How to select the type of pneumatic actuator with single action?

The pneumatic actuator has two operating modes: single acting and double acting.

The valve controlled by the double acting pneumatic actuator completely relies on compressed air to produce thrust on the cylinder piston from different directions, driving the spool to rotate axially, and realizing the opening and closing of the valve. Close.

Single acting pneumatic valves, although also need to rely on compressed air to open or close the valve, but because the actuator is equipped with a spring return device. Therefore, when the pneumatic valve loses sustained supply pressure, the valve will automatically return to the initial state of the valve under the reaction force of the spring.

Because of the different working conditions and environment, single acting pneumatic valves are divided into normally open type and normally closed type. Normally open type refers to the pneumatic valve when the original state of the valve is set to open state. Therefore, in the piping system, when the valve needs to be closed, just keep filling the right amount of air into the pneumatic valve actuator. High pressure compressed air can close the valve. If you need to open the valve again, just stop charging the actuator of the pneumatic valve. Due to the loss of sustained air pressure, the valve automatically returns to its original state under the action of elastic potential energy of the spring. Similarly, the normally closed type pneumatic valve works in the same way as the normally open type, but the original state of the valve is set differently when it leaves the factory.

On the selection of single acting pneumatic actuator:

Single acting actuator is the operating mechanism of pneumatic valve. In spring return applications, the output torque is obtained during two different operations. Each operation produces two different torque values depending on the stroke position (0° and 90°). The torque arm is multiplied by the force (air or spring-applied stopper) to obtain the output torque of the spring return actuator.

The first case is the pressure into the compression spring after the output torque, known as "pneumatic stroke output torque". In this case, the air source pressure is forced from 0° to the 90° position, resulting in a reaction force due to the compression of the spring. , the torque gradually decreases from the maximum value of the starting position to 90°.

The second case is that the output torque is obtained by the spring restoring force acting on the piston when the gas is lost, which is called "spring stroke output torque". In this case, the output torque decreases gradually from 90° to 0° due to the extension of the spring.

To sum up: the single acting pneumatic actuator is designed on the basis of producing balance torque under two conditions. That is, the number of springs per side is the same as the air source pressure value (4bar-4 springs per side).

In each case, it is possible to obtain an unbalanced moment. By changing the relationship between the number of springs on each side and the air source pressure.

Two conditions are available in spring return applications: open failure or close failure. Under normal working conditions, the recommended safety factor of spring return actuator mechanism is 20~25%.