A housing has a pilot bore with an electrically controlled pilot valve therein, an intermediate bore with an intermediate valve therein, and an engine bore with a main valve therein, each valve being reciprocable between first and second stable positions. When said pilot valve is switched to its first stable position, high pressure hydraulic fluid drives said intermediate valve to its first stable position and releases said engine valve from its second stable position, whereupon a double acting spring drives the engine valve toward its first stable position. High pressure hydraulic fluid completes this movement then holds the main valve in its first stable position against the force of the double acting spring. Switching the pilot valve to its second stable position effects movement of the other valves back to their second stable positions.