A Kingston valve is a type of valve fitted in the bottom of a ship's fuel, water and ballast tanks. Named after its inventor John Kingston (1786-1847), an English engineer.
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. The above describes certain ballast tanks, such as safety, negative and bow buoyancy tanks on vintage submarines. In general, main ballast tanks have the Kingston valve atop the tank. This Kingston valve, controllable both manually and hydraulically, is known by some as main vent operating gear. Main ballast tanks are in pairs; one on each side of the boat. One Kingston valve serves a pair, but each tank has a vent riser, with air connections and stop valves in the vent riser. The tank bottom is open to the sea through flood ports. The trapped air in the tank provides positive buoyancy while on the surface, although sea water sloshing in through the flood ports must be removed occasionally from the ballast tank(s) when cruising on the surface by means of low pressure air. The tank is capped by a vent riser, a pipe coming out of the top of the tank that terminates at a Kingston valve. In the vent riser is a valve that when shut, prevents flooding the tank when the submarine is rigged for surface. When the sub is rigged for dive, this valve is opened and flooding the tank becomes an option. Normally, the tank is flooded when the Kingston valve is opened, usually hydraulically from the control room. This Kingston valve then is left open until time to surface comes. This is because a slight leak of air from the air line provided to blow the tank into the vent riser could slowly make the boat more buoyant. When surfacing, the Kingston valve gets shut so the introduced air gets trapped in the tank and pushes the water out the tank's bottom through the flood port. The Kingston valve associated with each ballast tank can be operated manually. The vent riser valves get opened or shut manually during the rig for surface or rig for dive procedure.
Kingston valves are sometimes used to scuttle or sink a ship, as was done for example, to the German aircraft carrier Graf Zeppelin.