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Appendix B

Air Induction & Snorkel Induction Systems

Made available by Bob Emery of the Submariners Association of Canada West


While on the surface air is introduced into the submarine through the main induction valve, the largest valve on the submarine. The main induction is 36 inches in diameter and is located in the after part of the sail approx. 28 feet above the keel. It is of the poppet mushroom type with an umbrella type hood. Air entering through the valve must first pass under this hood, which helps reduce water or spray during heavier seas. The main induction valve operating mechanism is located in the forward end of the after battery compartment and is normally operated hydraulically from the hydraulic manifold in the control room.


Connected to the main induction are three air induction lines, along with a line to the snorkel induction system. The ship's ventilation line is 16 inches in diameter and runs aft to a point above the forward end of the forward engine room. Here it accesses the pressure hull via the ship's ventilation hull valve and into the ventilation supply system. Two larger induction lines, 22 inches in diameter, also run aft from the main induction. The port line accesses the pressure hull via the forward engine room induction hull valve and supplies the forward engines. The starboard line accesses the pressure hull via the after engine room induction hull valve and supplies the after engines. An inboard hood surrounds the engine induction hull openings, with a sheet metal piping leading to the lower flats to prevent water carry-overs to machinery and crew. All outboard induction lines, valves and fittings are designed for maximum submergence pressure. There are drain lines installed to indicate flooded piping and the induction piping will hold approx. 18 tons of seawater if flooded during a casualty. The three induction hull valves are of the flapper type and their operating gear consists of a lever with a quick release mechanism. They are manually operated by a hand lever with a cam locking device held open by a quick release locking device. When the quick release grip is depressed, the locking device is withdrawn and the valves seat with their own weight. A gagging screw is provided so the valves can be gagged shut internally for pressure tests or other damage control purposes.



The snorkel induction mast is made up of a vertical, fixed base pipe and a telescoping section. The telescoping section may be completely retracted into the base pipe or positioned above it at various predetermined operating positions. The telescoping section is raised and lowered by hydraulically driven gears and shafting. The exhaust mast and induction mast are geared together and are raised and lowered simultaneously. The fixed base pipe forms a watertight tube for an air intake between its uppermost extremity and the piping leading to the branch lines of the main induction valve.

When the telescoping section is in one of its operating positions, the watertight tube is extended to the height of the head valve. In the housed position, or any position other than an operating position, the mast will flood at the juncture of the two piping sections. Watertight seals are formed between the two sections of piping when the mast is in the operating positions. The seals consist of built up circular steel bands around the lower outer surface of the telescoping section and circular neoprene (rubber) insert gaskets that are imbedded in the inner surface of the fixed base pipe. The neoprene gaskets are installed at specified Intervals in the pipe to provide for multi height snorkel operation.

When the snorkel induction mast is flooded, it contains approximately 8,000 pounds of seawater. Prior to snorkelling, the water must be removed from the snorkel induction mast. The water is drained or blown to negative tank.

As noted above, the snorkel induction mast is constructed to permit snorkelling at various depths. It can be operated in conjunction with radar antennas and periscopes in such a way that all are exposed to the proper amount for maximum efficiency and minimum exposure.

Snorkelling can be conducted at either the No. 1 periscope depth or the search radar depth, with the actual snorkelling depth being usually controlled by the sea state.

When there is an increased risk of flooding through the main induction when surfaced during particularly heavy weather, the main induction valve can be shut and the snorkel induction mast utilized to introduce operating air into the submarine.


The snorkel head valve, together with its housing, is a unit capping the snorkel induction mast. The snorkel head valve is a 21" poppet type, quick shutting valve designed to minimize the amount of water taken into the induction system during snorkel operations. When snorkelling, the head valve housing is normally the only part of the submarine exposed above the water's surface, with the exception of antennas and masts which may be in use.

The head valve is automatically operated by an electro pneumatic control system, which is installed as a part of the head valve safety circuit. When the head valve electrodes, which are externally mounted on the head valve housing below the level of the valve seat, are above the water's surface, service air is admitted by the head valve control valve to hold the head valve open against spring pressure. If the electrodes are immersed, the head valve control valve vents off. the opening air and supplies service air to the other side of the power cylinder, causing the head valve to shut by air pressure, spring pressure, and the weight of the valve. Thus the head valve is opened by air pressure alone and shut by spring pressure, air pressure, and the weight of the valve.

The head valve control system is designed to 'fail safe'. The head valve will shut if air pressure and/or electric power fail.

An electro pneumatic control valve located in the control room controls the snorkel head valve. The control valve is normally operated automatically by a solenoid installed as a part of the head valve safety circuit. Installed on the control valve is a hand operated latch, which is used to hold the head valve open (if desired) while operating under normal surface conditions. The head valve may be held open during submerged operations if desired. An emergency shut control valve is also provided in the air supply system.


A water separator is installed in the snorkel induction piping between the snorkel induction mast and the snorkel induction valve. The water separator is cylindrical in shape. This water separator works on the principle that the inertia force of a column of air can be utilized to direct the air in a swirling motion inside the circular chamber.

When snorkelling, the engine scavenging air blower creates a vacuum in the ship, resulting in a constant intake of air through the snorkel induction mast and attached piping. The incoming air is passed through the water separator in a swirling motion. This action carries the heavier drops of water to the outer edge of the revolving air column where they are collected on a saw tooth edge baffle plate and allowed to run down the baffle plate into the drain provided in the base of the water separator.

Water collected there is drained to negative tank or to the pump room bilges (the water is usually drained to negative tank).


The air passes from the water separator through induction piping to the main induction stack. The snorkel induction valve is located in this line between the water separator and the trunk of the main induction valve.

The snorkel induction valve is approximately 15 inches in diameter, is of the flapper type and seats with air pressure. It is hydraulically operated from the snorkel control manifold located in the control room and may be manually operated from the crew's galley if hydraulic power is lost.



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Appendix AAppendix C