The Danfoss FQS series is a robust mechanical flow switch designed for reliable flow detection in liquid lines for water, glycol, and neutral brine. Its paddle-type mechanism is widely used in refrigeration systems, pumps, condensers, boilers, and other industrial equipment. When the flow rate exceeds the set threshold, the fluid displaces the paddle, actuating an internal microswitch that provides an SPDT (Single Pole Double Throw) contact output[reference:11].

Key Features

• Reliable Flow Detection: The paddle design provides a simple yet effective means of detecting flow/no-flow conditions across a wide range of pipe sizes.
• Versatile Adjustment: The switching point is easily adjustable to accommodate specific system requirements. Incremental (rising flow) and decremental (falling flow) adjustment values are provided for accurate setpoint configuration.
• High Pressure Rating: With a maximum working pressure of 10 bar (145 psig) and a burst pressure of 48 bar (696 psig), the FQS series is built to withstand demanding industrial conditions[reference:12].
• Wide Temperature Range: The device operates reliably in ambient temperatures from -25°C to 80°C and handles media temperatures from -5°C to 80°C[reference:13].
• Industry Certifications: The FQS series complies with CE and UKCA standards, ensuring suitability for use in various markets[reference:14].
• Easy Installation: The threaded connection (G1" R type) allows for straightforward integration into pipelines. The IP20 enclosure provides basic protection against solid foreign objects.

Flow Rate Adjustment Ranges

The FQS series offers adjustable flow set points for various pipe diameters (DN25 to DN150):

• DN25 (1 in): Decreasing 18-45 L/min, Increasing 21-50 L/min[reference:15].
• DN32 (1-1/4 in): Decreasing 43-100 L/min, Increasing 46-102 L/min[reference:16].
• DN40 (1-1/2 in): Decreasing 63-140 L/min, Increasing 68-145 L/min[reference:17].
• DN50 (2 in): Decreasing 50-250 L/min, Increasing 58-255 L/min[reference:18].
• DN65 (2-1/2 in): Decreasing 105-565 L/min, Increasing 120-570 L/min[reference:19].
• DN80 (3 in): Decreasing 100-850 L/min, Increasing 115-880 L/min[reference:20].
• DN100 (4 in): Decreasing 200-940 L/min, Increasing 210-950 L/min[reference:21].
• DN125 (5 in): Decreasing 350-1120 L/min, Increasing 380-1140 L/min[reference:22].
• DN150 (6 in): Decreasing 530-1700 L/min, Increasing 570-1800 L/min[reference:23].

Applications

The Danfoss FQS series is ideal for flow monitoring in HVAC, refrigeration, and industrial process applications, including pump protection (dry-run prevention), cooling system monitoring, heat exchanger flow control, and general liquid flow detection in water and glycol-based systems.