Null-balance regulator valve

Claim 1

A null-balance valve for regulation of fluid flow comprising: a valve body having a fluid passageway therethrough; a plate slidably received in said valve body, the plate having an opening therein whereby in the opened position the opening is aligned with the fluid passageway in the valve body permitting fluid flow therethrough and in the closed position the closure plate blocks fluid flow through the valve body; a cylinder supported to the valve body and having a first fluid port adjacent one end thereof and a secon fluid port adjacent the other end thereof; a rolling diaphragm piston in said cylinder intermediate said ports, the piston being attached to said plate for positioning the plate, the force applied by said piston to the movement of said plate being equal to the difference in pressure at said first and second ports times the working area of said piston; and constant tension means normally urging said plate towards said opened or closed position, the direction of movement of the plate being determined by the force applied by said constant tension means versus the force applied by said piston, the force required to move said plate towards said opened or closed position as applied by said piston being substantially constant at all positions of said plate.