Differential-pressure valve

A differential-line pressure valve including a valve passageway formed through a fixed wall and closable by a valve member displaceable by a differential-line pressure sensor biased to close the valve passageway and having its opposite faces subjected to the differential-line pressure such that the higher pressure applied to one face of the sensor tends to open the valve passageway and the lower pressure applied to the opposite face of the sensor tends to close the valve passageway, characterized in that the high-pressure face of the sensor has fixed thereto the valve member movable to open and close said passageway, and also has fixed thereto an annular sealing surface circumscribing the valve member, such that when the sensor is in its valve-closed position, the annular sealing surface seals off the portion of the high-pressure face of the sensor circumscribing said valve member from the high-pressure thereby increasing the differential-line pressure required to actuate the sensor to open the valve passageway, and when the sensor is in its valve-open position the annular sealing surface exposes said portion of the high-pressure face of the sensor to the high-pressure thereby decreasing the differential-line pressure required to actuate the sensor to close the valve passageway.