The Belimo FSAF230A-S is a spring-return (fail-safe) actuator designed to operate UL555 and UL555S listed fire/smoke dampers in ventilation and air-conditioning systems.
It is typically mounted so the damper is in the fail-safe position (commonly closed); when power is applied, the actuator drives the damper to the open position while tensioning the internal spring. If power is interrupted, the spring drives the damper back to the fail-safe position.

The “-S” version includes two integrated auxiliary switches (2x SPST) for end-position indication and interlock control.

Applications

• Operation of UL555 / UL555S fire and combination fire/smoke dampers in HVAC systems
• Fail-safe damper control (spring return to safety position on power loss)
• End-position feedback / interlocks using the built-in auxiliary switches