Spring-return and non-spring return actuators are two common types of actuators used in control systems to operate valves, dampers, or other mechanical devices. These actuators differ in their mechanism for returning to their default or resting position when the control signal is removed. Here's a brief explanation of each:

1. Spring-Return Actuator:

   • A spring-return actuator, also known as a spring-loaded actuator or fail-safe actuator, incorporates a spring mechanism to return the actuator to its default position when the control signal is removed or lost.
   • When the actuator receives a signal to move to a specific position (e.g., open or close a valve), it compresses or expands the spring to move the actuator to the desired position.
   • In the absence of the control signal (e.g., due to power loss or signal failure), the spring force overcomes the control force, causing the actuator to return to its default position (typically the fully closed or fully open position).
   • Spring-return actuators are commonly used in applications where fail-safe operation is critical, such as safety shutdown systems, emergency ventilation systems, or fire protection systems.

2. Non-Spring Return Actuator:

   • A non-spring return actuator, also known as a direct-drive actuator or power-open/power-close actuator, does not rely on a spring mechanism to return to its default position.
   • Instead, the actuator maintains its position using continuous power from the control signal. It remains in the last commanded position until a new command is received.
   • Non-spring return actuators are typically used in applications where fail-safe operation is not required or where the actuator must maintain its position in the event of power loss.
   • These actuators may be equipped with position feedback sensors to provide feedback on the actuator's position to the control system.

In summary, spring-return actuators use a spring mechanism to return to their default position when the control signal is lost, providing fail-safe operation in critical applications. Non-spring return actuators maintain their position using continuous power from the control signal and do not rely on a spring mechanism for returning to the default position. The choice between spring-return and non-spring return actuators depends on the specific application requirements, including safety considerations, power availability, and control system design.