A pneumatic actuator uses compressed air against a piston to drive the valve. Where an instrument air supply already exists on the plant floor, it is typically the lower-cost, faster-cycling and simpler option to install and maintain - and, fitted with a spring-return, it fails to a defined safe position automatically on loss of air with no battery or backup power needed.
An electric actuator uses a motor and gearbox instead of air. It runs anywhere power is available, needs no compressor or air line run to the valve, and holds an intermediate position without the positioner and continuous air bleed a pneumatic control valve needs. It typically cycles slower than a pneumatic actuator of comparable size.
At a glance
| Pneumatic | Electric | |
|---|---|---|
| Needs on site | Compressed air supply (instrument air) | Electrical power only |
| Cycle speed | Fast - typically under a few seconds | Slower - typically tens of seconds |
| Fail-safe on loss of supply | Spring-return fails to a defined position automatically, no backup power needed | Needs a battery or capacitor backup to fail safely - not automatic by default |
| Position holding | Needs a positioner and continuous air bleed for modulating control | Holds position natively once the motor stops - no continuous supply needed |
| Where it suits best | Plant with existing instrument air, high-cycle or fast-response duty | Remote or unmanned sites, precise modulating control, no air infrastructure |
Frequently asked
Which one is more expensive?
It depends on what already exists on site. If instrument air is already run to the valve location, a pneumatic actuator is usually the lower installed cost. If there is no air infrastructure and running a line would mean a new compressor or a long air-line run, an electric actuator can work out cheaper overall despite a higher unit cost.
Can an electric actuator fail safely like a spring-return pneumatic one?
Only with an added battery or capacitor backup module to drive it to the fail position on power loss - it is not automatic the way a pneumatic spring-return actuator is. Confirm this is fitted if fail-safe behaviour is a requirement for the duty.
Is one faster than the other?
Pneumatic actuators generally cycle faster for a given size, which is why they are the default for high-cycle switching duty. Electric actuators are usually chosen for their precision and independence from an air supply rather than for speed.
Related
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