Patent ID: 8231102

Claim:
A flow-control valve comprising: a housing forming a flow passage having an intake port and an outlet port and a valve seat between the ports and having a lateral hollow part; an upstream valve body engageable with the seat and forming an upstream restriction; a downstream valve body forming a downstream restriction downstream of the upstream restriction; an control piston in the part defining therein an outer control compartment and an inner control compartment between the outer control compartment and the seat, the control piston being coupled to the downstream valve body for joint movement therewith; a high-pressure conduit connecting the outer control compartment to the flow passage upstream of the upstream restriction; a low-pressure conduit connecting the inner control compartment to the flow passage between the upstream and downstream restrictions; a connector element connected to the upstream valve body, extending through the control piston, and having an outer end projecting out of the housing; and pressure-relief means between the control piston and the outer end for exerting on the connector element a force urging the upstream valve body upstream and generally equal to a pressure differential across the upstream restriction.