Patent ID: 7520291

Claim:
A gate valve comprising: a body having an axial passage and a lateral passage intersecting the axial passage, the outer ends of the axial and lateral passages providing an inlet and outlet respectively, the inner end of the lateral passage providing a valve seat; a valve actuator axially movable in the axial passage between a valve closed position blocking flow through the lateral passage and a valve open position in which fluid flow through the lateral passage is possible; the valve actuator including a transverse blind hole open on a side adjacent the lateral passage, a gate transversly movable and at least partially within the blind hole and adapted to block the lateral passage in the valve closed position and a pressure spring in the blind hole urging the gate against the valve seat; the valve actuator further including an axial stem extending from the axial passage on the end opposite the valve inlet; and, a pressure compensator responsive to ambient pressure which applies a force to the stem in a direction that tends to move the valve actuator to the valve closed position such that an increase in ambient pressure results in a greater applied force to the stem, the pressure compensator comprising a first fluid-filled chamber said first fluid-filled chamber having an opening which slidably engages the stem of the valve actuator in a fluid-tight relation; a second chamber open to the ambient environment; a free piston slidably disposed within a cylinder, the cylinder being open on a first end to the first chamber and open on a second end to the second chamber such that an increase in ambient pressure effects an increase in the fluid pressure of the first fluid-filled chamber and movement of the valve actuator to the valve open position causes a movement of the piston which effects a decrease in the volume of the second chamber.