Lift check valve with dashpot

An improved check valve of the type having a valve body with a passage therethrough intersected by an operating chamber terminating at the passage with a valve seat and a disc movable in the chamber toward a closed position engaging the valve seat by fluid flow forces in one direction and an open position spaced therefrom by fluid flow forces in the other direction, the improvement comprising:

• a cylindrical member connected at one end to the disc and at the other end to a piston having a peripheral surface adjacent the interior surface of the operating chamber and defining thereabove an upper chamber;
• a baffle plate in the operating chamber axially between said piston and said disc and surrounding said cylindrical member at an axial opening whereby said piston, said baffle means, said interior surface and cylindrical member define therebetween a dashpot chamber having a predetermined volume of liquid therein in the open position;
• means for limiting the rate at which liquid leaves the dashpot chamber as the disc moves from said open position to the closed position and thereby the closing rate of said disc;
• and conduit means fluidly communicating the upper chamber with the passage at a location upstream of the valve seat when the flow is in said one direction, said conduit means establishing a pressure balance between the upper chamber and said location providing an upward biasing on the piston for flow in said other direction and preventing fluid conditions in the upper chamber from retarding the closing rate for flow in said one direction whereby the closing rate is prescribed by the rate at which the liquid leaves the dashpot chamber.