Double acting actuator：Control valve opening and closing.
Single acting actuator (Spring return)：When air or power is cut-off or
Broken, the actuator will close or open the valve automatically.
Double control solenoid valve：When a coil is energized, the valve Opens and the other coil turns off the valve when power is applied.With memory function (can be used for explosion一proof)
Limit switch (return device)：long-distance transmit signal when valve is open or closed (for explosion-proof type)