Automatic bleed valves

Abstract

An automatic bleed valve bleeds gas from a liquid reservoir. It comprises a housing having a passage extending between an inlet and an outlet with the passage including a bore in which a piston is slidably received. The piston includes a capillary providing fluid communication between the inlet and a chamber formed in the passage adjacent the outlet. The piston is biased into an upstream position in which gas entering the inlet passes through the capillary to the chamber and thence to the outlet. However, the passage of liquid through the capillary so increases the pressure drop across the piston as to move the piston to a downstream position in which the piston closes the outlet to prevent communication between the chamber and the outlet, thus closing the valve. A downstream end of the piston is located in the chamber and has a greater area than the upstream end of the piston so that when the piston is in the downstream position the pressure of liquid in the chamber acting on the greater area maintains the valve closed, thus allowing the valve to accommodate pressure fluctuations in the reservoir. By a suitable reversal of parts, the valve can be used to bleed liquid from a pressurized gas reservoir.