Belimo LF24-SR Spring-Return Damper Actuator 4 Nm, 2-10 V

Overview

The Belimo LF24-SR is a compact rotary actuator with a fail-safe spring return, made for positioning air dampers in ventilation and air-conditioning equipment. It produces 4 Nm from both the motor and the spring, which Belimo rates as suitable for dampers of up to approximately 0.8 m². Control is modulating with a 2 to 10 V signal, and a 2 to 10 V feedback output reports the damper position back to the controller. When the 24 V supply is interrupted, the spring drives the damper to its safe end position in less than 20 seconds.

Seven Star LLC supplies the Belimo LF24-SR for HVAC contractors, panel builders and maintenance teams in Oman and the GCC, with engineering support in Muscat for replacements and new installations. Because the same actuator fits many brands of air handling units, fan coil units and fresh air dampers, it is one of the most common spare parts on a building maintenance list.

Working Principle

Power and control arrive on a single four-core cable. As the controller raises the signal from 2 V towards 10 V, the motor rotates the shaft clamp towards the commanded angle and at the same time winds up the internal return spring. The Belimo LF24-SR compares the commanded and actual positions to within ±5 %, and the running time of the motor is 150 seconds for 90°, a slow, quiet movement that suits room comfort and air volume control. Sound power from the motor is 30 dB(A).

If the supply voltage is lost, for example during a power failure or when a fire alarm interlock removes the 24 V supply, the stored spring energy of the Belimo LF24-SR rotates the damper back to its fail-safe position. Belimo specifies a spring return time of under 20 seconds between -20 and 50 °C and under 60 seconds at -30 °C. The fail-safe direction is chosen by mounting the actuator left or right on the shaft, while the motor direction is selected with an L/R switch, so one model covers normally open and normally closed duties.

Engineering Design of the Belimo LF24-SR

The actuator mounts directly on the damper shaft with a universal clamp for round shafts of 8 to 16 mm, and an anti-rotation strap stops the housing from turning. The angle of rotation is up to 95° and can be limited mechanically to between 37 and 100 % of that range. There is no manual override on this model, so commissioning is done electrically, and a mechanical indicator shows the damper position. The enclosure is rated IP54, protection class III for safety extra-low voltage, and the device weighs 1.5 kg.

Electrical data are modest: AC 19.2 to 28.8 V or DC 21.6 to 28.8 V, 2.5 W while running, 1 W at rest and 5 VA for transformer sizing. Several Belimo LF24-SR units can be connected in parallel when the performance data are observed. The Belimo LF24-SR is rated for at least 60,000 fail-safe positions, and Belimo lists hygiene testing to VDI 6022 Part 1, meaning the housing can be cleaned and disinfected in air handling units with hygiene requirements.

Key Features

The Belimo LF24-SR is chosen where a damper must close or open safely without a separate power source:

• 4 Nm motor torque and 4 Nm spring torque for dampers up to about 0.8 m².
• Modulating 2 to 10 V control with 2 to 10 V position feedback for BMS monitoring.
• Spring return in under 20 seconds at -20 to 50 °C when power is removed.
• Fail-safe direction selectable by mounting, motor direction by L/R switch.
• Universal shaft clamp for 8 to 16 mm shafts with anti-rotation device included.
• Mechanical angle limitation from 37 to 100 % of the 95° travel.
• Low power draw of 2.5 W in operation and 1 W in the holding position.
• Minimum service life of 60,000 fail-safe positions, maintenance-free.

Industrial Applications

In the Gulf climate, outdoor air dampers on air handling units and dedicated outdoor air systems need to shut when the unit stops, otherwise hot, humid or dusty air flows into the ductwork and coils. The Belimo LF24-SR is widely used on these fresh air and exhaust dampers in offices, schools, hospitals, hotels and residential towers in Muscat, as well as on mixing dampers of packaged units and on small control dampers in fan coil plenums. A spring-return actuator also makes sense on dampers that protect cooling coils or keep pressure relationships between rooms when power is lost. For certified fire and smoke dampers, actuators approved for that duty should be used instead.

Where the damper needs feedback to a controller or building management system, the 2 to 10 V output of the Belimo LF24-SR can be read by a DDC controller, and accessories such as the S2A-F auxiliary switch or the Z-UIC signal converter for 4 to 20 mA extend the interface. Seven Star LLC supplies the actuator with mounting accessories for maintenance and retrofit work in Muscat, Sohar and Salalah. On the same air handling units, the Siemens QFM1660 duct humidity and temperature sensor and the Setra 264 low differential pressure transducer are typical companions.

Technical Specifications

The following figures for the Belimo LF24-SR are taken from the Belimo technical data sheet (en-gb, 2023-12-12):

How to Order

To order the Belimo LF24-SR, send Seven Star LLC the quantity, the damper size or required torque, the fail-safe direction and any accessories such as auxiliary switches or linkage kits. Our Muscat team will confirm the model against the Belimo data sheet, advise on stock and delivery within Oman and the GCC, and share the technical data sheet for your records. For chilled water pump control on the same projects, see the Schneider Electric Altivar 212 HVAC drive.