In industrial automation, pneumatic actuators are commonly divided into the following types according to their structure and operating principle. Each has distinct advantages and suitable operating conditions. Choosing the right type makes the work more effective.

1. Rack-and-pinion pneumatic actuators

This is currently the most widely used pneumatic actuator type, including the HES AT (DRSC) series. Compressed air pushes two pistons outward in a straight line. Racks on the pistons rotate a central pinion shaft, converting linear movement into 90-degree rotation to open or close ball or butterfly valves.

  • Main features

Compact, small and lightweight.

Smooth output torque and high efficiency, with energy conversion efficiency reaching more than 70%.

Symmetrical dual-piston design eliminates lateral forces and extends seal life.

A standardized model range covers different valve sizes.

Standard mounting interfaces (ISO 5211 / NAMUR) provide broad compatibility.

  • Applications

Frequent opening and closing in petrochemical, natural gas, power generation and water treatment applications; especially suitable for ball and butterfly valves.

2. Scotch-yoke pneumatic actuators

A scotch-yoke pneumatic actuator is a common rotary actuator. Its scotch-yoke mechanism converts the cylinder's linear motion into rotation to open and close a valve.

  • Main features

High output torque, especially suitable for large-diameter ball and butterfly valves.

Maximum torque at the moment of valve closing ensures reliable sealing.

Simple construction with few components; long-life design suitable for frequent switching.

Wide range of travel adjustment.

  • Applications

High-torque applications such as large-diameter valves, high differential pressures, pipeline transport, and oil and gas production.

3. Diaphragm pneumatic actuators

A diaphragm actuator uses a flexible diaphragm to transmit force. Air pressure displaces the diaphragm, which moves the valve stem.

  • Features

Fast response, less than 0.5 seconds, suitable for modulating service.

Relatively short stroke, generally less than 100mm, suitable for small-diameter valves.

Good sealing without leakage.

Output force has a nonlinear relationship with stroke.

The diaphragm has a limited service life and requires periodic replacement.

  • Applications

Continuous modulation, process control, chemical processing, power generation and other applications requiring fast response. With a valve positioner, high-precision regulation within ±0.5% is possible.

4. Piston pneumatic actuators (linear)

A piston actuator uses compressed air to move a piston linearly inside a cylinder, directly driving the valve stem to open or close the valve.

  • Features

High output thrust for large-diameter valves.

Long or short strokes to meet different valve requirements.

Double-acting versions offer balanced thrust and precise positioning.

Mature design and high reliability.

Optional cushioning reduces impact at the end of travel.

  • Applications

Gate valves, globe valves and other valves requiring linear displacement, as well as high-pressure applications requiring high thrust.

5. How to choose the right type

By valve type

Quarter-turn valves (ball and butterfly valves) → choose rack-and-pinion or scotch-yoke.

Linear valves (gate and globe valves) → choose piston or diaphragm.

By torque/thrust requirements

Low torque → rack-and-pinion.

Medium torque → scotch-yoke.

High torque → AW series or large scotch-yoke actuators.

By control mode

On/off control → all actuator types can be used.

Modulating control → diaphragm plus valve positioner, or rack-and-pinion plus smart valve positioner.

By environmental conditions

Explosion protection requirements → pneumatic actuators offer an inherent explosion-protection advantage.

Corrosive environments → choose stainless steel or specially coated materials.

Knowing the characteristics and applications of different actuator types makes selection more straightforward.

Zhejiang HES Automatic Instrument & Valve Co., Ltd.

Established in 1989 · Focused on pneumatic actuators for more than three decades

Products include AT, HG and AW series pneumatic actuators