HNSA Crest with photos of visitors at the ships.
Figure 2-1. HIGH-PRESSURE AIR SYSTEM.

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HIGH-PRESSURE AIR AND TORPEDO IMPULSE
AIR SYSTEM
 
A. GENERAL DESCRIPTION
 
2A1. Introduction. Figure 2-1 shows the location and relationship of the individual units that comprise the high-pressure 3000-pound air system. It must be noted that 3000 pounds is the maximum working pressure of the system and not a constant pressure; actually, the pressure may vary between 1500 and 3000 psi. The system is hydrostatically tested up to 4500 psi or 150 percent of the working pressure. The system extends from the high-pressure air compressors in the pump room to the receiving and distributing manifolds in the control room, and from there forward to the torpedo impulse air system in the forward torpedo room, athwartship to the air banks, and aft to the torpedo impulse air system in the after torpedo room.

In Sections 2A2 through 2A4, immediately following, a more detailed description of the general layout of the high-pressure air system is given. In Sections B through F of this chapter, component parts of the system are described and the function of each is explained.

Complete instructions for specific operations of the 3000-pound air system, and schematic drawings showing the flow of it within the system are given in Chapter 7.

2A2. Manifolds and lines. The high-pressure manifold (made up of a receiving manifold and two distributing manifolds) is mounted on the starboard side of the control room. The receiving manifold receives air from two high-pressure air compressors, and directs it to the air banks, where it is stored. As the air is needed, it flows back through the same piping to the receiving manifold, where it is directed to the distributing manifold. This operation is controlled by the valves on the manifold. (See Figure 2-2.)

The 3000-pound service air lines supply air at a pressure up to 3000 psi to the forward and after torpedo rooms and to the reducing

  valves and engine-starting flasks in each engine room. The reducing valves furnish engine-starting air at a pressure of 500 psi, either directly from the 3000-pound air service lines, or from the engine-starting flasks which store the air for use in starting the diesel engines.

The distributing manifolds distribute air to the safety and negative tank blow lines, the main ballast tanks blow manifold, the hydraulic accumulator air flask, the high-pressure air bleeder, the bow buoyancy tank blow line, the 225-pound service air system, and the forward and after 3000-pound service air lines.

2A3. Air banks. Each of the five air banks consists of seven flasks, with the exception of the No. 1 air bank, which has eight. Each flask is provided with a drain valve. The total capacity of the air banks is 560 cubic feet. The No 1 air bank is located inside the pressure hull, with four flasks in each battery compartment. The other four air banks are located in the main ballast tanks. (See Figure 2-1.)

2A4. Torpedo impulse air system. The torpedo impulse air system stores and controls the air used to discharge the torpedoes from the tubes in firing.

The 3000-pound air service line forward, extending from the distributing manifold, ends with a 3000-pound to 600-pound reducing valve, from which a line leads to the forward torpedo impulse air system. This system is composed of two impulse flask charging manifolds (Figure 2-1) and six impulse flasks, connected by lines to the manifolds. The impulse flasks are mounted above the pressure hull in the superstructure forward. One impulse flask charging manifold is located on the port side of the torpedo room and the other on the starboard side. Each manifold is used to charge three flasks with 600-pound air.

 
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Figure 2-2. High-pressure air manifold drawing.
Figure 2-2. High-pressure air manifold.
 
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The 3000-pound air service line aft, extending from the distributing manifold, ends with a 3000-pound to 600-pound reducing valve, through which air is furnished to the after torpedo impulse air system. This system consists of one impulse flask charging manifold with lines leading to the four impulse flasks provided for the four after torpedo tubes. The impulse flasks are mounted below the after torpedo room deck; the   manifold is located on the starboard side. (See Figure 2-3.)

In both the forward and the after sections of the torpedo impulse system, a bypass valve and line are provided, leading from the 3000-pound air service line to the charging manifold. The bypass valve and line allow the charging of the impulse flasks in the event of failure of the reducing valves.

 
B. HIGH-PRESSURE AIR MANIFOLD
 
2B1. Description. As explained in Section 2A2, the high-pressure manifold is used to direct the storage and distribution of air within the 3000-pound air system.

The high-pressure air manifold is mounted on the starboard side of the control room, with the valves facing inboard.

Pressure gages which indicate the pressure in each air bank and in the receiving manifold are mounted directly above the manifold.

Figure 2-2 shows the mechanical construction of the manifold. It is composed of one receiving manifold and two distributing manifolds, interconnected to allow air to flow through all three. The manifolds are in horizontal layers, one above another, with the receiving manifold at the bottom.

The receiving manifold has seven valves which control connections to the five air banks, the external charging connection, and the supply line from the high-pressure air compressors.

The lower distributing manifold has five valves which control connections to the two reducing valves of the 225-pound air system, the bypass line to the 225-pound air system, and the forward and after 3000-pound service lines. On some of the older fleet type submarines, there is an additional valve at each end of the lower distributing manifold which controls the supply of air from the receiving manifold to the distributing manifolds.

  The upper distributing manifold has seven ports which connect in sequence to the bow buoyancy tank blow valve, the high-pressure air bleeder valve, the air valve to the hydraulic accumulator, the negative tank blow valve, the supply valve to the 600-pound MBT blow manifold, the emergency supply valve to the 600-pound MBT blow manifold, and the safety tank blow valve.

The inset in Figure 2-2 shows the hammer valves (older type boats) which are the high-pressure blow for bow buoyancy, negative, and safety tanks in the lines between the high-pressure manifold and the above mentioned tanks. Note that this arrangement differs from the high-pressure manifold illustrated in Figure 2-2 where the hammer valves for blowing bow buoyancy, negative, and safety tanks are on the manifold itself.

Air at pressures up to 3000 psi is delivered by the compressors through the receiving manifold to the air banks where it is stored. As the air is needed, it flows back from the air banks to the receiving manifold. To place an air bank on service, the valve that controls that bank at the receiving manifold is opened. An air bank should be placed on service only if its pressure gage registers above 1500 psi.

When the submarine is rigged for surface, one air bank is on service. When it is rigged for diving, three banks are placed on service.

 
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Figure 2-3. After torpedo impulse charging manifold.
Figure 2-3. After torpedo impulse charging manifold.
 
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FIGURE 2-4. HIGH-PRESSURE AIR COMPRESSOR.

 
C. HIGH-PRESSURE AIR COMPRESSORS
 
2C1. Description. The air used in the 3000-pound air system is compressed by two high-pressure air compressors mounted in the pump room, one on each side of the centerline.

The air compressors are of the four-stage vertical type with a direct electric motor drive. Starting and stopping of the compressors are controlled by manually operated electric switches located in the pump room near the compressors. The mechanical details of the compressor and its accessory equipment are shown in Figure 2-4.

The major components of the high-pressure compressor are the cylinder blocks with compression stages or cylinders, the center frame which houses the crankshaft, and the base which supports the entire assembly and contains the first and second stage intercoolers.

The left-hand cylinder block consists of the third stage cylinder head and shell serving as a head for the left-hand first and second stage (differential) cylinder. The right-hand cylinder block is similar, except that the fourth stage cylinder head and shell form the head of the right-hand first and second-stage (differential) cylinder. Each differential cylinder (left- and right-hand) contains a differential piston operating both the first and second stages. There is one piston for the third stage and one for the fourth. The third and fourth stage pistons are of the built-up type and are attached to the top of the first and second stage (differential) pistons.

2C2. Compression stages. When the compressor is operating, air at atmospheric pressure enters through the top inlet port, passes through the strainer, muffler, and first stage suction valves, and enters the two first stage cylinders on the downward stroke. The upward stroke of the first stage piston compresses this air to 31-38 psi and forces it past the first stage discharge valves. This air passes through the first stage intercooler, giving up its heat of compression, and then through the second stage suction valves and the two second stage cylinders on the upward stroke.

  On the downward stroke of the two second stage pistons the air is compressed to a pressure of 170-185 psi and is forced past the second stage discharge valves. This air passes through the second stage intercooler, giving up its heat of compression for that stage.

The air then enters the third stage through its suction valves, on the downward stroke of the third stage piston. On the upward stroke of the third stage piston, this air is compressed to 800-860 psi and is forced past the third stage discharge valves. This air passes through the third stage intercooler, giving up its heat of compression for that stage.

The air then enters the fourth stage cylinder through its suction valves on the downward stroke of the fourth stage piston. On the upward stroke of the fourth stage piston, the air is further compressed and discharged through the fourth stage discharge valves and against the pressure that happens to be in the bank being charged, thus building up the pressure in the bank to 3000 psi. This air passes through the aftercooler, the check valve, the separator, the charging stop valve, and up to the high-pressure receiving manifold.

Each compression stage is furnished with a safety valve, two thermometers, a pressure gage, a water separator, and a drain valve. The safety valves are set to blow when the internal pressure in the stage exceeds the allowable safe working pressure. The thermometers indicate the air temperature at the inlet and outlet port of each stage. The pressure gages, grouped together on the gage board, indicate the pressure condition within each compression cylinder. The drain valves are used to drain moisture from each stage cooler separator.

2C3. Lubrication. Lubrication is accomplished by two systems, the pressure system and the forced-feed lubricator. The forced-feed lubricator, controlled by four adjusting knobs, supplies oil to the piston rings, cylinders, and air valves. The pressure system is supplied with oil by a rotary oil pump actuated by the crankshaft. Oil circulates

 
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from the oil sump, through a Cuno oil filter to all bearing surfaces in the compressor. Oil for the pressure system is cooled by the oil cooler attached to the after end of the bed plate.

2C4. Cooling. As in the automobile engine, the pistons and cylinders of the compressor must be cooled to prevent damage by the heat developed by the compression of air. A water-circulating system is used for this purpose. Cooling water is supplied to the pipe header by means of a water pump attached to the left side of the center frame. From there, water is distributed through branch piping to the intercoolers, the aftercooler, the oil cooler, and the cylinder water jackets. Finally, it is discharged overboard.

The relief valves at the second and third intercoolers and at the aftercooler are set to open when the, water pressure in the system exceeds 150 psi. The cooling system requires approximately 35 gallons of water per minute at 70 degrees Fahrenheit.

2C5. Operating principles. Each

  compressor has a capacity of 20 cubic feet per hour at 3000 psi.

To start the compressor, the valves in the water cooling line, the discharge drain valve in the fourth stage, and all drain valves from the air piping of the compressor are opened. Then the motor is started by pressing the push-button controls, and the speed is regulated by adjusting the rheostat. After the normal speed has been reached, the first, second, third, and fourth stage drain valves are closed successively, allowing the pressure within the stages to be built up gradually. The oil pressure must also be up to the proper point before the machine is placed in service.

In securing the compressor, the current is turned off and all stage drain valves are opened. The pressure within the compressor is gradually reduced. The check valve at the aftercooler prevents the compressed air in the ship's banks from backing up.

The speed of the compressor should never exceed 550 rpm, because overspeeding may damage the moving parts and the valves.

Figure 2-5. Reducing valve and bypass to torpedo impulse charging manifold.
Figure 2-5. Reducing valve and bypass to torpedo impulse charging manifold.
 
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D. TORPEDO IMPULSE FLASKS
 
2D1. Description. The impulse flasks, forming part of the impulse air system mentioned in Section 2A4, are steel cylinders, dome-shaped at each end. One of the domed ends is flanged and is provided with a port which connects to the impulse lines. There is an impulse flask for each torpedo tube. The six flasks that are mounted in the superstructure above the forward torpedo room are approximately 5 feet 10 inches in length and 16 inches in diameter; the four flasks mounted below the after torpedo room deck are approximately 5 feet 3 inches, in length and 18 inches in diameter.

A torpedo impulse flask has a capacity of approximately 7 cubic feet. It stores air which is received through the charging line from

  the torpedo impulse charging manifold at a pressure of 600 psi. The air that is stored in the impulse flasks is used in firing the torpedoes from the torpedo tubes. A swing check valve prevents the air from being forced back to the manifold. Each impulse flask is connected to the corresponding torpedo firing valve by a line bypassing the swing check valve.

When the torpedo firing valve is opened, air from the impulse flask discharges into the breech of the torpedo tube, forcing the torpedo out of the tube.

The impulse flask, charging manifold, valves, and lines are tested hydrostatically to a pressure of 900 psi or 150 percent of the maximum working pressure.

 
E. BYPASS AND REDUCING VALVES FOR 600-POUND
TORPEDO TUBE IMPULSE AIR SYSTEM
 
2E1. Description. The reducing valves provide the torpedo tube impulse system with 600-pound air by reducing the 3000-pound pressure of the high-pressure air system to 600 pounds. In practice, the reducing valves may be set below 600 pounds for a lower impulse pressure.* Bypass lines with manually operated bypass valves are provided to supply high-pressure air directly from the 3000-pound service lines to the torpedo impulse system in the event of failure of a reducing valve, or in the event that an impulse pressure above the reducer setting is required.

One reducing valve is installed at the end of the forward 3000-pound air service line on the starboard side of the forward torpedo room, and another at the end of the after 3000-pound air service line in the after torpedo room. The bypass valve and line are located above the reducing valve in each case. (See Figure 2-5.) In the forward torpedo room, the reducing valve and the bypass valve and line supply two torpedo impulse flask charging manifolds. In the after torpedo room, they supply one manifold.

The reducing valves are of the balanced

*Pressures as low as 300 pounds at periscope depth are used.

  pressure type, set to receive air at a pressure of 3000 psi and to discharge it at a pressure of 600 pounds.

The mechanical construction of the valve is shown in Figure 2-6. A detailed description is given in Section 4C.

2E2. Operation. To supply air to the torpedo impulse air system, the stop valves on both sides of the reducing valve are opened. This allows air to enter the high-pressure side of the reducing valve. When the pressure in the torpedo impulse flask charging lines is less than 600 psi, the diaphragm in the reducing valve unseats the valve disk, permitting the high-pressure air to enter the lines. The entering air is instantly reduced to the required pressure by the valve action. It continues to flow until a pressure of 600 psi has been built up in the torpedo impulse flask charging lines. With the slightest drop in the pressure on the discharge side of the reducing valve, the pressure in the dome forces the valve open, allowing a controlled volume of air to pass, and thereby maintaining the delivery at a constant pressure of 600 pounds.

The bypass valve allows air to enter the torpedo impulse flask charging manifold

 
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Figure 2-6. Grove reducing valve.
Figure 2-6. Grove reducing valve.
 
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directly from the 3000-pound service line without passing through the reducing valve. The bypass valve should be opened slowly, allowing the high-pressure air to enter the lines   gradually. It should be shut as soon as the pressure gage registers 600 psi in the torpedo impulse air system.
 
F. TORPEDO IMPULSE CHARGING MANIFOLDS
 
2F1. Description. The torpedo impulse flask charging manifolds charge the torpedo impulse flasks described in Section 2D. There are three such manifolds aboard the vessel, two in the forward torpedo room each serving three flasks, and one in the after torpedo room serving four flasks.

Figure 2-3 is an illustration of the charging manifold in the after torpedo room. Its construction is typical of all three manifolds. It consists of a cast-bronze body, cylindrical in shape, with four valves and pipe connections leading to the four impulse flasks, a supply line connection, a pressure gage connection, and a relief valve connection. The relief valve, of the type described in Section 4I, is set to blow when the pressure in the manifold exceeds 675 psi. Each valve is

  operated by a handwheel, on the rim of which is stamped the function of the valve.

The two impulse flask charging manifolds in the forward torpedo room are of similar construction, except that each serves only three impulse flasks and therefore is provided with only three valves and pipe connections.

Air is supplied to the charging manifolds at 600 psi from the 3000-to-600-pound reducing valve described in Section 2E. To charge a flask, the reducing valve must be opened to permit air to enter the chamber of the manifold. When the manifold pressure registers 600 pounds, the valve directing the flow from the charging manifold to the selected impulse flask is opened. The flask is fully charged when its pressure gage reads 600 psi.

 
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