Control valve system for blowout preventers

For use with a blowout preventer having an actuating cylinder and piston for actuating the closing of the blowout preventer, the actuating piston having a closing side and an opening side of smaller effective area than the closing side, a differential pressure control valve system comprising:

• a directional flow control system for directing flow from the opening side of the actuating piston alternatively to the closing side of the actuating piston and to a discharge point;
• and
• a pressure sensitive switching system in communication with the directional flow control system, said switching system being operative, upon the communication of a pressurized fluid to the closing side of said actuating piston, to cause said directional flow control system to direct flow from the opening side of the actuating piston to the closing side of the actuating piston when the pressure at the closing side of the actuating piston is below a predetermined magnitude, and to automatically vary the alternative flow paths of the directional flow control system when the pressure at the closing side of the actuating piston reaches said predetermined magnitude to cause said directional flow control system to direct flow from the opening side of the actuating piston to said discharge point;
• said pressure sensitive switching system further comprising an override system for selectively causing said directional flow control system to direct flow from the opening side of the actuating piston to the discharge point independently of the pressure at the closing side of the actuating piston.