Abstract: An automatic check valve, particularly adapted for use in installations where it is desired to have the valve close automatically when a rupture occurs on the supply side of a high-pressure pipe system. The valve element for the check valve, which is adapted to move toward or away from an annular valve seat formed in a valve body between inlet and outlet ports, has a cone portion, preferably a truncated cone portion, which extends through the opening formed by the valve seat in the valve cody. This truncated cone portion, which reduces the cross-sectional area presented to fluid flow through the valve as it closes upon the occurrence of a rupture, results in a damping action which prevents shocks to the piping system as the valve closes upon the occurrence of a rupture. An additional damping piston is connected to the valve element to assist in the damping action as the valve closes.