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INTRODUCTION
 
A. GENERAL
 
1A1. Importance of the air systems to submarines. The importance of the air systems to a submarine cannot be overemphasized since virtually every operation in the diving and surfacing procedure is dependent upon air provided by one or more of the air systems. Some of the more important operations depending on air pressure are the following:

a. The main hydraulic system operates because of the air pressure maintained in the air-accumulator flask.

b. Torpedoes are discharged from the submarine by air.

c. Tanks are blown by air.

d. The main propulsion engines are started by air.

Air, or more specifically compressed air, is necessary in order to surface, submerge, attack, and cruise. These functions, of course, are in addition to the use of compressed air and oxygen to revitalize the air in the ship after long periods of submergence. Pressure in the boat, a test for tightness, utilizes air.

The air systems represent, therefore, one of the most versatile of all systems aboard a submarine, in that they are capable of performing either as primary or secondary

  functions many of the operations performed in a submarine.

1A2. Basic principles of compressed air. The basis of the air systems is compressed air, which as the name implies, is air under pressure confined within the limits of a container. The force required for compression of the air is provided by the high-pressure air compressor, a simple machine which compresses air by means of a series of pistons, designed so that one or more pistons discharges air into another for further compression and finally through lines to banks for storage. Air can be compressed easily aboard a submarine, as it requires a relatively small plant and comparatively simple equipment. It can be stored at any convenient place and is always ready for use. Its action can be regulated to produce a low or high pressure, and yet it has enough elasticity or compressibility to cushion its impact against the equipment it operates. It consumes no valuable materials and can be supplied to any part of the submarine by simply extending a line from the air supply. Air, once stored, requires no further expenditure of energy for operation; but rather is a source of power for the operation of other equipment.

 
B. TYPES AND RELATIONSHIPS OF AIR SYSTEMS
 
1B1. General information. There are five separate air systems on the submarine: the 3000-pound high-pressure and torpedo impulse system, the 600-pound main ballast tank (MBT) blowing system, the 225-pound service air system (ship's service air), the 10-pound main ballast tank (MBT) blowing system and the salvage air system. (See Figure 1-1.)

The 600-pound MBT blowing system and the 225-pound service air system receive their supply of air from the 3000-pound air system. The 10-pound MBT blowing system is an independent system with its own

  low-pressure blower. The internal compartment salvage air system is dependent upon the 225-pound service air system, while the external compartment salvage air system is entirely dependent upon an outside source for its supply of air.

1B2. The 3000-pound and torpedo tube impulse air system. The 3000-pound air system consists of the 3000-pound high-pressure compressors, the high-pressure manifold, the interconnecting piping, valves, and compressed air banks. The main function of the 3000-pound air system is to compress, store, and supply air at the maximum pressure of 3000

 
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pounds per square inch for use within the 3000-pound, the 600-pound, and the 225-pound systems.

The 3000-pound air system also supplies air to the hydraulic accumulator air-loading manifold and to the forward and after 600 pound Grove reducing valves which supply the forward and after torpedo tube impulse-charging manifolds.

The 3000-pound air system is equipped with an external charging connection so that the system may be supplied with air from an outside source.

1B3. The 600-pound MBT blowing system. The function of the 600-pound MBT blowing manifold and system is to remove water ballast from the main ballast tanks, or the fuel ballast tanks when they are used as main ballast tanks, during surfacing of the submarine. It receives its supply of compressed air from the high-pressure system through the distributing manifold.

1B4. The 225-pound service air system. The 225-pound service air system or, as it is sometimes called, ship's service air, in

  addition to blowing the variable group of tanks, provides the compressed air for all the miscellaneous services aboard the submarine. The 225-pound system consists of the 225-pound service air manifold, interconnecting piping, and various valves.

1B5. The 10-pound MBT blowing system. When the submarine has surfaced, the 10-pound main ballast tank blowing system is used to conserve the compressed air stored in the ship's air banks. The system consists of its own low-pressure blower, control manifold, and piping to the various main ballast tanks. The 10-pound system is operated only after the submarine has surfaced sufficiently to permit the opening of induction valves and hatches.

1B6. The salvage air system. This system actually consists of three separate systems the MBT external salvage, compartment external salvage, and compartment internal salvage. The external salvage connections permit compressed air from an outside source to be supplied to the tanks and/or compartments, while the internal salvage system utilizes the ship's air for compartment salvage only.

 
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Figure 1-1. COMPREHENSIVE SCHEMATIC OF AIR SYSTEMS.

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