Fluid actuating device for an electric circuit breaker

A fluid actuating device for an electric switching apparatus such as a high-voltage power circuit breaker or the like includes an actuator for actuating the switching apparatus. The actuator in turn is made up of a cylinder and an actuator differential piston movable in the cylinder between positions corresponding to the open and closed positions of the switching apparatus. A fluid supply provides fluid under high-pressure to the end-faces of the actuator differential piston. A main-valve arrangement includes a main-valve differential piston movable for alternately interrupting and connecting fluid from the fluid supply to one of the end-faces of the actuator differential piston whereby the actuator differential piston is caused to move between its end positions. The main-valve differential piston also has end-faces fluidly connected to the fluid supply. A control valve arrangement includes a control differential piston which interrupts and connects the fluid supplied to one of the end-faces of the main-valve differential piston thereby actuating the same. A control arrangement actuates the control differential piston in response to inputs for opening and closing the switching apparatus. The main-valve differential piston and the control differential piston are actuable exclusively by the pressure of the fluid from the fluid supply and this enables the two last-mentioned pistons to maintain their end positions independent of the instantaneous value of the pressure of the fluid.