Solenoid valves are used to operate pneumatic actuators, acting upon electrical signals to admit and exhaust supply pressure to the actuator. Three-way solenoid valves are generally used with spring return actuators, and four-way solenoids on double acting actuators. Solenoid valves manufactured by ASCO (Automatic Switch Co.) are regularly furnished with pneumatic actuators when ordered with solenoid valves. When solenoid valves are ordered with actuators, they are assembled to the actuator and tested before shipment from the factory. Solenoid Valves on Double Acting Actuators. Solenoid valves are normally mounted on double acting actuators to provide for ball valve closure on loss of electrical power. If valve opening is required, the solenoid valve will be mounted with the connections reversed. Valves with double acting actuators will remain in place on loss of supply air pressure. Solenoid Valves on Spring Return Actuators. Solenoid valves are normally mounted on spring return actuators to provide for ball valve closure on loss of electrical power or supply air. If valve opening is required, the solenoid valve will be mounted with the connections the same, but the actuator will be mounted on the valve with the valve in the open position. This means that the valve will rotate clock-wise to open, counterclockwise to close, opposite the normal convention. The pistons in the actuator must be reversed at extra cost to convert the actuator to reverse rotation for the valve to rotate counter-clockwise to fail open. Reverse rotating actuators are required for control valves and certain multi-port valve configurations to function properly.