An actuator that is undersized cannot move the valve; one that is oversized wastes money and can damage the valve. Actuator sizing is not a guess — it is a calculation based on the torque the valve needs at its hardest condition, plus a safety margin for real-world variation. This guide covers the essentials so you can specify actuated valves with confidence.
Why Actuator Sizing Matters
Valves need different amounts of force at different moments. Breaking the disc or ball away from the seat takes the highest torque; running torque and seating torque are lower. If the actuator is sized on average torque instead of breakaway torque, it will stall. If it is oversized, you pay for a bigger cylinder, motor and price, and the extra force can damage seats and stems.
Calculate the Required Torque
The total torque the actuator must deliver is the sum of:
- Valve breakaway torque — from the manufacturer data sheet, at the maximum differential pressure across the valve
- Packing and stem friction — increases with packing type and temperature
- Media effects — sticky, viscous or solids-laden media raise friction
Ask the valve manufacturer for the torque table, not a single number: torque changes with pressure, direction and temperature, and the worst case — usually the highest differential pressure — is what sizes the actuator.
Apply a Safety Factor
Once you have the required torque, multiply by a safety factor to cover friction variation, wear, temperature and supply pressure changes. In clean service a factor of about 1.3–1.5 is common; abrasive, sticky or infrequently operated valves need more margin. When in doubt, ask the actuator supplier for their recommended factor for your duty.
Air Supply for Pneumatic Actuators
Pneumatic actuators need clean, dry compressed air at a stable pressure — commonly in the range of 4–8 bar, depending on the actuator. Check three things: the available air pressure at the actuator (not at the compressor), the air consumption per cycle for fast-cycling valves, and the air quality. Wet or oily air destroys seals and shortens actuator life; install filters and dryers where needed.
Failsafe and Spring Return
For safety loops, specify the required fail position: fail-open or fail-close. Spring-return pneumatic actuators size the spring to overcome the valve torque at the fail condition — this often requires a larger actuator than a double-acting one doing the same job. State the fail direction and the supply pressure when requesting a quote; the spring torque and air torque must both be checked against the valve requirement.
When to Ask a Manufacturer
If you cannot get a torque table, or the service is unusual — high temperature, sticky media, very fast cycling — send the details to the manufacturer rather than guessing. A correct quote needs: valve type and size, media, maximum differential pressure, temperature, operating frequency, available air pressure or power, and the required fail position.
Ask a Manufacturer Before You Spec
Langtuo Valve, a Shenzhen-based manufacturer with more than 15 years of experience and ISO 9001 certification, supplies pneumatic and electric actuated valves as matched packages — valve, actuator and accessories sized together — exported to over 30 countries. Send your service conditions through the contact page and we will confirm the actuator size with the torque calculation behind it.
An actuator that is undersized cannot move the valve; one that is oversized wastes money and can damage the valve. Actuator sizing is not a guess — it is a calculation based on the torque the valve needs at its hardest condition, plus a safety margin for real-world variation. This guide covers the essentials so you can specify actuated valves with confidence.
Why Actuator Sizing Matters
Valves need different amounts of force at different moments. Breaking the disc or ball away from the seat takes the highest torque; running torque and seating torque are lower. If the actuator is sized on average torque instead of breakaway torque, it will stall. If it is oversized, you pay for a bigger cylinder, motor and price, and the extra force can damage seats and stems.
Calculate the Required Torque
The total torque the actuator must deliver is the sum of:
- Valve breakaway torque — from the manufacturer data sheet, at the maximum differential pressure across the valve
- Packing and stem friction — increases with packing type and temperature
- Media effects — sticky, viscous or solids-laden media raise friction
Ask the valve manufacturer for the torque table, not a single number: torque changes with pressure, direction and temperature, and the worst case — usually the highest differential pressure — is what sizes the actuator.
Apply a Safety Factor
Once you have the required torque, multiply by a safety factor to cover friction variation, wear, temperature and supply pressure changes. In clean service a factor of about 1.3–1.5 is common; abrasive, sticky or infrequently operated valves need more margin. When in doubt, ask the actuator supplier for their recommended factor for your duty.
Air Supply for Pneumatic Actuators
Pneumatic actuators need clean, dry compressed air at a stable pressure — commonly in the range of 4–8 bar, depending on the actuator. Check three things: the available air pressure at the actuator (not at the compressor), the air consumption per cycle for fast-cycling valves, and the air quality. Wet or oily air destroys seals and shortens actuator life; install filters and dryers where needed.
Failsafe and Spring Return
For safety loops, specify the required fail position: fail-open or fail-close. Spring-return pneumatic actuators size the spring to overcome the valve torque at the fail condition — this often requires a larger actuator than a double-acting one doing the same job. State the fail direction and the supply pressure when requesting a quote; the spring torque and air torque must both be checked against the valve requirement.
When to Ask a Manufacturer
If you cannot get a torque table, or the service is unusual — high temperature, sticky media, very fast cycling — send the details to the manufacturer rather than guessing. A correct quote needs: valve type and size, media, maximum differential pressure, temperature, operating frequency, available air pressure or power, and the required fail position.
Ask a Manufacturer Before You Spec
Langtuo Valve, a Shenzhen-based manufacturer with more than 15 years of experience and ISO 9001 certification, supplies pneumatic and electric actuated valves as matched packages — valve, actuator and accessories sized together — exported to over 30 countries. Send your service conditions through the contact page and we will confirm the actuator size with the torque calculation behind it.