Pneumatic actuators: Simple effect and double effect: Which one should I choose?

DIFFERENCES BETWEEN SINGLE AND DOUBLE ACTING
A pneumatic actuator is a device that transforms the energy of compressed air into mechanical energy, this characteristic allows it to open or close valves control in piping systems.

In industrial applications of isolation or throttling valves, there are two different designs of actuator, if we understand the nature of its operation we will be able to determine which will be the best option for our installation:

In the case of the single acting actuator, it is characterized by being actuated by air on one side while on the other side it moves with help of a spring or membrane. Therefore, only one side of the actuator needs to be pressurized.

The double-acting actuator only uses one piston as an element to operate the valve, therefore, the actuator must be pressurized alternately from both sides.

Next, you can see the differences between both actuators in the following drawing:

WHICH IS THE BEST OPTION?
Depending on its design, a single or double acting actuator may be more optimal with respect to the requirements of the application, let’s see several cases:

Oil platform

PUSH OR TORQUE
Typically, in offshore oil and gas applications, the thrust or torque force of an actuator is achievable by both actuator models so it is not usually relevant. However, most manufacturers consider that double-acting actuators are more powerful, but they would only be necessary in applications where that extremely high torque is required.

SECURITY
In safety system applications with shut-off valves and purge valves, which require that the circuit closes when the signal or supply is lost, we will choose the single-acting actuator since the action of the spring will ensure that the valves remain closed. Double-acting actuators can also be used in safety systems, but their configuration would be more complex and expensive.

Estación de bombeo de agua

FAILED IN LAST POSITION
When it comes to regulation systems with throttling valves, the favorite actuator would be the double-acting one, since, if the signal or supply is lost, the failure position of the throttling valve would still maintain the latest production rate. In other words, in the event that it is required to fail the last position, the best option is the double-acting actuator.

Chemical plant

CONTROL APPLICATION
In the process control application that uses the control valve as its final element, the typical actuator is the single-acting one for 8-inch valves, while the larger valves 10-inch are usually actuated with double-acting actuators due to the high thrust required.

In applications with valves smaller than 10 inches, the double-acting actuator can also be used if there is a high torque required, in addition this actuator is more stable which offers more reliability in systems with sudden condition changes.