Pilot operated check valve

A pilot operated check valve comprising a poppet valve movable into engagement with a valve seat defined by a partition wall between a primary-side fluid compartment and a secondary-side fluid compartment by action of hydraulic pressure on the secondary side and adapted to close on the secondary side, a fluid passageway extending through the partition wall, means for actuating the poppet valve so as to move it out of engagement with the valve seat against hydraulic pressure on the secondary side, said poppet valve having a spool member integrally therewith on a front side thereof and adapted to slidably and closely fit into said fluid passageway, and O-ring mounting groove provided on said spool member in abutment relation with a seating surface of said poppet valve opposed to said valve seat so that an O-ring may be positioned in said fluid passageway upon said seating surface being brought into engagement with said valve seat, said O-ring mounted in said groove, a passage for fluid flow in said spool member leading from the front end of said spool member facing the primary-side fluid compartment to the secondary-side end surface of said spool member adjacent said O-ring mounting groove, at least a portion of said O-ring mounting groove communicating with said secondary-side fluid compartment through a restricted fluid passage.