Double Acting and single acting (spring return) pneumatic actuators for industrial equipment application selectio

1. Double-acting actuator: Opening and closing are entirely dependent on compressed air to drive the piston. When the air source pressure is lost, the actuator will remain at the position it was in when the pressure was lost. The core is to ensure that sufficient torque is provided to drive the valve under the available air source pressure.
2. Single Acting(spring reset)actuator: An internally pre-compressed spring assembly serves as backup power. During normal operation, compressed air overcomes the spring force to drive the valve; when the air supply is lost, the spring energy is released, causing the valve to move to the preset safety position (usually closed or open).

How to make the selection based on the on-site working conditions

1. The working conditions that require the use of double acting actuators
   • Fault-free safety requirement: In the event of an interruption in the gas supply, the valve will remain in its original position and will not pose any safety risks.
   • Low cost, small installation space: Under the same torque output, the double-acting model has a simpler structure, a smaller volume and a lower cost.
2. The situation where single acting(spring return) actuator is selected
   • Safety integrity requirement: In the event of an interruption in the gas supply, the valve must automatically move to a specific safe position to prevent the leakage of hazardous media. For example: Hazardous media such as petroleum and natural gas, as well as chemical pipelines.

Application of safety factor: Ensure the reliability of actuator torque

After determining the type of actuator, precise torque calculation and application of safety factors are the core for ensuring long-term stable operation. Based on the documentation of AT Pneumatic Actuator Instruction 1.pdf, specific safety range is provided for different actuator types.

1.The selection of the double-acting actuator should take into account a safety factor of 20% to 30%. This factor is used to compensate for the following factors:

• Slight variations in frictional force.
• Common fluctuations in gas source pressure.
• Potential increase in valve operating torque over time (such as due to minor deposits). 
• Errors in calculation and measurement.

2.The selection of the spring reset actuator should take into account a safety factor of 30% to 50%. The higher coefficient requirement stems from its dual power source and higher reliability demands:

• Long-term use of spring torque leads to attenuation. 
• More stringent failure conditions.
• The influence of temperature changes on the performance of springs.

The systematic process of selecting pneumatic actuators

1.Determine the safety requirements for the valve, whether it should remain in its current position or automation reset in case of an air source failure.

2.Based on the selected type, use the corresponding safety factor range (double acting: 20%-30%; spring return: 30%-50%) to calculate the safety torque.

3.Based on the safety torque and in combination with the factory's air source pressure, select the corresponding pneumatic actuator model.