Flow control device

Claim 1

A flow control device comprising a housing having fluid inlet and fluid outlet passages therein, a first valve element disposed within said housing, a second valve element disposed within said first valve element, said first and second valve elements being disposed in selective communication with said inlet and outlet passages, said flow control device being characterized by: said first valve element comprising a metering element having inlet and outlet windows therein corresponding to, and communicating with said fluid inlet and outlet passages, respectively, said metering valve element being selectively positionable within said housing such that one of said windows is disposed in selectively variable registry with the corresponding passage for adjusting the effective flow area therebetween; said second valve element comprising a pressure regulating element having first and second ends thereof and including a first portion in variable registry with the other of said windows in said metering element for adjusting the flow therethrough; means providing fluid communication between said corresponding passage and said second end of said pressure regulating element; means providing fluid communication between said one window on a side thereof opposite said corresponding passage and said first end of said pressure regulating element; and means for balancing said pressure regulating element against fluid pressure on said first and second ends thereof for establishing a registry between said other window and said first portion of said pressure regulating valve element necessary to maintain a relatively constant pressure drop across said one window.