How Does a Spring Return Actuator Work?

Dec 17th 2020

How Does an Actuator Work?

An actuator is a control mechanism that is operated by an energy source. A valve actuator works as the power source for a valve. There are two ways you can control an actuator: manually or automatically. Manual options are powered by people, while automatic actuator power sources can be:

  • Electric
  • Pneumatic
  • Hydraulic

The automatic type of actuator is ideally suited for installations in which human interaction is either dangerous or not possible, such as a challenging space or installation location.

Actuators can be fabricated to stay open in the case of failure or stay closed. They also come in quarter-turn or linear versions, depending on the application. All power actuators are either spring return or double acting.

What is the Difference Between Spring Return and Double Acting Types of Actuators?

The names of these two types of actuators provide clues as to how they function; a single spring return supplies power for one direction, while the double acting actuator supplies power for both working directions. The spring return actuator uses spring force on one side to either open or close the valve, and the double acting actuator uses a piston that is pressurized on both sides.

Spring Return Actuator

Spring return actuators have either air or liquid supplied to one side of the piston, and the energy to move the valve comes from a spring on the opposite side. This pressure of the air or liquid opens or closes the valve, and a spring creates the opposite motion. The design of the spring return type of actuator makes it ideal for situations where the torque load is experienced on only one side, at the activation stroke. Also, the simpler design and higher reliability of a spring return is best for applications where an immediate shutdown is necessary for safety.

Double Acting Actuator

Double acting actuators have air or liquid supplied to both sides of the piston. One side is set at a higher pressure to create the movement that activates the valve. The pressure of the air or liquid opens and closes the valve. This type of actuator works great in situations where there are high torque loads in both working directions. It's also the preferred type of actuator when there is a high thrust strength, such as in petroleum and natural gas applications.

If your machinery needs to have a valve remain in its last position when it loses a signal or power, the double acting actuator is the better choice because the pressurization on both of its sides will keep the valve secured in the last position.

Benefits of Belimo Spring Return Actuators

Belimo actuators are designed with multiple torque offerings which can be used in a wide variety of HVAC damper applications such as:

  • Control dampers
  • Air handlers
  • Economizer units
  • VAV terminal units
  • Fan coil units
  • Fan shutters
  • Unit ventilators

Other Belimo Advantages

  • Safety: Offers the most reliable safety because of its true mechanical spring return.
  • Installation: Includes a manual override crank for ease of installation.
  • Power: Low power consumption results in higher efficiency and the need for smaller transformer size.
  • Performance: Minimum torque is guaranteed over the entire range to prevent loss in performance due to temperature or power supply voltage fluctuations.

We carry a vast selection of Belimo actuators, including the Belimo AFB24-SR. This highly-rated product mounts directly to the damper shaft with a universal clamp and provides fail-safe control in HVAC systems. The brushless DC motor of the Belimo AFB24-SR uses a microprocessor that is application specific, preventing damage to the actuator due to stalling.

Which Type of Actuator Is Right for You?

Now that you know the difference between a double acting and a spring return actuator, you'll be able to decide which type of actuator is the best for your machine.

For more information about selecting the right type of actuator for your specific needs, contact our HVAC specialists today.

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