What is the difference between a spring return, non-spring return, and electronic fail-safe actuator

All of the actuators need power to operate, what happens if the supplied power is disrupted? Until power is restored, a regular electric actuator will still get stuck in the same position in spite of changing the demand from HVAC side. If an outside air damper stops in the open position on a very cold day, the coils inside the air handler could freeze and break, causing extensive damage.

To solve the issue of non-failsafe actuators, spring-return actuators have been started using. As an electric actuator drive a load, it also tensions a mechanical spring. To maintain the desired position, the power had to be continuously supplied. When the electrical power failed, the spring will return the actuator to its original(failsafe) position. In this spring return fail-safe set up of a particular standard electric actuator, the torque had to be essentially doubled to overcome the resistance of the spring in addition to the load. The greater the torque of the actuator, the more initial cost of the actuator together with more power consumption.

Another innovation which comes after spring return is the more convenient, durable, consistent, and energy efficient solution: electronic failsafe actuators which are used capacitors to store energy instead of springs. Capacitors are electronic devices that store electric charge and require very little current to hold continuously charged whenever the power is supplied. When supplied power fails, the charge which is stored in the capacitor is used to drive the actuator back its original position (fail-safe position). Therefore, they do not need to use extra power compared to spring-return actuators which require more toque to overcome spring resistance on every cycle.

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