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10
TRIM AND DRAIN SYSTEMS
 
A. TRIM SYSTEM
 
10A1. General description. As explained in Chapter 5, the balance and stability of the submarine can be upset by an unequal distribution of weights in the ship. The trim system is employed chiefly to correct this condition by regulating the quantity of water in the variable tanks.

FigureA-12 illustrates the general arrangement of the trim system in the submarine. It shows the trim pump manifold, the main flood and suction lines, the valves, and the connections to the various trim system tanks.

The trim manifold, located on the port side aft in the control room, is the center of control for the entire system in that it directs the flow of water to the various tanks. It is a casting divided into two longitudinal compartments known as the suction and discharge sides. The discharge side of the manifold contains eight discharge control valves. One of these valves is the trim pump discharge valve and connects the discharge side of the manifold with the discharge side of the trim pump. The suction side of the manifold contains eight suction control valves, and is connected to the suction side of the pump through the trim pump suction valve.

The remaining seven discharge and seven suction valves control the flood and suction from the following lines:

1. Trim pump suction and overboard discharge line.
2. Trim line forward flood and suction.
3. Trim line aft flood and suction.
4. Auxiliary ballast tank No. 1 flood and suction.
5. Auxiliary ballast tank No. 2 flood and suction.
6. Negative tank flood and suction.
7. Safety tank flood and suction.

The trim lines forward and aft serve the two trim tanks and the two WRT tanks, while auxiliary ballast tanks No. 1 and No. 2 are served by their own flood and suction

  lines; all of these tanks make up the variable ballast tanks group. The remaining flood and suction lines are connected to the negative and the safety tanks, called the special ballast tanks.

Cross connection of the trim pump and the drain pump is made by two flanged connections on the after end of the longitudinal axis of the manifold. One connection is on the discharge side, the other on the suction side.

The trim pump, located in the after end of the pump room, provides pumping power for the system. It draws water into its suction side, through the suction side of the manifold, from the tank being pumped, and discharges it through its discharge side into the discharge side of the manifold, which directs the water to the tank being filled. When it is desired to pump to one of these tanks by means of the trim pump, the discharge valve on the trim pump manifold controlling this particular tank is opened. When water is to be removed from a tank by means of the trim pump, its valve on the suction side of the manifold is opened. Thus, the trim manifold control valves serve to put any part of the trim system on suction or discharge. For example, in pumping from forward trim tank to after trim tank, the water is drawn through lines from the forward trim tank through the suction side of the manifold and into the suction side of the trim pump, and forced by pump action through the discharge side of the trim pump, through the discharge side of the trim manifold, and then through lines into the after trim tank. The trim line forward is a 3-inch line extending from the trim manifold in the forward torpedo room. The forward trim manifold controls the flooding and pumping of the forward trim tank and the forward WRT tank.

The trim line aft is also a 3-inch line, terminating in the after torpedo room at the after trim manifold, which controls the flooding

 
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and pumping of the after trim tank and the after WRT tank.

The Nos. 1 and 2 auxiliary ballast tanks are piped directly to their suction and discharge valves on the trim pump manifold. The flooding or pumping of these tanks can be accomplished only through the trim manifold. On the other hand, the flooding and draining of the safety and the negative tanks can be accomplished in two ways: either by the use of their suction and discharge valves on the trim manifold, or directly from sea by use of their flood valves. In the latter case, the blowing is accomplished by opening the flood valves and admitting compressed air into the tanks, thus forcing the water out; while the tanks are flooded by opening both the flood and the vent valves, allowing the sea to enter directly into the tanks.

The trim pump suction and overboard discharge line, connecting the trim manifold with the sea, provides the trim system with an overboard discharge to, or direct flooding from, the sea. In addition to the suction and discharge valves on the trim manifold, this line has also a sea stop valve and a magazine flood valve. The sea stop valve is used to shut off the sea from the trim system and the magazine flood valve. The magazine flood valve guarantees, when the sea stop valve is open, an immediate source of sea water to the ammunition stowage and the pyrotechnic locker.

As stated before, the main function of the trim system is to shift and adjust the distribution of weight throughout the submarine. This is done by means of transferring

  water ballast from one variable tank to another, adding water to the variable tanks or discharging excess water from the tanks overboard. Therefore, the water handled by the trim system is measured in pounds; and a gage, graduated in pounds to show the amount of water transferred by the trim pump, is located above the trim manifold where the operator can observe its reading.

Because the trim pump used on the latest fleet type submarine is of the centrifugal type, it must be primed before beginning the operation. A priming pump is used for this purpose. It primes the trim pump by removing all air from the trim pump casing, the trim manifold, and the lines leading to it, thus allowing water to replace the air in this equipment and fill it completely. It should be noted that some submarines are equipped with a trim pump of the reciprocating or plunger type, similar to the drain pump shown in Figure 10-5.

The trim system can also be used to supply or drain water from the torpedo tubes. Water for flooding torpedo tubes is normally taken from the WRT tanks through tube flood and drain lines. These lines are controlled by the torpedo tube flood and drain valves.

The trim line forward and the trim line aft are provided with hose connections, one in each compartment of the submarine. These connections can be used for fire fighting, or for bilge suctions in those compartments that do not have bilge suction facilities. Of course, if the connections are used for bilge suction the trim line must be on suction, and if for fire fighting, the line must be on discharge.

 
B. TRIM PUMP
 
10B1. Source of power. The trim pump, Figure 10-1, located on the port side of the pump room just forward of the after bulkhead, is driven by a 10/25 horsepower motor directly connected by means of a flexible coupling to the drive shaft of the trim pump.

The controller relay panel for the motor is mounted on the after bulkhead of the pump

  room. However, the motor is started or stopped by push button controls in the control room. Once started by these controls, the speed of the pump and, thereby, the rate at which water is moved in the system, is regulated by a rheostat control, also located in the control room just below the push button switch (Figure 10-2).
 
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Drawing of trim pump
Figure 10-1. Trim pump.
 
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Photo of trim pump controls.
Figure 10-2. Trim pump controls.
While the trim pump is driven by an electrical motor, the starting of the motor does not guarantee that the trim pump will pump water, for the trim pump, being of the centrifugal type, cannot pump air. Therefore, it cannot be operated until the system is free of air.

10B2. Priming pump. Freeing the system of air is the purpose of the priming pump, located outboard of the trim pump. Since any appreciable amount of air entering the inlet side of the trim pump will cause it to lose suction and thereafter run without pumping, it is necessary to know when this critical condition has been reached. To indicate the amount of air in the trim system a vacuum gage is provided which is mounted in the control room. When the vacuum gage indicates less than 21 inches of vacuum, the priming pump must be operated before the trim pump is started. The priming pump, like the trim pump, is started by push button controls located in the control room. The

  priming pump is a vacuum pump with a float valve in the line, running from the priming pump to the trim manifold and the trim pump casing. The valve consists of a float with a ball-ended stem. The purpose of the float is to permit the passage of air and to prevent the passage of water into the priming pump. As the water rises in the float valve, the upper part of the ball-ended stem is automatically forced against the valve seat, thus preventing the sea water from entering the priming pump.

The priming pump is a self-priming centrifugal displacement pump consisting of three major parts: rotor, lobe, and port plate. The rotor is made up of a series of curved plates projecting radially from the hub. The lobe is elliptical in shape and forms the outer casing for the rotor. The port plate consists of two inlet and two outlet ports corresponding to the inlet and outlet ports on the rotor. The pump is end-mounted on the direct driving electric motor as shown in Figure 10-3.

 
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Drawing of priming pump.
Figure 10-3. Priming pump.
 
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Before starting the priming pump, it is necessary first to provide seal water to it. This water is needed to fill the lobe partly and provide a water seal. Water obtained from the seal water tank should be added until the seal water gage shows two-thirds full. (See Figure 10-3.) Serious damage may result if the pump is allowed to run in a dry condition. The motor is then started by the push button control in the control room.

In operation, the rotor revolves in the lobe, which has been partially filled with water, at a speed high enough to throw the water out from the hub by centrifugal force. This results in a solid elliptical-shaped ring of water revolving at the same speed as the rotor. In Figure 10-3, showing rotor operation, it may be seen that a ring of water for a given rotor section, guided by the lobe, will move in and out from the hub, forming a liquid piston. As the rotor passes the inlet port, the water ring is farthest from the hub, and air is permitted to enter. As the rotor advances to discharge port, the air space becomes less and air is forced out the discharge port. This cycle is repeated twice for each revolution of the rotor. When the vacuum gage registers 21 inches of vacuum in the trim system, the priming pump can be stopped and the trim pump started.

10B3. Operation of the trim pump. A brief review of the general principles of centrifugal pumps will be helpful in understanding the operation of the trim pump. As the name implies, this type of pump employs centrifugal force to move a liquid from a lower to a higher level. In its simplest form, the centrifugal pump consists of an impeller rotating in a watertight casing provided with inlet and outlet ports.

The impeller consists of two parallel disks with curved vanes or bulkheads radiating from the hubs and between the disks. One of these two disks (upper or lower, depending upon where the water is brought in) has an inlet port or circular opening called the eye, concentric with the hub of the impeller. Actually then, one disk holds the impeller to the shaft while the other admits the water.

  The periphery of the impeller is open, as shown in Figure 10-1.

In operation, water enters the eye of the impeller, is picked up by the vanes and accelerated to a high velocity by the rotation of the impeller, and discharged by centrifugal force into the casing and out of the discharge port. When water is forced away from the eye of the impeller, a suction is created and more water flows in. Consequently there is a constant flow of water through the pump. An air bubble in the inlet port of the pump will interrupt the action of the pump since it will, upon entering the impeller, break the suction at the eye which is dependent on the presence of water. For this reason, the pump casing and the system served by the pump must be solidly filled with water before pumping is commenced. This is the function of the priming pump. The centrifugal pump described above has only one impeller and is known as a single-stage pump; a pump with four impellers would be known as a four-stage pump; with six impellers, a six-stage, and so on. In practice however, any pump with more than one stage is referred to as a multi-stage pump.

The mechanical details of the trim pump are shown in Figure 10-1. It will be seen that it is a six-stage centrifugal pump. The valve shown on the forward end permits either parallel or series operation and is manually operated. The schematic diagram in the upper right corner of the illustration shows the flow of the water being pumped for both series and parallel operation. With the manually operated series-parallel valve in the SERIES position, the incoming water enters the first stage, proceeds through the second and third stages, and then back through the series-parallel valve to the fourth, fifth, and sixth stages. With the series-parallel valve in the parallel position, half of the inlet water proceeds through the first, second, and third stages, and is then discharged through the series-parallel valve. Simultaneously, the other half of the inlet water is directed by the series-parallel valve to the fourth, fifth,

 
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and sixth stages and is then discharged directly. Series operation of the pump produces twice the discharge pressure, but only one half the volume produced by parallel operation. The pump is operated in series only when the submarine is at depths of approximately 250 feet or more and discharging to the sea, the higher pressure being necessary to overcome the greater sea pressure encountered at that depth.   not be started if this gage registers less than 21 inches of vacuum. If the gage shows less than 21 inches, the system must be restored to the proper condition by using the priming pump. When the gage registers the required 21 inches, the priming pump is stopped and the trim pump started.

The trim pump should not be operated at speeds greater than are necessary to produce a rate of flow specified for a given depth. The accompanying table lists the valve

DEPTHPUMP OUTPUTVALVE POSITION
On surface1,500-2,500 pounds per minuteParallel
0-200 ft.1,500 pounds per minuteParallel
200-250 ft.1,250 pounds per minuteParallel
400 ft. or deeper1,000 pounds per minuteSeries
250-400 ft.1,000 pounds per minuteSeries
To summarize, it must be remembered that before starting the trim pump, it is necessary to make certain that the trim system lines and the pump casing are free of air, as explained earlier in this section. A vacuum gage is provided to indicate the condition existing in the system. The trim pump must   position and pump output in pounds of water per minute, recommended at different depth levels.

The pump should not be operated at a motor speed greater than 2,400 rpm. Excess speeds place an overload on the bearing and mechanical parts of the pump and may cause a breakdown.

 
C. MANIFOLDS
 
10C1. Trim manifold. In section A of this chapter, the trim manifold is referred to as the center of distribution for the trim system. It acts as a switchboard between the trim pump and the lines of the system, providing a centralized station to direct the flow of water to and from the variable tanks. Used in connection with the trim manifold, but connected to each variable tank, is a measuring gage, or liquidometer. These gages record the amount of water in each tank, and provide the diving officer with an indication of the amount of water ballast being redistributed by the trim manifold through the trim system. The trim manifold is mounted hip-high of the port side of the control room just forward of the after bulkhead, with the gage   board mounted directly above it.

Figure 10-4 shows the mechanical construction of the trim manifold, and also the proper nomenclature of its details.

It will be seen that the manifold is a box-like, two-piece casting divided internally into two longitudinal compartments, known respectively as the suction and discharge sides. The suction side contains eight suction control valves, while the discharge side has eight discharge (or flood) control valves. Each of these 16 valves is of the dish and seat type, with rising stems and individual bolted-on bonnets. Name plates attached to each bonnet indicate the function of that particular valve.

 
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Drawing of trim manifold
Figure 10-4. Trim manifold.
Starting from the after end outboard of the trim manifold, the valves in the suction   and discharge sides control the following components:
OUTBOARD (Suction)INBOARD (Discharge)
1. Trim pump suction9. Trim pump discharge
2. Auxiliary ballast tank No. 2 suction10. Auxiliary ballast tank No. 2 discharge
3. Auxiliary ballast tank No. 1 suction11. Auxiliary ballast tank No. 1 discharge
4. Safety tank suction12. Safety tank discharge
5. Negative tank suction13. Negative tank discharge
6. After trim line suction14. After trim line discharge
7. Forward trim line suction15. Forward trim line discharge
8. Sea suction16. Discharge to sea
The discharge valves are all on the starboard side of the manifold with the corresponding suction valves opposite them on the port side. A special wrench is provided for operating the valves.

Flanged outlets are cast integral with the manifold to connect with the lines of the system. Two outlets on the after end lead to the drain line cross connection and to the drain pump discharge to permit emergency use of the drain pump to actuate the trim system.

In all pumping operations, the trim pump suction and the trim pump discharge valves on the manifold must be opened to permit flow within the system. To flood a tank, the discharge valve for that tank must be opened at the trim manifold; to pump a tank, its suction valve must be opened. This should be done before the trim pump is started. All valves on the manifold should be shut immediately after the pumping operation is complete. Figure 10-4 shows the direction of flow when flooding or pumping auxiliary ballast tank No. 2.

10C2. Forward and after WRT and trim tank manifold. The WRT and trim tank manifolds are used in conjunction with the trim manifold to control the flooding and pumping of thre WRT tanks and the trim tanks, both fore and aft.

The forward trim manifold is located in the forward torpedo room, portside, aft, of the torpedo tubes. The after trim manifold is located in the after torpedo room, portside,

  forward of the torpedo tubes. (See Figure A-12.)

The forward and the after WRT and trim tank manifolds are identical in operation and construction, differing only in the fact that they serve different tanks.

The body of each trim manifold is a two chambered casting containing two valves which control flood and suction of the WRT tank and the trim tank respectively. The after valve in the after torpedo room and the forward valve in the forward torpedo room control the trim tanks. The valves are of the disk and seat type with bolted bonnets. The connecting passage between chambers of the integrally cast valve casting allows either valve to be operated independently. The handwheels carry name plates designating the uses of the individual valves.

When open, the manifold valve marked trim tank flood and suction permits the flooding or pumping of the trim tank from or into the trim system when the trim line is on service.

The other valve, marked WRT tank flood and suction, permits the flooding or pumping of the WRT tank from or into the trim system when the torpedo tube drain stop valve to the WRT tank is open.

10C3. Torpedo tube drain manifold. In Section A of this chapter, the flooding and draining of the torpedo tubes were mentioned as functions of the trim system. These functions are controlled by the torpedo tube drain manifolds. Two of these manifolds are located in

 
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the forward torpedo room, each servicing three torpedo tubes; and two in the after torpedo room, each servicing two torpedo tubes.

The body of the torpedo tube drain manifold is a three-chambered casting, housing three cam-actuated plunger type valves, and provided with flanged outlets for connection to the trim system and to the torpedo tube drains. The cam mechanisms are

  attached to the back of the casting. Separate control levers and connections are provided for each of the valves.

Each, hand lever operates one cam through the action of its connecting rod and cam lever. In draining or flooding the tubes, the manifold valves are used in conjunction with the torpedo tube drain stop valve to the WRT tank which must be open when draining from the tubes to the WRT tank.

 
D. VALVES
 
10D1. Trim pump sea stop valve. When it is desired to discharge water ballast from any part of the trim system to sea, the trim pump sea stop valve must be opened, thus providing a passage from the trim manifold through the pressure and outer hulls to the sea. The same line is used to permit water to enter the system from the sea when additional water ballast is to be added. This valve is located on the port side of the control room, directly below the trim manifold. (See FigureA-12.)

10D2. Torpedo tube drain stop valve to the WRT tank. The torpedo tube drain stop valve to the WRT tank serves as a stop valve between the WRT tank and the individual torpedo tube drain valves.

There is a torpedo tube drain stop valve

  to the WRT tank in both the forward and the after torpedo rooms. Both of these valves are identical in function and construction.

10D3. Magazine flood valve and testing casting. The magazine flood valve and testing casting provide an emergency method of flooding the magazine compartment.

The magazine flood valve is used to control this emergency flooding system. The testing casting is used to check the magazine flood valve to make certain that it is ready for immediate use. Both the magazine flood valve and the testing casting are located in the control room on the magazine flood line of the trim system. The accessory box, containing the operating plug and wrench, is mounted directly above the testing casting.

 
E. DRAIN SYSTEM
 
10E1. Functions. In submarines, as in all ships, a certain amount of water accumulates inside the hull from various sources. The most important of these sources are:

a. Leakage at glands around propeller shafts, Pitometer log, sound gear, periscopes, and similar equipment.

b. Draining of air flasks, manifold drain pans, conning tower deck gun access trunk, and escape trunk.

c. Condensation from air-conditioning cooling coils.

This water drains off into the bilges and wells where a number of bilge sumps with strainers are provided, from which the bilge water can be pumped.

The bilge sumps and wells are pumped periodically to prevent the excess free water from overflowing the bilges and interfering

  with the operation of the submarine. This water is pumped out by the drain system which consists essentially of the drain pump and the piping connecting the pump with the sumps and other drainage points in the submarine. The general arrangement shown in FigureA-12 is used in the following functional description:

The drain pump located in the pump room provides the suction for the drain system. The pump is started and stopped by means of an electric push button switch located nearby in the pump room. The drain pump has a suction and a discharge connection. A suction line equipped with a strainer and a sight glass connects the suction side of the pump with the main forward and after drain lines, called the drain line forward and the drain line aft. The drain line forward

 
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and the drain line aft can be cut off by shutting their respective stop valves located in the pump room.

Proceeding forward from the pump room, we note that the drain line forward extends to the forward torpedo room and provides pumping connections for the two bilges and the underwater log well in the after section of the torpedo room. The drain line terminates at the forward bilge manifold with two valves controlling the suction from the poppet valve drain tank and the forward bilge.

The escape trunk drain opens into the forward torpedo room; the water drains directly onto the deck and eventually empties into the bilges.

There are no drain line connections in the forward battery compartment.

The drain line aft extends to the after torpedo room and contains pumping connections to the sumps in the compartments in the after section of the submarine. There are no drain line connections in the after battery compartment. The forward engine room has two bilge sumps connecting with the drain line aft through two individual lines. The after engine room also has two bilge sumps which connect to the drain line by means of two separate lines. In addition to the bilge sump pumping connections, the drain line aft also contains a suction line to the collection tank, making it possible for water from the collecting tank to be pumped out through the drain system.

There is one bilge sump in the motor room.

The drain line aft terminates in the after bilge manifold in the after torpedo room. Here, too, the manifold contains two valves, controlling suction from the forward and after bilge sumps.

Returning now to the pump room, the drain pump suction line carries a branch connection to the pump room bilge manifold. This manifold contains three valves controlling suction front the three pump room bilge sumps.

  The drain water from the gun access trunk, the cable trunk, the periscopes, and the antenna wells empties into the pump room bilge and collects in the sumps from which it is pumped when required.

The drain pump has three points to which it may discharge: 1) overboard discharge, 2) compensating water main, 3) trim system.

In addition, the drain pump is so cross connected with the trim manifold that it can discharge water into the trim system instead of into its own piping. This cross connection permits the use of either the drain pump or the trim pump with either the trim or the drain system, in the event that one of the two pumps is not in operating condition.

Every branch suction line to the bilge sumps has its own bilge stop valve. When it is desired to pump out certain bilge sumps or wells, the valves leading from them to the drain line and the pump are opened; then the required discharge valves are opened to the overboard discharge, the compensating water main, or the trim system, depending upon the conditions. The drain pump is then started and the pumping begins. After the pumping is completed, the pump is stopped and the valves to the various lines used in the operation are shut.

The drain system can discharge the bilge water directly overboard, into the expansion tank through the compensating water main, or into the trim system through the trim manifold.

Normally, bilge water should not be discharged directly overboard because the oil in it will rise to the surface, indicating the presence of the submarine. Instead, the water should be pumped into the expansion tank, where the water separates from the oil before being discharged overboard.

If the trim system is used to receive the bilge drainage, it is possible to pump this water into the variable ballast tanks. This should not be done normally, because discharging variable tanks to sea during trimming operations will allow bilge oil to rise to the surface, leaving the telltale oil slick.

 
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F. DRAIN PUMP
 
10F1. Source of power. An electric motor, rated at 10 hp and 1,150 rpm, is used to drive the drain pump through a worm and worm gear assembly as shown in Figure 10-5. There are two types of pumps used: one with vertically mounted motor as shown in the large cutaway view of Figure 10-5, and the other with the motor mounted horizontally as shown in the small illustration. The cutaway view shows the mechanical construction of the pump.

10F2. Description. The drain pump is a single-acting duplex reciprocating pump with the cylinders mounted vertically. The two plungers are connected to the crankshaft by connecting rods, so that one plunger completes its downward travel at the moment the other plunger completes its upward travel. As a plunger moves upward in the cylinder, it creates a vacuum (suction) which draws water into the cylinder through the valves from the inlet, or suction, port. When the plunger reaches the top of its stroke and starts its downward travel, the water forces the suction valve down, closing the inlet port, opening the discharge valve, and allowing the water to flow out of the discharge port. At the same time, the second plunger is performing the reverse operation, taking a suction, while the first plunger is discharging. This results in a continuous flow of water through the pump.

An air chamber is provided for each cylinder to smooth out the flow and quiet the pump operation by cushioning the discharge.

  Air in the chamber is compressed during the discharge. When the plunger reaches the end of its stroke, expansion of the air tends to keep the water flowing until the reverse stroke begins.

A connection is provided to the 225-pound air system for recharging the chambers. Indicator lights show when the chambers need charging or venting.

10F3. Lubrication. Lubrication of the main and the connecting rod bearings is accomplished by the multiple oiler mounted on the pump casing. Oil is led to the bearings by holes drilled through the crankshaft and connecting rods. The worm gear drive runs in oil, which is cooled by sea water circulating through a coil installed in the worm drive housing.

10F4. Relief valve. The relief valve, set at 225 psi, is mounted on the pump body and protects the pump from excessive pressure in case a valve is shut on the discharge line when the pump is operating.

A drain cock is provided to allow the draining of all water from the pump.

10F5. The drain pump controls. The electrical controls for the drain pump consist of the motor switch, the air chamber pressure indicators, and control panel. All of these are mounted on the port side of the pump room.

The motor switch is equipped with a push button for starting, a push button for stopping, and a signal light that is on when the motor is running. (See Figure 10-6.)

 
G. VALVES AND FITTINGS
 
10G1. Drain line stop values. The drain system is provided with two valves, known as the forward and the after drain line stop valves respectively. These valves will put either drain line on service, depending on which section of the boat is to be serviced. The valves are located on the port side of the pump room, forming the connection between the line leading to the suction side of the drain pump and the forward and after drain lines.   The forward drain line stop valve is an angle valve of the disk and seat type with a bolted bonnet, a rising stem, and flanges for connection to the lines. The after drain line stop valve is a globe valve.

10G2. Drain pump overboard discharge valve. When the water collected from the bilges by the drain system is to be discharged directly to the sea, two valves must be opened to provide passage for the drain water.

 
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Drawing of a drain pump
Figure 10-5. Drain pump.
 
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Photo of drain pump controls.
Figure 10-6. Drain pump controls.
The inboard valve is a stop check valve; the second valve is outboard of the first and is known as the drain pump overboard discharge valve. Both are located on the port side forward in the pump room, and are mounted in tandem so that the stop check valve acts as a sea stop for the discharge valve.

10G3. Bilge strainer. Although the purpose of the bilges is to collect excess water, a miscellany of solid material such as flakes of paint and bits of metal inevitably finds its way into the bilges. If this solid matter were to enter the lines of the drain system, it might clog or damage the drain pump. To prevent this, each bilge sump is equipped with a bilge strainer which screens the bilge water before it enters the drain system lines and holds back any large particles.

10G4. Macomb strainer. Although the bilge strainers discussed in Section 10-G3 will prevent pieces of solid material larger than 1/2 inch from entering the drain system, it is necessary to screen the water again to remove any smaller particles of debris that

  might clog or damage the drain pump. Such material is filtered out of the drain system by the Macomb strainers.

10G5. Drain line sight glass. The drain sight glass provides a means of visually determining the amount of oil of solid matter in the bilge water as it flows through the lines of the drain system. It consists of a cross-shaped casting, two ends of which are flanged and connected to the drain lines. The other arms are fitted with glass plates forming a window to allow inspection of the water in the drain line.

10G6. Underwater log well suction line and sump. The water that collects in the underwater log well is pumped out by the underwater log well suction line. This line extends from the drain line and runs athwartships along the after bulkhead of the forward torpedo room to the underwater log well.

It is equipped with a bilge strainer which is fitted into the well. A stop check valve is mounted in the line between the well and the forward drain line which is opened to pump the underwater log well.

 
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