Relieving valve with surge control for fluid storage tank

Abstract From the Canadian patent

A relieving valve for a fluid or liquid storage tank to permit release of pressure from inside the tank as necessary. A piston is movable within the valve to open the same to atmosphere as pressure builds up slowly therewithin. Upon occurrence of a sudden or rapid pressure rise in the tank such as when the, fluid therein surges against the valve a snubber assembly in, the valve is moved by said pressure rise to a partially closed position to impede the rate at which pressure can build within the valve and thus increase the time before which the valve opens to atmosphere.