Sizing: Spring Return Actuators

The suggested safety factor for spring return actuator under normal working conditions is 30-50% 

Example： 

The torque needed by valve=80N.m 

The torque consider safety factor ( 1+30%)=104N.m 

Air Supply=5Bar

According to the table of spring return actuators' output, we find output torque of RT435SR K7 is: 

Air stroke 0°=308N.m 

Air stroke 90°=247N.m 

Spring stroke 90°=181N.m 

Spring stroke 0°=120N.m 

All the output torque is larger than we needed.

Attention

During the restoration, the spring return actuators'  output torque will not be affected by the inputing air  from the port B. On the contrary, it will help the  restoration of springs.

During selecting the spring return actuators, we can  choose the more reasonable and more economical  actuators, if we konw the different torque needed by the  valve working at opening, operating and closing.

Example: 

The max torque needed by the butterfly valve=104N.m 

The torque after opened (operating)104x30%=32N.m 

Air Supply=5Bar 

We can select the RT255SR K11 

output torque is:  Air stroke 0%136N.m >104N.m 

Air stroke 90o=78N.m >32N.m 

Spring stroke 90o=173N.m >32N.m

Spring stroke 0o=115N.m >104N.m 

The above datas show the actuator's torque can  satisfy the requirement of the butterfly valve.

Make sure that the torque necessary to operate the  valve is compatible with the actuator torque (it  depens on both actuator type and air supply). Please note that the requested torque depends not  only on the valve,but on the working conditions  and the safety margins of the plant in question,too.