Fail-safe actuator device

摘要

The present invention relates to a fail-safe actuator of the type in which a piston riding in a cylinder is urged toward a port end of the cylinder by an energy storage spring. The piston is prevented from moving toward the port end so long as liquid remains entraped between the piston and port end, movement of the piston toward the port end resulting in shifting of a cable and consequent rotation of a quadrant about which the cable is arrayed to rotate a shaft. A rolling seal diaphragm is interposed between the piston and cylinder whereby leakage is prevented over protracted use periods, and the piston is isolated from liquid between the port and piston. Optionally, an annulus disposed between the piston and cylinder bears against the roll seal portion of the diaphragm preventing extrusion or permanent distortion of the diaphragm under high pressure conditions.