Yield valve

摘要

A yield valve comprises a valve body, a first inlet port, an outlet port, a valve seat, and a valve member movable between a first position in which it cooperates with the valve seat to prevent fluid communication between the inlet port and the outlet port and a second position in which the outlet port is brought into fluid communication with the inlet port. One side of the valve member is subjected to the pressure of fluid at the inlet port to urge the valve member towards its second position. Spring means acts on the other side of the valve member to urge the valve member towards its first position. The valve also has a valve chamber isolated from the inlet port and from the outlet port and a second inlet port for supplying a fluid under pressure to the chamber. The valve chamber is so arranged with respect to the valve member and the spring means that fluid pressure within the chamber will act on the valve member to urge the valve member towards its first position and will act on the spring means so as to reduce the force applied to the valve member by the spring means by an amount at least substantially equal to the force applied by the fluid pressure to the valve member.