US Patent 7921876 Rotary control valve and associated actuator control system

A rotary control valve and associated actuator control system. An actuator control system comprises a rotary control valve including a generally planar face seal, and an actuator operatively connected to the rotary control valve. Another actuator control system comprises a control valve including multiple faces having multiple ports formed therein. Fluid communication is selectively permitted and prevented between the ports in response to relative displacement between the faces. A differential area is configured to apply a biasing force which maintains sealing engagement between the faces, and which increases in response to an increase in pressure applied to the control valve.