Patent ID: 7000895

Claim:
A valve assembly comprising: a housing having a valve chamber, a flow passageway extending through the valve chamber, and a piston chamber; a valve member in the housing and movable along a valve axis, the valve member including a plug portion arranged along the flow passageway for regulating fluid flow therethrough, the plug portion subjected to a first pressure urging the valve in a first direction; a piston slidable in the piston chamber integral with the valve member, the piston having a first side subjected to the first pressure urging the valve in a second direction opposite said first direction and a second side subjected to a second pressure urging the valve in the first direction; a pressure passage providing fluid pressure communication between the first side of the piston and the valve plug portion; and wherein the valve member includes a valve stem portion having a diameter that is smaller than a diameter of the plug portion, wherein a radially extending working face is formed between the stem portion and plug portion, and wherein the working face is subjected to said first pressure urging the valve in said second direction.