Actuator with locking valves

Abstract

A hydraulic actuator having two balanced area actuator pistons, each controlled by the movement of a primary servo sleeve to supply pressurized fluid from a pressure fluid source to one side of the actuator piston and to allow return flow from the opposite side of the piston. Piston movement is reversed by translation of the primary servo sleeve. A blocking valve is in each flow line between the servo sleeve and the cylinders in which each piston moves. A flow channel from the pressure fluid source applies pressure to the shut off valves to maintain the valves normally open for flow of control fluid to and from the actuator pistons. Means, operable upon loss of fluid pressure, are provided for closing the shut off valves to maintain existing pressure on both sides of the actuator pistons automatically to maintain reactive loads in each actuator half. Upon pressure loss, disengagement of the shut off valves may be accomplished by stroking a secondary spool associated with the primary servo spool and responsive to over travel of the primary servo spool to displace a ball which in turn mechanically displaces the shut off valves to allow passage of fluid to and from the actuator cavities thereby permitting an equalization of pressure on both sides of the actuator piston.

Dependencies are inferred from the claim text.