Belimo LFX24-SR-S Spring Return Damper Actuator 35 in-lb 24V Modulating with Auxiliary Switch

The Belimo LFX24-SR-S is a direct-coupled, spring return damper actuator designed for fail-safe, modulating control of air dampers in HVAC and building automation systems. Rated at 35 in-lb (4 Nm) of torque, it operates on AC/DC 24V power and accepts a 2–10 VDC proportional control signal, or a 4–20 mA signal with the addition of a 500Ω resistor accessory.

Key Features:

• Spring Return Fail-Safe: Returns the damper to a pre-defined safe position on power loss, with consistent torque delivered with or without power applied
• Brushless DC Motor: Controlled by an Application Specific Integrated Circuit (ASIC) and microprocessor for constant rotation rate and precise fail-safe positioning
• Stall Protection: Digital rotation sensing prevents actuator damage in a stall condition — no mechanical end switches required
• 95° Rotation: Graduated position indicator displays 0 to 95° for easy visual confirmation
• Built-In Auxiliary Switch (1x SPDT): Adjustable between 0° and 95° for safety interfacing, fan start-up signaling, or end-position indication; double insulated — no electrical ground required
• Modulating Control: Responds to 2–10 VDC input; 4–20 mA compatible with ZG-R01 500Ω resistor accessory
• Position Feedback: 2–10 VDC feedback signal provided for position indication or master-slave applications
• Direct Coupled Mounting: Mounts directly to damper shafts from 3/8" to 1/2" diameter (1/2" centered at delivery); use K6-1 accessory for shafts up to 3/4"
• Low Power Consumption: 2.5W running, reduced to 1W in holding mode
• Galvanized Steel Housing: NEMA 2 rated, UL 2043 compliant for use in air plenums per NEC Section 300.22(C)
• Maintenance-Free: cULus listed, ISO 9001 manufactured, 5-year warranty

Operating temperature range is -22°F to 122°F (-30°C to 50°C). The LFX24-SR-S is ideal for proportional damper control in commercial HVAC, building automation systems (BAS), and air handling unit applications where reliable spring return fail-safe operation is required.