Actuators

Driving valves pneumatically or electrically?

In today’s process industry, less and less is done manually. Valves and taps are often opened and closed with mechanical support. The choice between pneumatic or electric actuator depends on several factors. The simplest criterion is the availability of electricity and/or compressed air. But there are other considerations, related to safety and process control.

Pneumatic actuator: open or closed

If a valve only needs to be opened or closed, a pneumatic actuator is a great option. The main advantage of this option is its speed. When controlled by air pressure, the valve opens or closes within a maximum of two seconds. Although it could be done with some skill, with you wouldn’t normally choose to open a tap only partially using a pneumatic actuator – it needs to be either open or closed. There are two different types of pneumatic actuators.

Single-acting pneumatic actuator

A single-acting drive works using air pressure in one direction. By increasing the pressure, the walls of a pressure chamber are pushed apart. The movement is linked to a gear that drives the shaft of the valve and opens it. Powerful springs are mounted behind the walls of the pressure chamber, and these compress the chamber again when air pressure drops. As a result, the valve closes immediately. The advantage of a single-acting pneumatic actuator is that in the event of a loss of pressure – e.g., in the event of a short circuit or other defect – the valve automatically returns to its safe basic position thanks to the springs.

Double-acting pneumatic actuator

The double-acting actuator works according to the same operating principle, with the significant difference that there are no springs to provide return pressure – opening and closing is done by reversing air pressure. If the air pressure is lost, the valve remains in its current position. This can be less safe if, in the event of a pressure failure later in the process, a defect occurs which forces the flow of the medium to stop.

Electrical actuator

A valve actuator with an electric motor has the advantage that the actuator can gradually close the valve or tap to reduce the flow without shutting it off completely. Depending on the valve and actuator, it can take up to two minutes to close the valve completely. In emergencies, this may not be fast enough. The advantage of closing evenly is that there is no pressure wave: the so-called ‘recoil’. If a ball valve or butterfly valve is close to a bend, operating the valve too quickly can cause a shock and damage the pipework.

FailSafe actuators – smart actuators

Electrical actuators do come with a risk: in the event of a power failure, the valve remains in its last position, whereas single-acting pneumatic actuators automatically push the valve back into a safe position in the event of pressure loss. Our suppliers have a solution for this: the Failsafe actuator. These Fail-Safe actuators are equipped with powerful springs, like the pneumatic version, or with a backup source for electricity. In other words, a battery or supercapacitor with sufficient power to return the drive to its safe basic position even after the mains power fails. Our suppliers Valpes and PS Automation also offer ‘smart drives’ that you can set up with an app and Bluetooth from your smartphone or from the machine room.

Positioner passes on positioning

Modern actuators can also be equipped with an integrated positioner that remotely indicates the position of the tap. This allows you to remotely control all automated valves in the entire process plant, for even better process management.

Limit switches

In the case of pneumatic actuators, it is possible to add a limit switch that uses a remote electrical signal to indicate whether the valve is open or closed.

Which electric or pneumatic actuator is most suitable?

Each process is different, every application requires tailor-made solutions. If you already know exactly what you need, you can order the right drive directly in our web shop. Would you like advice or a second opinion from a specialist? Don’t hesitate to get in touch!