Danfoss LLG 740 S Flow Switch | Paddle Type, 1/2" to 2", 0-16 bar, 5A, SPDT Specs

Danfoss LLG 740 S Flow Switch | Paddle Type, 1/2" to 2", 0-16 bar, 5A, SPDT Specs

Danfoss LLG 740 S flow switch specifications. Paddle-type flow monitor, 1/2" to 2" sizes, 0-16 bar, SPDT 5A/250V relay. For water and neutral liquid flow detection.

Product Overview

The Danfoss LLG 740 S​ is a paddle-type mechanical flow switch​ designed to monitor the presence or absence of flow in liquid pipelines. This model features a single-pole double-throw (SPDT) microswitch, operates within a 0-16 bar pressure range, and is available in pipe sizes from 1/2" to 2". The "LLG 740 S" designation identifies this specific model in Danfoss's LLG flow switch series. This device provides a reliable electrical signal based on fluid flow, used for pump protection, alarm systems, and process control in water and neutral media applications.

Technical Specifications

Note: Specifications are based on Danfoss LLG series documentation. The "S" in LLG 740 S may indicate a specific variant (e.g., with standard microswitch). The exact set point range is dependent on the pipe size and specific paddle configuration.

Key Features

• Adjustable Set Point:​ The trip point (flow rate for switch actuation) is field-adjustable via an external dial or screw.

• SPDT Microswitch:​ Provides both NO and NC contacts for flexible wiring (e.g., for alarm or run confirmation).

• Robust Brass Body:​ Chrome-plated for corrosion resistance in water applications.

• Media-Compatible Paddles:​ Available in stainless steel for general use or POM (polyoxymethylene) for aggressive media.

• Bidirectional Flow:​ Can detect flow in either direction, with optimal performance in the marked direction.

• Easy Installation:​ Screws directly into a threaded tee in the pipeline. No external power required for operation.

• Visual Indicator:​ Often includes a visual flag to indicate paddle position/flow status.

Flow Setting and Performance

• Set Point Adjustment:​ Made by turning an adjustment screw on the switch housing, which changes the spring tension on the paddle.

• Typical Setting Range:​ The adjustable flow velocity range depends on the pipe size. For example, in a 1" model, it might be adjustable from ~0.15 to 1.5 m/s.

• Hysteresis:​ The switch has a built-in deadband (hysteresis) to prevent rapid switching (chatter) when the flow is near the set point.

Typical Applications

• Pump Protection:​ Prevents pump dry-running by detecting no-flow conditions.

• Cooling Circuit Monitoring:​ Ensures flow in machine tool cooling systems, chillers, or heat exchangers.

• HVAC Systems:​ Monitors flow in heating/cooling water circuits, and signals pump failure.

• Water Treatment:​ Flow confirmation in filtration, dosing, or backwash cycles.

• Process Control:​ Interlock for processes requiring a minimum flow rate.

• Alarm Systems:​ Triggers an alarm for loss of flow in fire sprinkler test lines or other critical systems.

Important Technical Notes

1. Proper Sizing:​ The flow switch must be ordered for the correct pipe size​ (e.g., LLG 740 S for 1" pipe). Using an incorrectly sized paddle affects accuracy and may cause damage.

2. Installation Location:​ Install in a straight pipe run, typically 10 pipe diameters downstream and 5 diameters upstream​ of any disturbance (elbow, valve, pump) for stable flow profile.

3. Media Compatibility:​ Confirm that the paddle and seal materials (standard EPDM, optional FKM) are compatible with the fluid media (water, glycol mixtures, oils, etc.).

4. Adjustment:​ Set the trip point with the system running at the desired minimum flow rate. Tighten the adjustment screw until the switch actuates, then add a small safety margin.

5. Electrical Load:​ The microswitch is rated for 5A/250V AC. Do not exceed this rating. For higher loads, use the switch to control a relay or contactor.

6. Mounting Orientation:​ For horizontal pipes, the switch should be mounted on the side (3 o'clock or 9 o'clock position) to prevent sediment buildup on the paddle. For vertical pipes, flow should be upward.

Note: This data sheet provides general specifications for the Danfoss LLG 740 S flow switch. For complete selection guidelines (including flow setting curves for each pipe size), installation drawings, and wiring diagrams, consult the official Danfoss LLG Series Technical Documentation​ for the specific size and configuration required.