Kingston valve

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A Kingston valve is a type of valve fitted in the bottom of a ship's fuel, water and ballast tanks.

The valve connects the tank to the sea and when open, allows sea water to enter the tank for the purposes of cleaning the tanks and to admit water ballast.

On submarines Kingston valves are fitted at the bottom of the submarine's ballast tanks in order to admit water when the submarine dives. The valves allow water to enter the ballast tanks, the enclosed air escaping through the open main vents at the top of the ballast tanks. During peacetime the Kingston valves are closed when the submarine is on the surface, the valves and vents being opened to dive, but to reduce the time required for diving in wartime the Kingston valves are left permanently open when at sea, the water being kept out of the ballast tanks by the air pressure of the trapped air. This pressure is released when the vents are opened for diving, allowing the water to enter through the open Kingston valves.