applications are of questionable economic value. Thickness is the controlling factor in effectiveness of the coating material. The recommended thickness of the commonly used coal-tar enamel is %2 inch. Protective coatings properly applied are expensive. It is just as much a waste of money to put an effective coating on pipe in neutral soil conditions as it is to leave pipe unprotected in “hot” areas. Where it is necessary to replace pipe because of excessive corrosion, steel pipe should be coated with a hot application of coal-tar enamel; one man pours the heated material along the top of the pipe while a man on each side of the pipe distributes the coating uniformly around the entire surface of the pipe by use of a sling. Pipe can be purchased mill-coated and wrapped. This may prove desirable where extensive replacement work is required. When mill-coated pipe is used, joints are coated as indicated
30
HINGE--TIME INDICATOR	y----CARRYING
X	/	HANDLE
------MEASURING
V	Z	J4
TRUDNOORY------|	\| I	|---------CASE
Iff KBs ly_; fir 1 INK F(|	'	AT	w—™
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SUPPLY OF	II
CHARTS------^J| XZ'	X.	'"-Si
FX' \	X	/	t - W< X	JT	MICROMETER
- j£/7T^X^kV * \	I	II	ADJUSTMENT
COMBINATION	A-V///Y A	X\\\ \	'! - ^7///>.''/	------INVERTED
ANDLOCK-----*41 WE/ // AZ/ST/	\	><-////	■ '"	Ml	PEN ARM V/IT
■III/	• -\\ c If V/7///WL4 ''WWC'W replaceable
17	i ■> I \ 5	1	T,p
V Lj • -I i f I	I	,n	y •< -~-<—I I It! |1F	S 51 ' I T t j I. j	Y ; j । ~~ j111 "’* T» t, a X i g K|3|K
Beti *	J j I !2i c-’"’t Ki. 1 r I	?' II t,	4 4 |~~4 ■• i \L । lj '.:’! ■	:4^4~4-4-d "I j i L | pOt
^1^^ *1 l i I I 1 V~1 *	—‘•••“i--4	-x,.	’ )' /	. l I / I । i ; I ;; it	Jr ■	" r| <	<	^’***>L. ’'	■ '~Ur**L_i - ■ fl	• Wit
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■lA nVuWrv	'VzCi /7/W7 Jr ■ >1 ALHWavkv^-	-------chart
CHART	m. iVAYV-W bw :--A;j W/H' /! | m\ •-\\Vk'\ v'\V
HOLDER--------BlW B- -' v/ LM \	/ip-— quick-set
\ '	\vx>	k/zA	• /	■	*	IE-	V'AkAxZkr11	chart	hub
L	\	'■ \x:'m	LSAzTZ” /W'5"". - / i .'/'' /	i’w o	Ir	X •■\NW>4ZZt ?^-v’ REINFORCING
.....LJ y	POCKET
L. -------------------—<31 -Jp	FOLLOWER
I I"	t
 r 1 * BUSHING
SOLID DISK-----
I lai o
SEAT RINGS
Figure 42. Gate valve.
39
widely at locations where a continuous pressure record is not required. The chart record from a recording gage is evidence of the performance of regulating equipment. Deviations from the required pressure are noted and corrective measures are taken.
a.	Use. (1) Indicating-pressure gages. As a guide for setting outlet pressures on the regulator and for use as a pressure guide when the regulator is being bypassed, indicating-pressure gages are installed on either side of a district regulator serving a large boiler plant. In addition to the regular recording or indicating high-pressure gages required for normal operation of a high- or intermediate-pressure system, a low-pressure indicating test gage or water column of suitable range is necessary for setting outlet pressures of service regulators.
(2)	Recording-pressure gages. A recording-pressure gage is installed at the low-pressure point of the system. If the system is of large extent with two or more low-pressure points at widely separated location, a recording pressure gage is installed at each of these points.
b.	Inspections. (1) Indicating-pressure gages. Indicating-pressure gages are checked by use of a reliable test gage every 3 months. Gages subject to severe vibrations and shock are tested monthly. If found in error, a gage must have its indicating arm reset.
(2)	Recording-pressure gages. Recording-pressure gages are tested annually with a reliable test gage at the operating pressure. If the recording gage reading is in error, the micrometer adjustment on the pen arm must be regulated. The pen must be clean so it will mark the record on the chart clearly.
Section III. GAS MEASUREMENT
42.	General
Gas is measured either by orifice flow meters (fig. 43) or by positive-displacement meters (fig. 44). Of the two, orifice flow meters cost less and are better suited to accurate measurement of large flows. The positive-displacement meter is more susceptible to wear and mechanical failures. Accuracy of orificemeter measurement is affected by turbulence in the immediate vicinity of an orifice, particularly on the upstream side. Flow-disturbing factors such as regulators, valves, and fittings must be spaced certain minimum distances from the orifice plate, in accordance with Gas Measurement Committee Report No. 2, available through the American Gas Association, New York, N. Y. Positive-displacement
meters give accurate measurement when properly maintained. This type of meter must never be operated above its rated capacity.
43.	Orifice Meters
Orifice meters measure flow by registering the differential pressure drop across a thin-edge orifice plate and recording this drop accurately on a chart. Gage-line (static) pressure at the meter is usually recorded on the same chart. If there is a large change of load, accuracy of measurement is improved by changing orifice plates. Differential readings should be at least 5 inches of water and must not exceed the range of the instrument. The principal differential ranges for orifice meters are 0 to 50 inches and 0 to 100 inches of water pressure. An orifice meter with 0 to 10 or 0 to 20 inches of water-pressure range is sometimes combined with one of greater range for more accurate readings of differential registrations at low rates of flow. This combination is referred to as a zvidc-range installation. Both meters are attached to the same taps in the line, and record the flow until the differential exceeds 10 inches. The readings on the 10-inch meter are used in the calculations as they are more easily determined. When the demand exceeds the differential of 10 inches, the records of the 100-inch meter are used. During the higher rates of flow the 10-inch meter is not recording since the meter is assembled with a long mer-cury-seal connection between the two chambers of the two meters. Check valves on this type of installation are not required to operate until the differential exceeds 120 inches.
44.	Orifice Meter Inspections
Instructions given here apply only to meters which are part of the post distribution system. Meters installed by the utility company for billing purposes are cared for by the company.
a.	Thirty-Day Inspection. Orifice meters which are part of the post distribution system are inspected every 30 days. The inspection consists of—
(1)	Checking the meter for levelness.
(2)	Checking the differential for zero position under operating pressure by operation of valves in meter piping. Close atmospheric valve, open the two equalizing valves, and slowly close valve in line from downstream pressure tap. Reset pen on zero position, if necessary, by use of micrometer adjusting screw on pen arm.
(3)	Checking travel of differential pen along time arc of chart by closing bypass valve from high-pres-
40
PRESSURE TIGHT
DIFFEREN
INTEGRAL
HIGH-PRESSURE
STUFFING BOX
SHIPPING
ADJUSTING
TONGUE-AND-GROOVE
LUBRICANT SCREW STOP
SCALE
GASKET SEAT
DIFFERENTIAL MECHANISM
POSITIVE-SEATING SELF-ALIGNING OVERRANGE CHECK VALVE
MERCURY CHAMBER
NEEDLE POINT
EQUIANGULAR DIFFERENTIAL LINKAGE
DIFFERENTIAL HOUSING AND MERCURY
CHAMBERS —
CHAMBER COUPLING PERMITTING INTERCHANGEABLE DIFFERENTIAL RANGES
MERCURY CHAMBER
DRAIN SCREW
EQUIFLOW DAMPENING VALVE
Figure 43. Orifice flow meter.
41
BALL TYPE IMMERSED UNDERRANGE r CHECK VALVE
Figure 44. Positive-displacement meter.
sure side of meter and bleed gas pressure from low-pressure side of meter. Bleed gas very slowly so the meter will not be overranged. When differential pen nears the limit of range on the chart, slowlv open bypass valve from the high-pressure side of meter so the pen will reverse direction of travel and return to zero position. If pen travel does not follow time arc, adjustment can be made by bending pen point slightly up or down as required. If pen does not travel to full limit of range on chart, add or withdraw mercury (according to make of meter) to give required amount of travel.
(4)	Making sure the clearance between pen points at zero position does not exceed 1/16 to %2 inch. If pen points are adjusted to provide this clearance, recheck time arc ((3) above).
(5)	Testing static pen reading at operating pressure on chart with reliable test gage and resetting to proper pressure, if necessary, by use of micrometer adjusting screw.
(6)	Checking clock movements for proper timekeeping and making adjustment if necessary.
(7)	Checking orifice-plate size stamped on tab or
handle of orifice plate against size of orifice shown on chart.
b.	Ninety-Day Inspection. At 90-day intervals the following items should be added to above inspection :
(1)	Calibrate differential against water column of 50-inch range by the following steps:
(a) Check meter for zero under operating pressure. Check meter piping for leaks by soap testing.
(&) Release pressure from meter.
(c) Reset differential pen to zero, if necessary.
(J)	Attach water column to high-pressure mercury chamber piping, leaving low-pressure chamber open to atmosphere.
0) Close bypass valve leading to low-pressure chamber, leaving bypass valve to high-pressure chamber and bypass bleeder valve in open position.
CD Open main lead valve from high-pressure tap very slowly until 1 inch of water pressure is registered on water column with gas escaping to atmosphere through open bypass valve.
(i?) Calibrate meter by gradually closing bypass valve to give desired reading on water column and chart on upward swing of pen arm, then gradually opening bypass valve to bring water column down to desired reading. Meter should always be calibrated for up and down direction of pen travel.
(2)	If water column and differential chart readings do not agree within 2 percent at any reading on chart, clean the mercury chambers and pressure-tight bearings in accordance with instructions of manufacturer of instrument. If mercury contains dirt or solubles, clean it by washing in a 10 percent’ solution of nitric acid. Remove acid by washing thoroughly in water. Dry mercury by agitating with air under pressure. If mercury is mixed with loose dirt or other insoluble material only, clean it by straining through a clean chamois skin or a clean, lint-free, closely woven cloth. Clean the bearing and repack with grease as directed by manufacturer. After meter is reassembled, check calibration to determine accuracy; if calibration is not satisfactorv, recalibrate instrument by increasing or decreasing length of float lever arm in accordance with manufacturer’s instructions.
(3)	Inspect orifice plate for cleanliness and condition of orifice edge. A plate on which dirt, rust, or scale is built up near the edge of the orifice will give erroneous readings. Wash plate in gasoline, if necessary, and wipe clean with a soft rag. Never let any metal touch sharp edge of plate. Edge should be sharp enough to nick the fingernail if the fingernail
42
is drawn across it. Do not leave bur or other unevenness on or near the edge of the orifice. If the plate is warped, replace it with a new one. Take care when replacing plate to center it in the line; if the plate is beveled on one side place the bevel on the downstream side.
45.	Displacement Meter Inspections
Large positive-displacement meters are tested at 6-month intervals by use of a critical flow or low-pressure flow prover at various rates of flow. Adjustments are made to bring the meter into calibration. Since equipment for making volumetric capacity tests is not ordinarily available at posts, arrangements must be made with the gas company to conduct the tests or to lend the necessary testing equipment. Pressure-pen readings on volume-pressure gages mounted on positive-displacement meters are tested for accuracy by use of a reliable test gage and are reset to proper pressure readings if necessary. Cycle pen ratio is adjusted in accordance with the rate of flow through the meter. Auxiliary measuring devices mounted on positive-displacement meters are tested monthly. The test consists of a check by a reliable test gage or dead-weight test gage of the pressure indicated by the pressure pen of the instrument. If the pen is in error by more than 2 percent, the instrument must be recalibrated. Inspections and recalibrations are made in accordance with instructions given in manufacturer’s manuals on these instruments. Working parts must be lubricated at 6-month intervals as recommended by the manufacturer.
46.	Calculations
Accurate calculations of gas volumes are important, since they indicate operating efficiency of boiler plants and serve as a basis for billing concessions on a post. Knowledge of methods are also essential in checking gas volumes as represented by gas company meter charts. All gas metered to a post through meters of any type must be checked by the post engineer before bills are certified for payment. Daily inspection of these charts by the engineer will help reveal any irregularities such as increased delivery or decreased main-line pressures and will serve as a check on fuel conservation. In some cases, compensating totalizing devices are used on positive-displacement meters, giving a corrected direct reading on the amount of gas passed through the meter. The usual dial reading gives the uncorrected amount of gas passed through the meter. Some meters indicate both the corrected and uncorrected gas flow on sepa
rate dials. If pressure on the meter is constant or nearly so, the corrected dial reading can be checked approximately by applying a pressure multiplier to the reading of the uncorrected dial. Complete information on gas volume measurements by positivedisplacement meters and orifice meters is given in appendixes I and II. These instructions used with witnessed meter tests and witnessed orifice plate changes in the gas company meter station will enable the post engineer to check on the measurement of gas supplied to the post. Knowledge of chart calculations is also essential in running leakage tests on the distribution system.
Section IV. Maintenance
47.	Gas Distribution System Map
A complete gas distribution system map must be available to all post personnel engaged in operation and maintenance of the gas system and to the fire chief. This map is drawn to an appropriate scale, must show the size and kind of all mains and services and their location with respect to streets, and must show all other major structures related to or served by the gas system. Valve and district regulator installations are designated by assigned number. Posts of considerable area should have a general layout map in addition to maps drawn on separate area sheets to convenient scales. Any changes or additions in piping or other installations are entered in this record, and all other copies must be kept up to date. Successful operation of a system depends to a great extent on the accuracy of the map.
48.	Emergency Gas-Curtailment Procedure Posts must be prepared for emergencies arising from gas shortages caused by line breaks or deficient supply. In preparation for such emergencies, it is necessary to plan for the curtailment of all but the most essential services, such as cooking, minimum hot-water requirements, and hospital needs where standby fuel has not been provided. The connected load, as determined by an accurate equipment survey, is used as a basis for developing this plan. The following suggestions are offered as a guide:
a.	Identify and list buildings with corresponding connected load in the order in which they will be cut off.
b.	Assign personnel responsible for carrying out this plan. Accurate distribution-system maps and standard operating procedure for the curtailment program must be available to all personnel thus assigned.
43
c.	Conduct drills and check time required to place program in effect after notice is given. Drills should include placing boiler plants on oil for a 2 hour period if the plants are equipped for oil stand-by.
d.	Impress personnel responsible for carrying out this program with the need for performing required curtailment as quickly as possible.
49.	Emergency Cut-Off
Each post should have material and equipment on hand for proper handling of emergencies which may arise in the gas distribution system. Breaks in mains or other piping sometimes occur accidentally. Because of the serious loss of gas with the resulting danger of asphyxiation or explosion, repairs must be made promptly and efficiently. If the system is section-alized and valves are installed, gas can be quickly cut off. There may be times when it is impossible to isolate a break and cut off the gas supply by means of valves. In such cases the gas flow can be blocked off by means of bags and stoppers by the method commonly used in connecting service lines to an existing main. (See fig. 45.) This procedure applies to low- and intermediate-pressure lines only; valves must be used for high pressure.
a.	Gas-Main Bag. A gas-main bag is canvas covered or made of rubber and is connected to a piece of tubing so it can be inflated. When used to bag off a main, the bag is inserted through a hole cut in the top of the main, then inflated. The inflated bag fills the pipe and thus stops the gas flow. Plain rubber bags serve the purpose except in pipes coated with tar or oil, in which case canvas bags are necessary. Canvas-covered cylindrical bags are used for
intermediate pressures. These bags are pulled into place and held by small cables on each end. Two holes are necessary, the one on the upstream side being closed by a special cable-holding fitting. This form of bag is inflated by a tire pump. It is also fitted with a pressure gage on the inflating line and will hold against a gas pressure 60 percent of that registered by the gage.
b.	Gas Stopper. A gas stopper is a flexible steel frame with an oiled or a rubber-coated canvas stretched over it. In use it forms an impervious partition inside the pipe. The construction of the edge insures a reasonably good seal. To use the stopper, a hole is made in the main, and the stopper frame squeezed together and inserted through the hole. The stopper is brought back to its circular shape by means of attached wire levers. Two stoppers inserted through the same hole are sometimes used. In larger mains it is safer to use both bag and stopper.
50.	Leakage Control
Leakage control is important in maintaining a gas distribution system. Leakage of gas is wasteful and constitutes a serious hazard. Because natural gas has no odor, large amounts may leak undetected for a long period. However, it is standard practice by most companies to add a malodorant to the gas. In other underground utilities, leakage is more readily detected and repairs are more readily made.
a. Locating Leakage. (1) Valves. Maintenance of valves is essential to leakage control. In many cases, periodic lubrication of plug valves lowers the leakage cost enough to eliminate the need for further expenditure of money and labor in leakage location.
-V—* -------RISER PIPE	RISER PIPE----»■
^^SIDE ELEVATION	j I	j	SIDEELE^TON^^^*"
GAS-MAIN BAG	GAS STOPPERS—L
Figure 45. Gas-main bag and gas stoppers.
44
Valves arc kept well lubricated to eliminate one source of avoidable leakage and thus to give more significance to the results of leakage tests. Lubrication extensions (par. 40u) are useful in keeping valves lubricated at a reasonable cost.
(2)	Gas odorization. Odorization of gas is the best known aid in detecting and locating leaks and preventing asphyxiation. A smelly substance called a malodorant is added in a fixed ratio to all gas delivered to the distribution system, unless the gas has sufficient natural odor to act as a warning agent when unburnt. An increase of malodorant to the system in calm, damp weather results in an increase of leaks being reported. The proportion in which the malodorant is added is usually governed by an orifice or a valve partly closed. The ratio of the amount of malodorant injected into the system during any given period is checked by dividing the amount of malodorant used by the amount of gas purchased. The following proportions of malodorant are recommended by manufacturers:
Pentalarm:	pound per million cubic feet.
Calodorant: 2 gallons per million cubic feet.
Ethyl mercaptan : 1 pound per million cubic feet. Amounts may vary somewhat from the above recommendations.
(3)	Line walking. Line walking is the most economical method of locating leaks and is performed as part of the regular preventive maintenance schedule. This procedure is most effective when performed in calm, damp weather, preferably late in the afternoon or early in the morning. The quantity of malodorant in the gas is increased several hours before line walking is performed. Line walkers must be alert for any signs of leakage such as gas odors, dead vegetation, bare spots in grassy places, unusually dry spots of ground, bubbles in water puddles,
and abnormal swarms of flies. Since gas may travel for some distance underground, attention must be paid to surrounding areas as well as to ground immediately over the line.
(4)	Bar testing, (a) Procedure. Bar testing of lines is the most accurate and most expensive method of locating leaks. It is used extensively only in sections of the distribution system which have leakage in excess of $75.00 per mile of pipe per year. Bar testing consists of driving a bar in the ground beside the pipe to the depth of the pipe and then flash testing the bar hole for indication of leakage. In certain kinds of soil the leaking gas or the heat of the sun tend to form a crust over a leak, thus forcing the leaking gas along the pipe or in different directions through the soil instead of directly to the surface. If the bar is driven into the ground in several places and gas burns at a number of bar-hole openings, the direction of the leak is found by comparing the sizes of the flames at the openings. As the distance between the bar holes and the main leak is decreased, flames increase in size indicating the point at which to make repairs. Use of the bar illustrated in figure 46 reduces the expense of bar testing.
(b) Crew. The normal bar-testing crew consists of one supervisor and at least three laborers. A crew of this size is more effective than a smaller crew, since the workers can stay immediately over the line by visually lining up on the other workers. Lining up can be made easier by setting markers immediately above the line at intervals of approximately 100 ft. The distance covered per day by a bar-testing crew of given size will vary directly with the spacing interval between bar holes. The usual interval between bar holes is from 3 to 20 feet, depending on local soil and pipe-line conditions.
(c) Classifying leaks. Leaks are classified as fol
3" RD STEEL WITH I*---------- I'-O"------*
%" DRILL ON
l!4"k-3%'4.	-> <- 3/4”	---3/4" TOOL STEEL - HEX OR ROUND
—
=i Hfilill x flliw
■ v -■ tZ~ZZ	A	R
V 9\/^Wf§/	3
J ^V7 >Orz	I
METER INDEX-START OF PER 10D^<^_/dA V OjJ^'METER INDEX - END OF PERIOD	|
a°^°o
n9^K/« • A(£< v§VK	S’
f k ^Ta/xTTJt8 • 9	/2>'	X16/	XlZ	P
CUBIC	'
___2^^_^____]	FEET	|
READING: I,053,000 CUBIC FEET	READING: I,301,900 CUBIC FEET	I
Average Gage Pressure = —— = 25,6 psi	•*'
Average Absolute Pressure = 25.6 psi + 14.4 psi = 40.0 psi
Pressure Multiplier = -?r-	40P81-r = 2.6846	|
0.5 psi + 14.4 psi
Contract Volume = (1,301,900 cu ft - 1,053,000 cu ft) x 2.6846
= 668,197 cu ft
Figure 47. Positive-displacement gas-meter chart.
50
often the measurement job is assumed to be over when the index is read. Figure 47 shows a typical meter index for the example chart at the beginning and end of the chart period. Note that the first dial at the right is marked 1,000. This means that the hand makes 1 complete revolution each time 1,000 cubic feet of gas pass through the meter. Since the dial is divided into 10 equal parts, each division represents 100 cubic feet. Therefore, add two zeros to the index reading to show the volume indicated in cubic feet. Note also that a complete revolution of each of the other dials represents 10 times as much gas as that of the next lower denomination. When a hand is very near a dial figure, it is often difficult to tell whether that figure or the next lower one is correct. For example, on the right-hand index the 10,000-cubic-foot dial hand is practically on 2. However, from the reading of 9 on the next lower denomination dial 1,000 cubic feet, it can be seen that a complete revolution has not yet been made. Therefore, the proper reading of the 10,000-cubic-foot dial is 1. On the same index the 1,000,000-cubic-foot dial hand has completed a revolution and is slightly past zero on the next revolution. The proper reading of the 1,000,000-cubic-foot hand is therefore 3. The index is read when the chart is placed on the meter and is read again when the chart is removed. These readings and the date and time are written on back of the chart.
g. 4 he hand on the dial marked “ten feet” makes one revolution each time 10 cubic feet of gas pass the meter. 4 his dial is used in testing the meter and in checking very low rates of flow during a distribu
tion system leakage test. However, in the ordinary leading of the meter the “ten feet” dial is ignored.
h. (1) The volume cycle of the chart is determined by observation of the chart and the meter index. If the 1,000-cubic-foot dial hand makes 1 complete revolution each time the chart volume pen records a complete cycle, the chart volume cycle is 1,000 cubic feet. On the other hand, if the 1,000-cubic-foot dial makes a complete revolution each time the chart volume pen records a complete cycle, the chart cycle is 10,000 cubic feet.
(2) The above determination is made because the total chart cycles give a check on the accuracy of the meter readings. For example, by actually counting the 10,000-cubic-foot volume cycles on the attached chart one can see that there are slightly less than 25 such cycles. This checks with the meter index consumption of 248,900 cubic feet.
i. In the operation of a gas distribution system, it is often desirable to know maximum and minimum houi ly rates of flow and the time such rates occur. On a 7-day pressure-volume chart it is difficult to calculate maximum and minimum hours because of the compressed time scale. However, the shortest and longest cycles can be determined and their average hourly rates of flow computed. For example, on the chart below one of the maximum demand periods (shortest cycle) occurred from 7 to 11 AM Tuesday, and the minimum demand period (longest cycle) was from 1 :30 to 11 :30 PM Sunday. Calculation of the average hourly rates of flow for these two periods and for the entire week are as follows:
Period	Hours	Meter volume (eu ft)	Average gage pressure (psi)	Pressure multiplier	Contract volume (cu ft)	Average rate of flow (cu ft per hr)
7-11 AM, Tues		4	10,000	23.6	2,5503	25,503	6,376
1:30-11 :30 PM, Sun		10	10,000	26.2	2,7248	27,248	2,725
W eek		168	248,900	25.6	2,6846	668,197	3,977
6.	Summary of Measurement Computations
a.	Determine following from contract:
(1)	Base pressure in psi absolute.
(2)	Whether actual or an assumed atmospheric pressure is to be used.
(3)	Whether a temperature correction is to be applied.
b.	Read meter index at start and end of chart period and record on back of chart along with date and time of reading. (See par. 5/.)
c.	Determine whether volume cycle of chart is 1,000 cubic feet or 10,000 cubic feet by checking
against the. 1,000-cubic-foot meter index dial. (See par. 5A.)
d.	With a pencil mark off the chart volume cycles on the pressure line. (See par. 5c and (Z.)
e.	Read the average pressure for each cycle and write it on chart in the appropriate cycle period. (See par. 5c.)
f.	Add the pressure readings and divide by the total number of reading to determine the average gage pressure. (See par. 5c.)
g.	Convert the average gage pressure to absolute pressure by adding to it the actual or assumed
.•51
atmospheric pressure, as provided for by the contract. (See par. 4.)
h.	Determine the pressure multiplier by dividing the average absolute gas pressure by the absolute contract base pressure. (See par. 5a.)
i.	Multiply the difference between the beginning and ending meter index readings times the pressure multiplier to determine the correct volume at the contract base pressure. (See par. 5a.)
j.	Correct the volume for temperature i f contract so provides. (See par. 5a.)
7.	Maintenance
The positive-displacement meter is remarkable for its accuracy and reliability over long periods. The accuracy of the meter can be maintained by proper attention to the following:
a.	Gas must be clean and dry to avoid excessive wear of valves and other moving parts.
b.	Avoid sudden changes in pressure, since they arc liable to damage the meter diaphragms. When meter is being put in or taken out of service, open and close valves slowly.
c.	Avoid operating meter at flow rates and working pressures in excess of its designed capacity. See table II for meter capacities.
d.	To prevent excessive wear of the meter mechanism, eliminate pulsating pressures from nearby regulators by repairing or adjusting the regulators.
e.	Ordinarily, testing equipment for volumetric tests is not available on the posts. However, the principal source of error is usually the recording-pressure gage and this can be checked easily by an accurate indicating-pressure gage. Gas companies’ meters should be tested in accordance with provisions of the contract.
52
Tabic II. Positive-displacement gas meters maximum hourly meter capacities
Meter		Cubic foot per hour capacities at various gage gas pressures (expressed at 4-ounce base pressure)							
Make	Mode! No.	4 oz	5 psi	19 psi	15 psi	20 psi	3') psi	50 psi	75 psi
Metric	5 B	175								—	
	10 B	250							
	20 B	350	900	1,000					
	25 B	400	1,100	1,300	1,500	1,700	2,100	2,800	3,500
	30 B	550	1,400	1,600	1,900				
	35 B	650	1,900	2,200	2,600	2,900	3,500	4,600	5,900
	60 B	950	2,500	3,000	3,400	3,800	4,700	6,100	7,900
	80 B	1,200	3,100	3,700	4,300	4,800	5,800	7,700	9,900
	250 B	3,000	7,500	8,900	10,000	12,000	14,000	18,000	24,000
	500 B	4,800	12,500	15,000	17,000	19,000	23,000	31,000	39,000
Emco	0	175							
	1	275							
	2	415							
	2G	850	2,320	2,800	3,230	3,640	4,360	5,500	7,000
Crank Type	3	1,200	3,230	3,880	4,500	5,000	6,100	7,600	9,700
	4	1,700	4,900	5,900	6,800	7,700	9,200	11,900	14,800
Gear Type	4	2,250	6,400	7,800	9,000	10,100	12,100	15,300	19,300
	F/>	3,000	7,700	9,300	10,800	12,100	14,500	18,300	23,300
•	5	5,000	12,900	15,500	18,000	20,200	24,200	30,500	
Pittsburgh	1	165							
	2	265							
	3	365							
	4	960							
Sprague	1 A	175							
	2	305							
	3	400							
	5	856							
Tobey	A	150							
	B	250							
	1	150							
	2	250							
	4	780							
Tin Case	5 B	150							
	5 A	175							
	10 B	300							
	10 A	375							
	20 B	450							
	30 B	600							
	30 A	875							
	60 B	1,300							
Note-. Four-ounce capacities are based on %-inch water-pressure loss across meter, which is considered maximum desirable on a low-pressure distribution system. On an intermediate-pressure distribution system pressure losses of 1 or 2 inches of water are permissible. To determine the approximate meter capacities at 4 ounces, for 1-inch water-pressure loss, multiply capacities shown by 1.4; for 2-inch water-pressure loss miiltinlv hv 9	1	• n,
53
APPENDIX II
GAS-VOLUME COMPUTER FOR ORIFICE-METER CHARTS
1.	General
The computer chart (fig. 48) has been designed to make it possible to calculate gas volumes rapidly and accurately by orifice meters. The maximum error of the computer is approximately 1 percent. The computer is useful for the following purposes:
a.	Checking the gas company’s billing.
b.	Checking maximum hourly rates of flow to determine minimum pressures which can be carried on the gas distribution system.
c.	Checking minimum hourly rates of flow, in leakage tests.
d.	Computing gas volumes of post laundries and hospitals having orifice meters.
2.	Procedure
The computer is designed for use with standard orifice-meter charts having uniform scale divisions. It cannot be used with direct-reading square root charts. The orifice meter is a combination of a Bourdon-tube gage for measuring line pressure and a U-gage for measuring the differential or pres-
sure drop across the orifice in inches of water. The static line pressure is usually recorded by a blue line and the differential by a red line. From these data the volume of gas is computed by applying the following equation :
Q = C — X P
\\ here: Q = cubic feet of gas.
C = the hourly coefficient, which is determined by diameter of pipe line and orifice, type of meter connections, contract pressure and temperature base, and specific gravity of the gas.
II = the differential across the orifice in inches of water.
P = the absolute line pressure.
Note. Absolute pressure is gage or indicated pressure plus atmospheric pressure.
a. The coefficient can be calculated from tables HI, IV, V, and VI. After coefficients for a particular installation have been calculated, the various orifice sizes are marked on scale D of the computer. The following example illustrates the calculation:
54
DIFFER IN( OF V A 100 -90 4 80 - 70 4 60 4 50 H 40 4 30 - 20 Z 15 - 10 - 9 - 8 - 7 - 6 -	ENTIAL	EXTENSA :hes VATER 120 -j no 4 100 4 90 - 80 70 - 60 — 50 4 • 40 - 3° 20 - 15k	ON	VOLUM CUBIC FEET E 120,000 -110,000 -100,000 - 90,000 -80,000 j 70,000 -| 60,000 -| 50,000 -| 40,000 -| 30,000 -4 20,000 4 15,000 4 10,000 - 9,000 3 8,000 i 7,000 4 6,000 1 5,000 4 4,000 -:	E	qi	a	tn		~qoou>o— o	O	O	O	OOOOOOOO^.^ t I 1 1 1 1 I I 1 1 1 I t 1 1 I 1 I 1 1 I 1 1 1 1 1 1 1 1 1 I 11 11111 1111 1 III lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllinil 11111 nj Q — ±	C	HO COEF E D	URLY FICIENT - 1000 4 900 4 800 4 700 F 600 - 500 4 400 - 300 - 250
i ' r— 1 •1 ■111	। ' i. -j ! , ।	;—T—।	— ID	xt	IO	CU	10 4 9 4 8-1 7-. 6- 54 4- GUIDE (1) ALIGN A AND B, READ (2) ALIGN C AND D, REA C	3,000 4 2,000 -2 1,500 - 1,000 - 900 - 800 k 700 k 600 4 500 4 400 OR HOLD C, EXTENSION D E', CUBIC FEET			20 - 15 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 -	3	- 200 E 190 P 180 k 170 k 160 E 150 140 4 130 E 120 4 HO - 100 0
			—								
—		C		E'					—	
NOTES: GAGE STATIC B BASED ON 14.4 PSI ATMOSPHERIC PRESSURE.
IF HOURLY COEFFICIENT IS BEYOND SCALE, MULTIPLY SCALES D AND E BY 10
Figure 48. Gas volume computer for orifice meter charts.
55
Table III. Orifice coefficients for gas
These values are based on the following conditions: base pressure, 14.4 psi + 8 oz. (14.9 psi absolute) ; base and flowing temperature, 60° F; specific gravity, 0.60.
Diameter of orifice	Size of line=3"		Size of line=4"		Size of line=6"		Size of line=8"		Size of line=10"		Size of line=l 2"	
	Type connections		Type connections		Type connections		Type connections		Type connections		Type connections	
finches)	Pipe	Flange	Pipe	Flange	Pipe	Flange	Pi pe	Flange	Pipe	Flange	Pipe	Flange
%	37.26	36.76										
1%	66.96	65.36	66.4	65.36	66.0	65.36						
%	105.50	102.12	104.2	102.1								
%	153.59	147.05	151.1	147.1	149.3	147.1						
z8	211.80	200.15	207.4	200.2								
1	281.20	261.42	273.4	261.4	267.4	261.4	265.3	261.4	264.5	261.4		
iy8	363.28	330.86	349.8	330.9								
	460.08	408.47	437.4	408.5	422.1	408.5	417.0	408.5	414.8	408.5		
	574.27	495.74	536.7	494.3								
P/2	709.27	595.75	648.7	588.2	615.3	588.2	604.6	588.2	599.7	588.2	597.6	588.2
	869.34	710.71	775.8	690.3								
i%	1059.6	843.09	921.0	801.6	849.6	800.6	829.7	800.6	820.3	800.6	816.6	800.6
2	1556.9	1171.9	1271.9	1061.9	1128.0	1045.7	1093.4	1045.7	1077.7	1045.7	1071.0	1045.7
2M			1724.9	1383.9	1458.7	1323.5	1399.6	1323.5	1373.5	1323.5	1362.1	1323.5
P/2			2315.9	1783.9	1847.1	1633.9	1748.2	1633.9	1707.9	1633.9	1690.1	1633.9
2M			3096.6	2281.1	2309.8	1984.7	2144.1	1977.0	2083.5	1977.0	2056.0	1977.0
3					2853.6	2387.6	2593.7	2352.8	2501.4	2352.8	2461.4	2352.8
3K					3502.1	2851.5	3100.6	2761.3	2959.4	2761.3	2907.7	2761.3
3U					4277.1	3386.8	3681.3	3206.1	3478.9	3202.4	3396.9	3202.4
3%					5198.8	4005.3	' 4335.3	3698.9	4046.6	3676.2	3931.5	3676.2
4					6301.2	4719.9	5078.0	4246.0	4669.9	4182.7	4514.6	4182.7
4U							6886.5	5531.5	6124.7	5304.7	5840.4	5293.8
5	Note.	Type pressure tap connections from pipe line					9242.4	7127.2	7898.7	6623.2	7409.5	6536.1
P/2	to orifice meter.						12360.0	9109.9	10070.0	8182.4	9268.5	7946.1
6	Pipe connections: connections are made 2+> pipe-line								12758.0	10031.0	11476.0	9568.4
	diameters upstream and 8			pipe-line	diameters down-							
6)z£	stream of orifice.								16076.0	12228.0	14106.0	11440.0
7	Flange connections: connections are made in flange,										17246.0	13603.0
7H	1 inch upstream and 1 inch downstream of orifice.										21006.0	16107.0
8											25509.0	19004.0
See tables IV, V, and VI for correction multipliers to actual conditions.
Table IV. Multipliers for base pressure
Contract pressure base			Multiplier
As specified		Absolute psi	
11.4	psi + 8 oz	11.9	1.2521
12.1	+ 8 oz	12.6	1.1825
13.0	+ 8 oz	13.5	1.1037
13.2	T8 oz	13.7	1.0876
13.3	+ 8 oz	13.8	1.0797
13.5	H“8 oz	14.0	1.0643
14.4	+4 oz	14.65	1.0171
12.5	+38.4 oz	14.9	1.0000
14.4	+ 8 oz	14.9	1.0000
14.65	+4 oz	14.9	1.0000
14.4	+ 10 oz	15.025	.9917
14.7	+8 oz	15.2	.9803
14.73	+ 8 oz	15.23	.9783
14.4	+2 psi	16.4	.9085
Base pressure multiplier =	—---------------14.9 psi________________
.	New base pressure in pounds absolute
Use to correct coefficient to actual contract pressure base.
7 able I . Multipliers for specific gravity
Specific gravity	Multiplier	Specific gravity	Multiplier	Specific gravity	Multiplier
0.50	1.0954	0.60	1.0000	0.70	0.9258
0.51	1.0847	0.61	0.9918	0.71	0.9193
0.52	1.0742	0.62	0.9837	0.72	0.9129
0.53	1.0640	0.63	0.9759	0.73	0.9066
0.54	1.0541	0.64	0.9682	0.74	0.9005
0.55	1.0445	0.65	0.9608	0.75	0.8944
0.56	1.0351	0.66	0.9535	0.76	0.8885
0.57	1.0260	0.67	0.9463	0.77	0.8827
0.58	1.0171	0.68	0.9393	0.78	0.8771
0.59	1.0084	0.69	0.9325	0.79	0.8715
Specific gravity multiplier = +_________________________0-60_________________
J actual specific gravity
Use to correct coefficient to actual specific gravity.
56
Table Ul. Multipliers for flowing gas temperature
Flowing temperature (de rees F.'i	Multiplier	Flowing temperature (degrees F.)	Multiplier
3 )	1.0302	60	1.0000
31	1.0291	61	0.9990
32	1.0281	62	0.9981
33	1.0270	63	0.9971
34	1.0260	64	0.9962
35	1.0249	65	0.9952
36	1.0239	66	0.9943
37	1.0229	67	0.9933
38	1.0219	68	0.9924
39	1.0208	69	0.9915
40	1.0198	70	0.9905
41	1.0188	71	0.9896
42	1.0178	72	0.9887
43	1.0167	73	0.9877
44	1.0157	74	0.9868
45	1.0147	75	0.9859
46	1.0137	76	0.9850
47	1.0127	77	0.9840
43	1.0117	78	0.9831
49	1.0107	79	0.9822
50	1.0098	80	0.9813
51	1.0088	81	0.9804
52	1.0078	82	0.9795
53	1.0068	83	0.9786
54	1.0058	84	0.9777
55	1.0048	85	0.9768
56	1.0039	86	0.9759
57	1.0029	87	0.9750
58	1.0019	88	0.9741
59	1.0010	L)	0.9732
I lowing temperature multiplier =4/----------------------
J tbO actual Mowing temperature
Note. Many gas contracts provide that the temperature of the gas shall be assumed to be 60°F. In such event, this correction factor is not applied.
Use to correct coefficient to actual flowing gas temperature, if contract so provides.
(1) Given—
Size of line: 4 inches. (Table III.)
Size of orifice: 1% inches. (Table III.)
Type of connections: Flange. See explanatory note at bottom of table III.
Contract pressure base: 14.4 psi plus 4 ounces. (Table IV.)
Actual specific gravity: 0.65, determined by gas company’s periodic tests. (Table V.)
Contract temperature base: 60°F. Contract states that temperature of gas will be assumed to be 60°F. (Table VI).
(2) Then-
Base	Flowing
Pres-	Specific Temper-
Base	sure	Gravity	ature
Coeffi-	Multi-	Multi-	Multicient,	plier,	plier,	plier,
Table	Table	Table	Table
HI	IV	V	VI
Coefficient =--------- ------------ ----------- ------------
330.9 X 1,0171 X 0.9608 X 10,000
= 323.37
b.	I he other part of the orifice meter formula, ■y/ A X /J, is known as the extension. It is scale C on the computer. The coefficient, scale D, times the extension equals the quantity of gas in cubic feet, scale E.
c.	In reading orifice meter charts by the sight method, the average differential and gage line pressures for each hour are determined by sight and written on the chart in the appropriate hourly period. The correct average reading is one which gives an equal area bounded by the actual pen line above and below the average line.
d.	After both differential and gage line hourly readings have been written on the chart, the extensions for each hour can be determined by step 1 of the computer guide and written, for each hour, near the outer rim of the chart.
c. To determine the total quantity of gas passing the meter for the chart period, usually 24 hours, the extensions are totaled and then multiplied by the hourly coefficient (step 2 of computer guide). This calculation gives the quantity of gas passing through the meter during the 24-hour period. If the extension total is beyond scale C, multiply scales C and E by 10. To determine the total gas passing through the meter during any specific hour, multiply the hourly coefficient times the extension for that hour.
f. To determine the hourly rate of flow at any given moment, read the differential and static for that moment and perform steps 1 and 2 of the computer guide. (See fig. 48.) This information is useful in finding maximum and minimum demand for the particular season of the year.
3. Summary of Orifice-Mefer-Chart Calculations
a.	Determine pipe-line size of meter run.
b.	Determine orifice size being used. The diameter of the orifice is shown on the reverse side of the orifice-meter chart. It is also stamped on the handle of the orifice plate.
c.	Determine by observation whether orifice-meter installation has pipe or flange connections.
d.	The above data will make it possible to find the
57
coefficient from table 3. This coefficient must then be corrected to the contract measurement base and actual specific gravity in the example of paragraph 2a.
e.	Read the average hourly differential and static pressures for each hour.
f.	Determine the extensions applicable to the
hourly differential and static readings by performing step 1 of the computer guide.
g.	Determine the quantity of gas in cubic feet by multiplying the coefficient times the sum of the hourly extensions for the desired period. This is accomplished by performing step 2 of the computer guide.
58
APPENDIX III
GAS DISTRIBUTION SYSTEM LEAKAGE TESTS ON INTERMEDIATE-PRESSURE SYSTEMS BY PRESSURE-CHANGE METHOD
1.	Basis
J he test is based on the fact that leakage from intermediate-pressure systems increases with increase in gage distribution pressure.
2.	Test Period
The test period is preferably 4 days, with a minimum period of 2 days. 1 he test should start on Monday or Tuesday to avoid including weekends, when flow characteristics usually vary from normal.
3.	Test Time
The test time is from 1900 to 0600 each night, when a substantial portion of the fluctuation load is off.
4.	Accuracy
I he accuracy of the results depends on obtaining accurate hourly rates at the gas company’s delivery meter. If meters are located on the post at hospitals and laundries or other large consumption points that operate on a 24-hour basis, a somewhat more accurate analysis can be made by including their hourly consumption in the tabulated test data.
5.	Preliminary Steps
Before starting the tbst, check the above measuring installations, then follow the procedure outlined below:
a.	At orifice meter locations, zero the differential to find out whether the differential pen is properly set. Check the charts for preceding days to determine whether the night differential is below 4 or 5 inches of water pressure. If so, an orifice of smaller size must be installed in order to increase the night differential for more accurate readings. In determining proper size of orifice, give consideration to the day load to prevent the differential from exceeding maximum range of chart during the day period.
b.	The supplying gas company can assist in making the above decisions. The company will prefer to make any meter adjustments or changes in orifice sizes on its meters. If the gas company is handling pressure regulation, it will also prefer to handle pressure changes.
c.	Where positive meters are installed with recording pressure-volume gage, it is necessary to read the meter index each hour if the night volume cycle is over 1 hour. The gage line pressure at the meter is determined by the recorded pressure on the meter chart to correct the meter index volume for pressure.
d.	Some positive meters have a base pressure index or Emcorrector which automatically corrects volume to the contract pressure base. A recording pressurevolume gage may or may not be installed in such cases. Practically all indexes of positive meters read in corrected increments of 1,000 cubic feet. Therefore the other index on these meters should be read, since it reads the incorrected volume ordinarily in increments of 100 cubic feet. To correct the readings of this index for line pressure, the line pressure is also read hourly from the pressure indicator on the index. If the pressure fluctuates appreciably at the meter installation, a recording pressure gage should be used to determine the true average hottrlv pressure.
e.	The form shown in figure 49 should be used to mark the positive-meter index readings each hour to avoid possible errors in such readings.
6.	Test Procedure
The test procedure is as follows:
a.	On the first day set the gage distribution pressure at the normal summer operating pressure.
b.	()n the second day double the gage distribution pressure or increase it to the normal winter operating pressure, whichever is the lower.
59
.............................Co	No
(Company Owning Instrument)
Contract with .......................................................
Location ............................................................
Serial No of Instrument..........................Size or Kind............
AM	AM
Chart on ....’.....PM Date ............Chart	off.........PM	Date.......
For Orifice Meter—Orifice No.....................Orifice	Size...........
FOR POSITIVE METER Ft Per Cycle
100 Million 10 Mi 11 ion 1 Mi 11 ion 100,000	10,000	1,000
©©©©©© ©OGOOO ©ooooo gggggg ©g©©o© gggggg ©©©©©©
______________pni
8	PM 	psi
9	PM 	psi
10	PM 	_ps 1
11	PM
______________psi
12	PM 	psi
1	AM
______________psi
2	AM
______________psi
3	AM 	psi
4	AM 	 psi
5	AM 	 P=i
6	AM 	ps I
©G©G©O ©OOGO© ©©©O@O o©©©©© GOGGGO
Figure 49. Form for recording posHive-meler index readings.
60
c.	On the third day, reduce the gage distribution pressure to the normal summer operating pressure.
d.	On the fourth day, again increase the gage distribution pressure to the pressure used on the second day.
c.	If the intermediate-pressure system is supplied by district (pounds to pounds) regulators, the pressure between the supplying meter stations and the district regulators, and the pressure downstream of the district regulators will be increased and decreased in the same ratio during the above test periods.
f. The quantities of gas for each hour of the night test periods are read and tabulated from the recording meter charts or by actually reading, the meter indexes hourly as set forth in paragraph 5 above.
g. At conclusion of the test, reduce the distribution pressure to the minimum required for adequate service.
7. Compiling and Analyzing Data
ct. 1 abulate the resulting data as shown on the leakage test form. (See fig. 50.) If meters are installed at large installations such as hospitals and
laundries, show their hourly consumption and subtract it from the gas company's hourly deliveries in order to determine the net amount delivered to the remainder of the system. Omit data on large installations if there are no meters; do not estimate.
b. Analyze results of test by plotting on graph paper the curves of the net hourly deliveries at the lower and higher pressures, and determine the amount of increase in delivery (leakage) due to the increase in pressure. This increase, if appreciable leakage exists, is usually most apparent during the hours of minimum flow, which usually occurs from midnight to 0300. If hourly loads show substantial fluctuation, judgment is reqired to eliminate such fluctuations from consideration in determining leakage. As a general rule, comparison of deliveries at the lower and higher pressures can be done best by averaging the hourly deliveries for corresponding hours during the two nights at the lower pressure, and plotting the resulting curve, then proceeding similarly for the two nights at the higher pressure.
c. After the hourly indicated increase in leakage has been determined from the above analysis, the amount of leakage at any desired gage distribution piessuie can lie calculated as in the example below.
				gas distribution system leakage TEST	1																							
				Hame and location of station							Test no		Tested by: Title					Reviewed by: Title				Date reviewed		1
	Hour		1st test day Distribution p Hourly de)iver		Date:		2nd test day	Date:	 Distribution pressure:	* Hourly delivery in cubic feet				3rd test day	Date: Distribution pressure:	* Hourly delivery in cubic feet					1th test day	Date:	 Distribution pressure:	2 Hourly delivery in cubic feet					Comparison of avg hourly cu ft delivery under each nressure cenrfitinn			
					ressure:	*																			
					in cubic feet																			
	From	To	Gas Co’s meter	Hosp	Other	Net delivery	Gas Co’s meter	Hosp	Other	Net delivery	Gas Co’s meter	Hosp		Other	Net del ivery	Gas Co’ meter	Hosp		Other	Net delivery	Net avg delivery		Di f f	
																					at psi			
	1900	2000																						
	2000	2100																						
	2100	2200																						
	2200	2300																						
	2300	2100																						
	2100	0100																						
	0100	0200																						
	0200	0300																						
	0300	0100																						
	0100	0500																						
	0500	0600																						
	Avg/Hour																							
	Show average gage distribution pressure for night test period.	Avg	cu	ft	per hour "Net Delivery"	at	 psi		 To be filled in only if meters are installedat these or other	Avg	cu	ft	per hour "Net Delivery"	at	 psi		 large installations operating at night. Do not estimate.	Avg	cu	ft	per hour difference List installations included in Other* column, such as laun-	Cu ft per	hour leakage at	 psi		 dry, bakery, etc:	Avg	cu	ft	leakage/mile of pipe/year at	 psi		 	—	—	 Avg cost of leakage/mile of pipe/year at		psi 	 Remarks:			.	 Leakage cost based on avg gas cost/mcf of		 Based on data for following time period:																									
																								
Figure 50. Leakage test form.
61
which is based on the assumption that leakage varies directly with the gage distribution pressure:
Gage distribution pressures during leakage test:
11 psi and 19 psi.
Increase in leakage indicated by test: 320 cubic feet per hour.
Amount of leakage per pound of increase in gage
320
distribution pressure =----------= 40 cubic feet
19—11
Amount of leakage at 15 psi
gage distribution pressure = 15 X 40 = 600 cubic feet per hour.
per hour.
Note. The pressure-change method of running leakage tests is not applicable to low-pressure distribution systems.
62
APPENDIX IV
GAS DISTRIBUTION SYSTEM LEAKAGE TESTS ON INTERMEDIATE- AND LOW-PRESSURE SYSTEMS BY METERING-IN AND PRESSURE-DROP METHODS
1.	Application
The metering-in and pressure-drop methods for leakage tests are used in testing entire systems for leakage. However, since both methods require that all points of consumption in the test area be shut off, these methods are used primarily for leakage tests on sections of the system. In order to have leakage control with minimum labor and expense, it is necessary to locate the sections of the system in which excessive leakage exists.
2.	General Procedure
a.	The first two steps, which are common to both methods, are as follows:
(1)	1 urn off all points of consumption in the section under test by closing valves at each piece of gas-burning equipment and by closing the valve on each service line outside the building.
(2)	Turn off all distribution valves at the boundary of the section under test in order to isolate that section completely from the remainder of the system. On low-pressure systems, use gas stoppers for this purpose if distribution valves have not been installed in sufficient number or are not correctly located for this test.
b.	The accuracy of these tests requires that the distribution valves give a positive shut-off. Lubricate plug valves immediately before the test. After turning off all valves in the section to be tested, check for leakage into the test section by blowing it down and noting whether the pressure builds up in the test section. If no such leakage is indicated, within a few minutes the section is ready to be tested.
c.	Test all sections at the same distribution pressure to obtain comparable results. Do not use a test pressure in excess of the maximum normal distribution pressure carried on the system.
3.	Metering-In Method
a.	Follow procedure described in paragraph 2.
b.	Install bypass line at one of the boundary distribution valves by tapping the gas line immediately upstream and downstream of the valve, and install a positive meter and indicating pressure gage in the bypass section to measure all gas entering the section being tested. Usually a small, domestic type positive meter has enough capacity for the test if its working pressure is not exceeded.
c.	During the test, hold the pressure constant on the distribution system and in the test section. If the distribution pressure fluctuates slightly during the test, correct it by stopping the test at a time when the pressure at the meter is the same as the initial pressure.
d.	Read the meter index and the pressure gage at the beginning and end of the test period, and read the pressure gage at 15-minute intervals during the test in order to obtain the average gage pressure. Since the rate of flow is usually too small to get an accurate reading from the index, compute it at frequent intervals by timing the revolutions of the index test dial hand. The meter index test dial is usually marked either 1, 2, 5, or 10. This means that the meter passes that number of cubic feet at indicated gage pressure each time the test hand makes one revolution. The amount of gas represented by the revolutions of the test hand should be corrected by applying a pressure multiplier to the average amount of gas passed during the average reading period. To find the pressure multiplier, add the average gage pressure during the test to the atmospheric pressure and divide by the measurement base pressure applicable to the post.
e.	If the pressure in the test section remains constant and if there is no leakage through the distribution valves at the boundary of the section, average hourly amount of gas entering the section through the positive test meter equals the hourly leakage out of the test section.
f.	After finding hourly leakage for the test section
63
by the method used in the example, table VII. place the leakage of the section on a basis comparable with other test sections by calculating the cubic-foot-per-hour leakage per 1,000 feet of 3-inch equivalent by the method in (2) of the example, table VIII.
Table VII. Gas distribution shut-in
g.	The mctcring-in method has the following advantages over the pressure-drop method:
(1) It gives a more positive measurement of leakage, particularly where common gages are used in the pressure-drop test.
leakage tests by metering-in method
Example
Measurement pressure base =14.4 psi 4-8 oz. = 14.9 psi absolute.
Atmospheric pressure — 14.4 psi.
Location of test section: Section B (see gas distribution system map).
Test started at: 1415. Test ended at: 1630. Date: 14 May 1945.
Time	Meter i ndex reading	Test dial '2 c:i L			Gage pressure (psi)
		Rev			
			Min		
1415 1430 1445 1500 1515 1530 1545 1600 1615 1630		10 10 10 10 10 10 10 10 10 10	6 6 6 6 6 6 6 6 6 6	40 33 42 41 38 39 37 43 42 38	9.0 9.2 9.0 8.8 8.9 9.0 9.2 9.1 9.0 9.0
		10	6	39.3	9.02
1. Average time to pass 20 cubic feet (10 X 2) — 6 minutes 39.3 seconds — 6.635 minutes.
Metered volume = (2 X 10) X •——— = 180.3 cubic feet per hour.
6.boo
14-4 + 9.02	,
Pressure multiplier = --------------■ = 1.5718.
Cubic feet per hour leakage (at base pressure) = 180.3 X 1.5718 = 283.4.
2. Convert to cubic feet per hour leakage per 1,000 feet of 3-inch equivalent as in (2), table VIII.
Table VIII. Intermediate-pressure system gas distribution shut-in leakage tests by pressure-drop method
(1) Nominal Size	(2) Actual diameter		(3) Cubic foot per hour loss per pound pressure drop per minute per hundred linear feet*	(4) Multipliers to convert to linear feet of 3-inch equivalent
	OD (inches)	ID (inches)		
Vi	0.840	0.622	0.85	0.240
	1.050	0.824	1.49	0.300
i	1.315	1.049	2.42	0.376
VA	1.660	1.380	4.18	0.474
VA	1.900	1.610	5.69	0.543
2	2.375	2.067	9.38	0.679
DA	2.875	2.469	13.39	0.821
3	3.500	3 068	20.67	1.000
4	4.500	4.026	35.60	1.286
5	5.563	5 047	55.95	1.589
6	6.625	6 065	80.79	1.893
8	8.625	8.071	143.07	2.464
10	10.750	10.192	228.14	3.071
12	12.750	12.090	321.02	3.643
* Losses based on the assumption that gas temperature remains constant.
(2) The test period can be shorter for the same degree of accuracy.
(3) It minimizes the effect of leakage through the closed distribution valves, since the distribution pressures in the test section and in the balance of the system are the same.
Example
1. Section tested:
350 feet of 2-inch pipe	Length of test: 90 minutes.
470 feet of 3-inch pipe	Initial gage pressure: 25.0 psi.
520 feet of 4-inch pipe	Final gage pressure: 18.5 psi.
Pressure drop: 6.5 psi.
Loss: See column (3).
Note. If mercury-filled manometer is used for test, multiply
pressure drop in inches of mercury by 0.49 to convert to psi before
substituting in equation.
Cubic feet per hour leakage
_ (3.5 X 9.38 + 4.7 X 20.67 + 5.2 X 35.60) X 6.5 psi
90 minutes
— 22.76 cubic feet per hour leakage.
2. Use column 4:
Number of linear feet of 3-inch equivalent in section:
350 feet X 0.679 = 238 feet
470 feet X 1.000 = 470
520 feet X 1.286 = 669
1,577 feet of 3-inch equivalent.
Cubic feet per hour leakage per 1,000 feet of 3-inch equivalent 22.76
— --------— 16.53 cubic feet per hour.
1.377
64
4.	Pressure-Drop Method
a.	Follow procedures set forth in paragraph 2.
b.	Open one of the closed valves and allow the pressure in the section to equalize with the balance of the distribution system. Then close valve again.
c.	Allow a few minutes for the pressure throughout the test section to equalize before starting the test.
d.	Install an accurate indicating pressure gage or mercury manometer in the test section if system is on intermediate pressure. Install a water-filled manometer if system is on low pressure.
e.	Record the exact time and the pressure on the section at the start and end of the test period. Do not allow pressure on a low-pressure system to drop lower than 3 inches of water.
f.	With the above data and the lengths and sizes of all pipe in the test section, it is possible to compute the leakage rate of an intermediate-pressure drop by using table VIII, and of a low-pressure system, by using table IX.
Table IX. Low-pressure system gas distribution shut-in leakage tests by pressure-drop method
(1) Nominal size	(2) Actual diameter		(3) Cubic feet per hour less per inch water cilumn pressure drop per minute per 100 linear feet	(4) Multipliers to convert to linear feet of 3-inch equivalent
	OD (inches)	ID (inches)		
	0.840	0.622	0.031	0.240
%	1.050	0.824	0.054	0.300
i	1.315	1.049	0.087	0.376
	1.660	1.380	0.151	0.474
iH	1.900	1.610	0.205	0.543
2	2.375	2.067	0.338	0.679
2n	2.875	2.469	0.482	0.821
3	3.500	3.068	0.744	1.000
4	4.500	4.026	1.282	1.286
5	5.563	5.047	2.014	1.589
6	6.625	6.065	2.908	1.893
8	8.625	8.071	5.150	2.464
10	10.750	10.192	8.213	3.071
12	12.750	12.090	11.557	3.643
Example
Part I. (Use Column C.)
Section tested:
3,400 feet of 1%-inch pipe Length of test: 30 minutes.
4,370 feet of 2-inch pipe Initial gage pressure: 9 inches water column.
5,150 feet of 4-inch pipe Final gage pressure: 3 inches water column.
Pressure drop: 6 inches water column.
Cubic feet per hour leakage
(34 X 0.205 + 43.7 X 0.338 + 51.5 X 1.282) X 6 inches
30 minutes = 17.53 cubic feet per hour leakage.
Part II. (Use Column D.)
. Number of linear feet of 3-inch equivalent* in section:
3,400 X .543 = 1,846
4,370 X .679 = 2,967
5,150 X 1.286 = 6,623
11,436 feet of 3-inch equivalent.
Cubic feet per hour leakage per 1,000 feet of 3-inch equivalent 17.53 •
= ------- =1.53 cubic feet per hour.
11.436
g.	There can be no set length of test period for all sections. On sections with little leakage, test periods will be necessarily longer to get a large enough pressure drop for accurate reading of the pressure instrument.
h.	After finding hourly leakage for the test section by the method used in (1), examples, tables VII and VIII, place the leakage of the section on a basis comparable with other test sections by calculating the cubic-foot-per-hour leakage per 1,000 feet of 3-inch equivalent by the method shown in (2) of the examples, table VIII.
i.	The advantage of the pressure-drop method over the metering-in method is that the labor and expense of installing a bypass line and a positive meter is eliminated.
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