AFB24-SR-S Belimo Actuator


Damper Actuator, 180 in-lb [20 Nm], Spring return, AC/DC 24 V, 2…10 V, 2 x SPDT (AFX24-SR-S)

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The  Belimo AFB24-SR-S modulating damper actuator, spring return, reversable with CW/CCW mounting (AFX24-SR-S)


Installation Guide


For fail-safe, modulating control of dampers in HVAC systems. Actuator sizing should be done in accordance with the damper manufacturer’s specifications. The actuator is mounted directly to a damper shaft up to 1.05” in diameter by means of its universal clamp. A crank arm and several mounting brackets are available for applications where the actuator cannot be direct coupled to the damper shaft. The actuator operates in response to a DC 2…10 Vor, with the addition of a 500Ω resistor, a 4…20 mA control input from an electronic controller or positioner. A DC 2…10 V feedback signal is provided for position indication. A common installation technique for control of multi-section dampers is to use the U5 position feedback of one actuator (Master) to control multiple actuators (Slaves). Belimo refers to this as Master/Slave control. The only requirement is that the actuators are installed on MECHANICALLY SEPARATE damper shafts.


The AF..24-SR-S series actuators provide true spring return operation for reliable fail-safe application and positive close off on air tight dampers. The spring return system provides constant torque to the damper with, and without, power applied to the actuator. The AF..24-SR-S series provides 95° of rotation and is provided with a graduated position indicator showing 0° to 95°. The AF..24-SR-S uses a brushless DC motor which is controlled by an Application Specific Integrated Circuit (ASIC) and a microprocessor. The microprocessor provides the intelligence to the ASIC to provide a constant rotation rate and to know the actuator’s exact fail-safe position. The ASIC monitors and controls the brushless DC motor’s rotation and provides a digital rotation sensing function to prevent damage to the actuator in a stall condition. The actuator may be stalled anywhere in its normal rotation without the need of mechanical end switches. The AF..24-SR-S versions are provided with two built-in auxiliary switches. These SPDT switches provide safety interfacing or signaling, for example, for fan start-up. The switching function at the fail-safe position is fixed at 10°, the other switch function is adjustable between 10° to 90°. The AF..SR-S actuator is shipped at 5° (5° from full fail-safe) to provide automatic compression against damper gaskets for tight shut-off. ATTENTION: AF..24-SR-S cannot be tandem mounted on the same damper or valve shaft. Only On/Off and MFT AF.. models can be used for tandem mount applications.


  • Actuator Type
    • Spring return
  • Angle of Rotation
    • 95°
  • Auxiliary Switches
    • 2 x SPDT
  • Control Type
    • Modulating
  • Degree of Protection
    • IP54, NEMA 2, UL Enclosure Type 2
  • Direction of Rotation (Fail-Safe)
    • Reversible with cw/ccw mounting
  • Electrical Connection
    • Cable
  • Manual Override
    • 5 mm hex crank (3/16″ Allen), supplied
  • Power Consumption (Holding)
    • 3 W
  • Power Consumption (Running)
    • 5 W
  • Running Time (Fail-safe)
    • <20 s
  • Running Time (Motor)
    • 95 s
  • Safety Function
    • YES
  • Shaft Diameter
    • 1/2…1.05″ round, centers on 1/2″ and 3/4″ with insert, 1.05″ without insert
  • Torque
    • 180 in-lb [20 Nm]
  • Voltage AC/DC
    • AC/DC 24 V


Additional information

Weight 8 lbs
Dimensions 2 × 2 × 2 in
Part Number