Fail-safe fluid piloted valve positioner with hydromechanical position lock

摘要

A fail-safe system for use on a hydraulic piloted pressure reducing and regulating valve for holding the valve at the last selected operating pressure in the event of loss of control signals. A pressure regulating valve having a body and a control piston therein is provided with a pilot piston in the body which is adapted to be connected to and responsive to a hydraulic signal pilot pressure. A segmented locking ring surrounds the assembly and coacting concentric V-shaped locking grooves are provided between the locking ring and the assembly for locking the assembly. The segmented ring is biased towards an unlocked position. An annular cam ring engages the exterior of the locking ring. Coacting wedge surfaces between the cam ring and the locking ring are provided for locking and releasing the locking ring. The cam ring is biased for urging the coacting wedge surfaces into engagement. A release piston engages the cam ring for moving the cam ring in a direction to disengage the coacting wedge surfaces upon the application of release pressure.