Pneumatic double-acting actuators use gas (typically air or nitrogen) to pressurise a double-acting cylinder. When activated, the pressurised gas causes an imbalance in the opposing cylinder areas and drives the connected shaft in the required direction. A 4-way solenoid valve is used to switch pressure between the cylinders.
The normal position is that in which the solenoid is de-energised. Available output force is equal to the pressure times the area of the piston (F=PxA). Piston actuators are typically sized for 80psi minimum. Double acting actuators do not have an inherent fail safe action. If only electrical power is lost, and the friction in the valve and actuator is sufficient to overcome the dynamic unbalance in the valve, then the valve will remain in its last position. If the dynamic unbalance force is greater, the the valve will drift in the dominating direction.
Please note: This is for information only; Zetco Valves no longer offers actuated valves.