The Belimo AFB24-SR-S is a spring-return (fail-safe) damper actuator delivering 180 in-lb [20 Nm] of torque with modulating 2-10 VDC on 24 VAC/DC power. It direct-couples to damper shafts up to 1.05 in. diameter and drives to a mechanical fail-safe position on power loss, making it a proven member of the AFB spring-return platform for commercial HVAC damper control. Two built-in SPDT auxiliary switches signal end position or interlock equipment.
Specifications sourced from the official Belimo AFB24-SR-S technical data sheet (rev 2026-03-09).
Overview
Belimo AF-Series actuators are spring-return (fail-safe) drives for commercial HVAC dampers. The AFB24-SR-S produces 180 in-lb [20 Nm] of torque, mounts directly to the damper shaft, and On loss of power the spring drives the damper to its defined fail-safe position within the rated fail-safe time. A 2-10 VDC (or 4-20 mA with the ZG-R01 resistor) signal modulates the damper, with matching 2-10 VDC position feedback.
Best for
- VAV and modulating damper control
- Building-automation 2-10 VDC control loops
- Fail-safe spring-return damper applications
- End-position signaling or equipment interlock
Key Features
True Spring Return Fail-Safe
Constant-torque spring drives the damper to a defined safe position on power loss — no mechanical end switches required, and positive close-off on air-tight dampers.
180 in-lb Torque
Sizes a wide range of commercial dampers; up to two AF actuators can be piggybacked for loads to 266 in-lb on a 3/4" minimum shaft.
Modulating 2-10 VDC
Accepts a 2-10 VDC (or 4-20 mA with ZG-R01) control signal with matching 2-10 VDC position feedback for precise modulation.
Two Built-In Aux Switches
2x SPDT auxiliary switches (one fixed, one adjustable) signal damper position or interlock fans, lights and other equipment.
Plenum-Rated & Quiet
UL 2043 plenum rated for use in air-handling spaces, double-insulated (Class 2), cULus listed and built to ISO 9001.
Technical Specifications
| Parameter | Specification |
|---|---|
| Manufacturer | Belimo |
| Part Number | AFB24-SR-S |
| Actuator Type | Spring-Return (Fail-Safe) Damper Actuator |
| Nominal Voltage | AC/DC 24 V |
| Nominal Voltage Range | AC 19.2-28.8 V / DC 21.6-28.8 V |
| Nominal Frequency | 50/60 Hz |
| Power Consumption (Running) | 5.5 W |
| Power Consumption (Holding) | 3W |
| Transformer Sizing | 8.5 VA |
| Torque | 180 in-lb [20 Nm] |
| Control Signal | Modulating |
| Operating Range (Y) | 2-10 VDC (4-20 mA with ZG-R01 resistor) |
| Input Impedance | 100 kohm (2-10 V) / 500 ohm (4-20 mA) |
| Position Feedback (U) | 2-10 VDC (max. 0.5 mA) |
| Angle of Rotation | 95° (adjustable end stop 35-95°) |
| Running Time (Motor) | 95 s / 90° |
| Running Time (Fail-Safe) | <20 s @ -4 to 122°F [-20 to 50°C]; <60 s @ -22°F [-30°C] |
| Auxiliary Switches | 2x SPDT, 1 mA-3 A (0.5 A inductive), DC 5 V-AC 250 V |
| Manual Override | 5 mm hex crank (3/16" Allen), supplied |
| Direction of Motion | Selectable CW/CCW |
| Position Indication | Mechanical |
| Electrical Connection | 18 AWG appliance cable, 3 ft [1 m], 1/2" NPT conduit connector |
| Overload Protection | Electronic, full 0-95° rotation |
| Electrical Protection | Double insulated (Class 2) |
| Enclosure Rating | NEMA 2 / IP54 / UL Type 2 |
| Housing Material | UL94-5VA |
| Ambient Temperature | -22 to 122°F [-30 to 50°C] |
| Storage Temperature | -40 to 176°F [-40 to 80°C] |
| Agency Listing | cULus (UL60730-1A / -2-14, CAN/CSA) |
| Quality Standard | ISO 9001 |
| Plenum Rated | UL 2043 (suitable for air plenums) |
| Weight | 5.7 lb [2.6 kg] |
| Warranty | 5 Years |
Documentation
Related Products
Accessories & Mounting
Common Belimo accessories for mounting, linkage, signaling and powering the AFB24-SR-S, drawn from the actuator datasheet. All are stocked by ZOT Supply as an authorized Belimo distributor.
Mounting & Linkage
Electrical Add-Ons
Frequently Asked Questions
What is the Belimo AFB24-SR-S?
The Belimo AFB24-SR-S is a spring-return (fail-safe) damper actuator for commercial HVAC. It produces 180 in-lb [20 Nm] of torque, uses modulating 2-10 VDC control on 24 VAC/DC power, and drives the damper to a mechanical fail-safe position on loss of power. Its housing is rated NEMA 2 / IP54 / UL Type 2.
How does the AFB24-SR-S fail safe on power loss?
The AFB24-SR-S stores energy in a return spring during normal operation. When power is lost, the spring drives the damper to its defined safe position — no capacitors or batteries, and no mechanical end switches required. It is shipped pre-tensioned about 5° for tight shut-off on gasketed dampers.
What torque does the AFB24-SR-S provide and what shaft sizes does it fit?
It delivers 180 in-lb [20 Nm] and direct-couples to round or square damper shafts up to 1.05 in. diameter using its universal clamp. Up to two AF actuators can be piggybacked for loads to 266 in-lb on a 3/4 in. minimum shaft.
What control signal does the AFB24-SR-S use?
It uses modulating 2-10 VDC control. The 2-10 VDC input also accepts 4-20 mA with the ZG-R01 resistor and provides 2-10 VDC position feedback.
What is the running time of the AFB24-SR-S?
Motor running time is about 95 seconds for 90° of travel, and the spring-return fail-safe time is under 15 seconds at normal temperatures (under 60 seconds at -22°F [-30°C]).
Does the AFB24-SR-S have auxiliary switches?
Yes. It has two built-in SPDT auxiliary switches (rated 1 mA to 3 A, DC 5 V to AC 250 V) — one fixed and one field-adjustable — for end-position signaling or interlocking fans, lights and other equipment.
Is the AFB24-SR-S UL listed for damper control?
Yes. The AFB24-SR-S is cULus listed to UL60730 and CAN/CSA, is double-insulated (Class 2), and is UL 2043 plenum-rated for installation in air-handling spaces.
Is the Belimo AFB24-SR-S available from an authorized Belimo distributor?
Yes. ZOT Supply is an authorized Belimo distributor and carries the AFB24-SR-S. Every unit ships factory-new with Belimo's full 5-year warranty and application support from our team.
- Actuator Type:
- Spring Return
- Torque:
- 180 in-lb
- Control Signal:
- Modulating
- Voltage:
- 24 VAC/DC
- Auxiliary Switch:
- Yes
- NEMA 4X Enclosure:
- No
- Series:
- AFB
- Feedback Signal:
- 2-10 VDC
