3A1. General. In submarines as in all ships, a certain amount of water from various sources accumulates inside the hull. The most important of these sources include:

1. Leakage at-glands around the propeller shafts, pitometer log, sound gear, periscopes, and similar equipment.

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

3. 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. Reference to the general arrangement shown in Figure 3-9 will be helpful in understanding the functional description which follows.

3A2. Functional description. The drain pump, located in the pump room, provides 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, usually called the drain line forward and the drain line aft. The drain line forward and the drain line aft can be cut off by shutting their respective stop valves, located in the pump room.

In Figure 3-9, proceeding forward from the pump room, it an be seen that the drain

  line forward extends to the forward torpedo room and provides pumping connections for the two bilges and the pitometer 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 contains also a suction line to the collecting 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 from the three pump room bilge sumps.


Figure 3-1. Drain pump.
Figure 3-1. Drain pump.

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) the overboard discharge; 2) the compensating water main; and 3) the trim system. In addition, the drain pump is so interconnected with the trim manifold that it can discharge water into the trim system instead of into its own piping. This interconnection 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. The required discharge valves are then opened to the overboard discharge, the compensating water main, or the trim system, depending

  upon the conditions. Then the drain pump is started and the pumping begins. When 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.

Bilge water should not be discharged directly overboard if there is danger of detection by the enemy, because the oil in it will rise to the surface, indicating the presence of the submarine. Instead, bilge 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. But this may be a hazard to security, because discharging variable tanks to sea during trimming operations will allow bilge oil to rise to the surface, leaving the telltale oil slick.

3B1. Source of power. An electric motor, rated at 10 horsepower and 1150 revolutions per minute, is used to drive the drain pump through-a worm and worm gear assembly as shown in Figure 3-1. The two types of pumps in use are shown in this illustration. One has a vertically mounted motor and is shown in the large cutaway view; the other has the "motor mounted horizontally and is shown in the upper left-hand corner of Figure 3-1. The cutaway view shows the mechanical construction of the pump.

3B2. 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 vacuum, or suction. This lowered pressure

  "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 discharge. When the plunger reaches the end of its stroke, expansion of this 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.

3B3. Lubrication. Lubrication of the main bearings and the connecting rod bearings is accomplished by the multiple oiler mounted on the pump casing. Oil reaches the bearings through 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.

3B4. Relief Valve. The relief valve, set at 225 pounds per square inch, is mounted on the pump body and protects the pump from excess 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.

3B5. The drain pump controls. The electrical controls for the drain pump consist of the motor switch, the air chamber pressure

  indicators, and the control panel. All 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 which is ON when the motor is running.

The drain pump control panel is housed in a ventilated panel box with a removable door. This panel supports the contactors, relays, fuses, and overload relays of the control circuit.

The air chamber pressure indicator consists of two lights which show the conditions existing in the pump air chambers. They are controlled by a limit switch mounted in the air chamber. If too much water is in the chambers, both lights will be ON. In this case air should be blown into the chambers until one light goes OUT. If both lights are OUT, insufficient water is in the chambers, and they must be vented until one light goes ON.

Figure 3-2. Drain pump controls.
Figure 3-2. Drain pump controls.

Figure 3-3. Drain line stop valve.
Figure 3-3. Drain line stop valve.

3C1. Drain line stop valves. In Section 3A it was explained that the suction of the drain pump could be applied to either the forward or the after drain line. 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. These two 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 (see Figure 3-9).

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, the construction of which is shown in Figure 3-3.

Opening the forward drain line stop valve by its manually operated handwheel places the forward drain line on SERVICE and permits the use of the forward section of the drain system. Similarly, the after drain line stop valve is used to place the after drain line on or off SERVICE.

3C2. 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 a passage for the drain water.

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 (see Figure 3-4). 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.

The mechanical details of the drain pump overboard discharge valve are shown in Figure 3-4. The valve is mounted with the outboard leg extending through the pressure hull; the midway flange is bolted and gasketed to the hull to insure a pressure-tight connection. The threaded flange is connected to the pipe leading overboard. The flange on

  the inboard leg of the valve is connected to the stop check valve on the line leading to the drain pump discharge. The bolted bonnet gives access to the disk and seat valve for inspection and repair. The adjustable packing gland prevents leakage around the rising stem when the valve is subjected to depth pressure.

When discharging from the drain pump to sea, the manually operated overboard discharge valve must be opened. It is shut immediately after the discharging operation is completed.

3C3. Bilge strainer. Although the purpose of the bilges is to collect excess water, 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. As a precaution, each bilge sump is equipped with a bilge strainer (Figure 3-5) which-screens the bilge water before it enters the drain system lines, and holds back any large particles.

The three bilge sumps in the forward torpedo room, the three in the pump room, the two in each engine room, the one in the motor room, and the two in the after torpedo room are equipped with bilge strainers of the general type shown in the illustration. The only exception is the after bilge sump in the after torpedo room which is equipped with a Macomb strainer. The size and shape of the strainers vary somewhat to suit the individual bilge sumps.

The strainer consists of an open-bottom mesh cylinder set in the bilge sump. The mesh is held in place by clips screwed to chocks which are welded to the pressure hull. The top cover is split and has hinged sides. It is held tightly closed around the bilge suction pipe by a holding spring.

The bilge water enters the strainer through the screen, which holds back all large particles of solid material; the water drops into the well and is sucked into the drain system through the drain pipe. To remove foreign matter which may collect in the well,


Figure 3-4. Drain pump overboard discharge valve.
Figure 3-4. Drain pump overboard discharge valve.

Figure 3-5. Bilge strainer.
Figure 3-5. Bilge strainer.

Figure 3-6. Malcomb strainer.
Figure 3-6. Malcomb strainer.

Figure 3-7. Drain line sight glass.
Figure 3-7. Drain line sight glass.
the hinged covers may be opened by slipping off the holding spring.

3C4. Macomb strainer. Although the bilge strainers will prevent pieces of solid material larger than a half-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.

Figure 3-6 illustrates the construction of a typical Macomb strainer. The shape of the body and the position of the inlet and outlet ports vary somewhat in individual cases to suit conditions of space or use.

The strainer is connected into the drain suction line in such a manner that bilge water flowing therein will enter the inlet port and pass through the wire mesh basket before leaving by the outlet port to continue on to the drain pump.

  The wire mesh basket permits water to flow freely from inlet to outlet but traps and retains all solid matter larger than the holes in the wire mesh. The perforated plate basket serves to support and protect the wire mesh basket to which it is attached. The entire basket assembly can be removed for cleaning. The basket handle is used both for lifting and for holding the basket securely in place against the shoulder inside the body.

To clean the strainer, it is necessary to loosen the handle bolt, withdraw the self-locking toggle pin, and swing back the hinged yoke. The cover can then be lifted off using the ring provided, and the basket lifted out and cleaned. The reverse procedure is used in replacing and closing the strainer. After the yoke has been secured, the handle bolt is screwed down tightly to provide a leak-proof fit between the body and the cover. A plug is provided at the bottom of the body for draining.


Figure 3-8. Pitometer log well suction line and sump.
Figure 3-8. Pitometer log well suction line and sump.

There are three Macomb strainers in the drain system: one is connected into the drain pump suction line in the pump room; an other is connected into the collecting tank drain line in the after engine room; and the third is in the after torpedo room on the drain line running from the bilge to the after bilge manifold.

A fourth Macomb strainer is used in the trim system. It is located on the trim pump suction line in the pump room and is used to protect the trim pump from debris in the water ballast.

3C5. Drain line sight glass. The drain line sight glass (Figure 3-7) provides a means of determining visually the amount of oil or 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 to allow inspection of the water in the drain line.

The glass windows are protected by caps which screw onto the body of the fitting, protecting the glass from damage. The covers are attached to the fitting by bead chains

  and are provided with squared heads to fit the wrench used in removing them.

In use the cap is removed and the fluid in the drain line is visible through the sight glass. If more light is needed, the cap on the other side of the drain line may be removed and an external light flashed through the fluid in the line to the sight side.

There are two drain line sight glasses, one on the suction line near the drain pump strainer in the pump room, and the other in the after engine room on the collecting tank drain line.

3C6. Pitometer log well suction line and sump. The water which collects in the pitometer log well is pumped out by the pitometer log well suction line. This line extends from the main drain line and runs athwartship along the after bulkhead of the forward torpedo room to the pitometer log well.

It is equipped with a bilge strainer which is fitted into the well. A stop check valve mounted in the line between the well and the forward drain line (see Figure 3-8), is opened to pump the pitometer log well.



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