In the previous article, we examined the structure, operating principle and distinctive torque curve of scotch-yoke pneumatic actuators. This article discusses their main advantages, applications and the key points to consider when selecting one.

1. Main Advantages of Scotch-Yoke Actuators

  1. High torque output: At the same cylinder diameter and air supply pressure, a scotch-yoke actuator can deliver more torque than a rack-and-pinion design, making it particularly suitable for large valves.
  2. Torque perfectly matched to the valve load: The scotch-yoke torque curve is high at both ends and lower in the middle. It closely matches the torque demand of ball and butterfly valves, improving energy efficiency.
  3. Simple construction and high reliability: Fewer components make maintenance convenient and provide long service life in applications with frequent switching.
  4. Fast response: The scotch-yoke mechanism provides rapid pneumatic response and high control accuracy, with stable operation in harsh environments.
  5. Choice of materials: Aluminium alloy, stainless steel, carbon steel and other versions can be selected to suit different corrosive media and environments.
  6. Flexible single-acting/double-acting configurations: Available as single-acting with spring return or double-acting to meet different safety and control requirements.

2. Applications

Large-diameter ball valves, butterfly valves and plug valves

High differential-pressure applications requiring high closing torque

Long-distance oil and natural gas pipelines

Process-control industries such as chemicals and power generation

3. Selection Considerations

Torque matching: The scotch-yoke torque curve varies, so confirm that the torque at the end of travel meets the valve's closing torque requirement.

Air supply pressure: Ensure that the available pressure is within the actuator's rated operating range, typically 4-8bar.

Action type: Select single-acting spring-return or double-acting operation according to safety requirements.

Material selection: Choose aluminium alloy, stainless steel or carbon steel according to the process medium and environment.

4. Single-Acting and Double-Acting Configurations

Scotch-yoke actuators can be configured in either single-acting or double-acting form:

Single-acting scotch-yoke: Air power opens the valve, and spring return closes it. Suitable for applications requiring fail-safe protection.

Double-acting scotch-yoke: Air power drives both opening and closing, while a directional valve switches the air supply. It produces greater force and suits applications with higher torque requirements.

With their high torque and a torque curve closely matched to valve loads, scotch-yoke pneumatic actuators offer clear advantages for large diameters and high differential pressures. Understanding these characteristics helps you select more appropriately.

Zhejiang HES Automatic Instrument & Valve Co., Ltd.

Founded in 1989 · Over thirty years focused on pneumatic actuators