Gas-hydraulic pressure type actuator for pipeline valve

Abstract From the Canadian patent

An actuator for a valve disposed in a gas pipe line is driven directly by the gas pressure in the pipe line which is tapped off and supplied to the appropriate end of the actuator cylinder via an electromagnetic spool valve. A hydraulic transfer circuit couples the chambers on the piston rod sides of the actuator cylinder, and includes flow control valves for regulating the actuator speed and an oil expansion tank. The latter may be sealed and a positive pressure established therein to facilitate the oil transfer. A hand pump may also be provided to implement the oil transfer and drive the actuator piston from the piston rod side if the gas pressure is too low to power the actuator.