Flow Switches

A flow switch are flowmeter devices used to measure the flow rate and pressure of liquid, gas or vapour that passes through them. They measure flow rates over a set time, or they can continually measure the medium passed through. They operate by sending signals to another component elsewhere in the system (e.g. pumps) telling it to stop/start in order to adjust flow rate and pressure to the desired and programmed levels.


Common types of flow switches


  • Water: uses a paddle (physical or ultrasonic), for water pumps and sprinklers.

  • Gas and air: HVAC and ducting, paddle air, boilers, inline air flow switches

  • Thermal dispersion: involves a sensor probe, allows the rate of gas or liquid flow to be calculated according to how quickly heat is carried away by the molecules flowing past.

  • Oil: can operate at higher temperatures with robust seals and housing.

  • Ultrasonic, Magnetic: emits an ultrasonic signal to the medium, this is then bounced back and converted by the primary device. Commonly used in dirty applications such as wastewater

  • Mechanical: need to be tested regularly as continual movements of parts will lead to wear and tear.

  • PVC: basic type ideal where a quick visual confirmation of flow/no flow status is needed. Designed for cleaning and maintenance.

  • Industrial: larger more robust so can withstand higher volumes, pressure and flow rates, designed for heavily contaminated or hazardous materials.

  • Pneumatic: for applications where there is a necessary pressure differential between different areas of ducting.

  • Adjustable: quickly and easily recalibrate the desired flow settings

  • Rotary: functions as a basic turbine, ideal for low flow liquid monitoring.

Some basic rules to install a flow switch:


  • Install on a straight section of pipe or duct

  • Make sure there is a good length of straight pipe in front and behind the switch

  • Avoid fitting or wiring near to bends, other fittings, valves, drains, narrower or wider sections of pipe

Each type of flow switch has its own specific applications and installation constraints. The way to select the right one is to think about the application as a guide, not the technology. Starting with the application, will help to select the technology based on accuracy, cost, durability and reliability, rather than trying to make the technology fit the application you have.


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Description Price Media Monitored Device Type Minimum Flow Rate Maximum Flow Rate Supply Voltage Pipe Diameter Range Connection Type Maximum Pressure Material Minimum Media Temperature Maximum Media Temperature Minimum Operating Temperature Maximum Operating Temperature Current Rating
RS Stock No. 256-578
HK$453.86
Each
units
Liquid Control Valve 3 L/min 6 L/min 240 V ac 22 mm - 10bar - +5 °C +85°C +5°C +70°C -
RS Stock No. 395-7230
Mfr. Part No.020-3497
HK$2,388.99
Each
units
Liquid Paddle 15 L/min 125 L/min 250 V 1 in 1 BSP 55bar Brass - - -18°C +100°C -
RS Stock No. 395-6962
Mfr. Part No.166702
HK$309.05
Each
units
Liquid Piston - 1 L/min 120 → 240 V ac/dc 1/4 in 1/4 BSP 10bar Noryl - +100°C - +100°C -
RS Stock No. 256-562
HK$380.00
Each
units
Liquid Control Valve 3 L/min 6 L/min 240 V ac 15 mm - 8bar - +5 °C +85°C +5°C +70°C -
RS Stock No. 613-4238
BrandRS PRO
HK$1,387.77
Each
units
Gas, Liquid Paddle 5.5 L/min 7 L/min 250 V ac 15 mm 1/2 BSP Female 25bar Nickel Plated Brass - +110°C - +110°C 5 A
RS Stock No. 906-7734
Mfr. Part No.V4-2-U
HK$3,042.36
Each
units
Air, Liquid Vane Operated 8 (liquid) gal/min, 32 (Air) gal/min 15 (liquid) gal/min, 65 (Air) gal/min 125/250 V ac 2 in 1-1/2 NPT Male 69bar Brass -20 °C +73°C -20°C +73°C 10 A
RS Stock No. 395-7218
Mfr. Part No.020-3490
HK$2,194.33
Each
units
Liquid Shuttle 19 L/min 57 L/min 250 V 1 in 1 BSP 27bar Bronze - - -20°C +80°C -
RS Stock No. 395-6940
Mfr. Part No.166701
HK$357.50
Each
units
Liquid Piston - 0.2 L/min 120 → 240 V ac/dc 1/4 in 1/4 BSP 10bar Noryl - +100°C - +100°C -
RS Stock No. 395-7016
Mfr. Part No.166703-A
HK$318.75
Each
units
Gas Piston - 158 L/min 120 → 240 V ac/dc 1/4 in 1/4 BSP 10bar Noryl - +100°C - +100°C -
RS Stock No. 744-0913
Mfr. Part No.PFM710S-C4-A-W
BrandSMC
HK$2,340.00
Each
units
Dry Air, Gas Integrated Display 0.2 L/min 10 L/min 24 V dc 4 mm One-Touch Fitting 750kPa PBT 0 °C +50°C 0°C +50°C -
RS Stock No. 395-7202
Mfr. Part No.020-3491
HK$2,438.14
Each
units
Liquid Shuttle 7.5 L/min 30 L/min 250 V 1 in 1 BSP 27bar Bronze - - -20°C +80°C -
RS Stock No. 395-7038
Mfr. Part No.166704-A
HK$359.01
Each
units
Gas Piston - 340 L/min 120 → 240 V ac/dc 1/4 in 1/4 BSP 10bar Noryl - +100°C - +100°C -
RS Stock No. 122-8443
Mfr. Part No.51590
HK$2,373.75
Each
units
Liquid Piston - 0.5 gal/min - 1/4 in 1/4 NPT Female 69bar Brass - - -29°C +148.9°C -
RS Stock No. 122-8444
Mfr. Part No.51594
HK$2,373.75
Each
units
Liquid Piston - 0.75 gal/min - 1/4 in 1/4 NPT Female 69bar Brass - - -29°C +148.9°C -
RS Stock No. 122-8445
Mfr. Part No.51598
HK$2,373.75
Each
units
Liquid Piston - 1 gal/min - 1/4 in 1/4 NPT Female 69bar Brass - - -29°C +148.9°C -
RS Stock No. 122-8437
Mfr. Part No.090-0029
HK$6,919.73
Each
units
Gas, Liquid Piston 0.5 gal/min 20 gal/min - 1/2" 1/2 NPT Female 69bar - - - - +107.2°C -
RS Stock No. 395-6984
Mfr. Part No.166704
HK$407.97
Each
units
Liquid Piston - 3.8 L/min 120 → 240 V ac/dc 1/4 in R 1/4" 10bar Noryl - +100°C - +100°C -
RS Stock No. 849-9394
Mfr. Part No.PFMB7201-C8-A-M
BrandSMC
HK$2,230.25
Each
units
Air, Gas Integrated Display 2 L/min 200 L/min 12 → 24 V dc 8 mm One-Touch Fitting 0.7MPa PBT 0 °C +50°C 0°C +50°C -
RS Stock No. 122-8438
Mfr. Part No.26600
HK$1,803.92
Each
units
Liquid AdjustableShuttle 0.75 gal/min 4 gal/min - - 3/4 NPT Female 27.6bar Bronze - - -29°C +82.2°C -
RS Stock No. 744-0705
Mfr. Part No.PFM725S-C6-A-W
BrandSMC
HK$2,340.00
Each
units
Dry Air, Gas Integrated Display 0.5 L/min 25 L/min 24 V dc 6 mm One-Touch Fitting 750kPa PBT 0 °C +50°C 0°C +50°C -
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