Combination pressure-vacuum relief and antipollution valve

Abstract

A combination venting and antipollution device for a shipboard liquid storage tank. A closure wall divides the vent conduit into a lower tank chamber in direct communication with the tank and an upper vent space in direct communication with the vent opening. A spring-urged valve closure member opens or closes an opening through the closure wall. Low pressure in the tank moves the valve closure member down into a lower open position, to admit air or other fluid to the tank; high pressure in the tank moves the valve closure member up into an upper open position to vent air from the tank. A hydrostatic pressure chamber open to the atmosphere houses a sealed bellows, and a spill-lock valve secured to the bellows normally opens to the vent a spill-lock chamber on the vent side of the valve closure member. However, when the pressure in the pressure chamber (or manual action) compresses the bellows (as when the ship sinks), the bellows moves the spill-lock valve to close the connection to the vent and cause the fluid from the tank chamber to flow into the spill-lock chamber, to bear upon a spill-lock piston there. In this condition, the tank pressure acts on the spill-lock piston to prevent the valve closure member from moving up into its upper position until the pressure in the tank chamber is well above that then present in the vent space, but the tank pressure does not restrain the valve closure member from moving down into its lower open position. Salvage operation is also provided for.