Press driven tool actuator module

摘要

A hydraulic actuator for a hydraulically driven device has a hydraulic cylinder, a first piston slidably received for reciprocation within the cylinder and defining a hydraulic fluid chamber with the cylinder, a second piston slidably received for reciprocation within a cavity in an actuator rod connected to the first piston and defining a gas chamber on one side of the second piston and an accumulator chamber on the other side of the second piston. A passage formed in the first piston communicates the hydraulic chamber with the accumulator chamber and a pressure relief valve selectively permits hydraulic fluid flow through the passage from the hydraulic chamber to the accumulator chamber to limit the maximum pressure of the hydraulic fluid within the hydraulic chamber and the hydraulically driven device. Preferably, during normal operation of the actuator and the hydraulically driven device the pressure of the hydraulic fluid is less than that required to open the pressure relief valve. The pressure of the gas in the gas chamber and acting on the second piston forces hydraulic fluid in the accumulator chamber into the hydraulic fluid chamber through a check valve when the pressure in the accumulator chamber is greater than the pressure in the hydraulic fluid chamber to reset the accumulator.