Sizing a pneumatic actuator to a valve comes down to four inputs: the valve's required operating torque, the air pressure actually available at the actuator, the fail-safe behaviour needed, and how often the valve cycles.
The sizing process
Get the valve's torque requirement
The valve manufacturer specifies break-to-open, running and end-of-travel torque figures - usually in Nm. Use the highest of these (typically break-to-open) as your baseline.
Confirm the actual available air pressure
Don't assume the nameplate rating - measure or confirm the pressure actually reaching the actuator at the installation point, since line losses reduce it below the compressor's output.
Apply a safety margin
A safety factor of roughly 1.25–1.5× the valve's required torque is standard practice, to cover friction increase over time, seat wear and any spec uncertainty.
Decide fail-safe behaviour
If the application needs a defined position on air loss, choose single-acting (spring-return) and confirm the actuator's spring-end torque still clears the valve requirement at the worst-case (lowest) pressure. If not, double-acting is usually more economical.
Check duty cycle and life rating
High-frequency cycling applications (e.g. curing presses) need an actuator rated for the expected cycle count - ask for the manufacturer's rated cycle life, not just the torque curve.
Work out the figure to specify
Required actuator torque = valve break torque x safety factor. A factor of 1.25 to 1.5 is normal practice, covering friction increase over time, seat wear and spec uncertainty. The actuator must deliver that figure at your available supply pressure, not at its headline rating. The Duncan double-acting range runs DA 40 to DA 300, with the largest rated up to 1900 Nm at 8 bar.
Frequently asked
What torque unit do actuator and valve manufacturers use?
Nm (Newton-metres) is standard internationally; some older or US-sourced documentation uses lb-in or lb-ft - convert carefully, as a unit mismatch is a common sizing error.
Can you size an actuator for me?
Yes - send the valve's torque data (or the valve make/model/size) plus your available air pressure and fail-safe requirement, and we'll confirm the correct actuator size.
Related
Have valve torque data to size against?
Send it over and we'll confirm the right actuator.