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庫存編號 256-578
HK$453.86
單位
Liquid Control Valve 3 L/min 6 L/min 240 V ac 22 mm - 10bar - +5 °C +85°C +5°C +70°C -
RS庫存編號 395-7230
製造零件編號020-3497
HK$2,395.30
單位
Liquid Paddle 15 L/min 125 L/min 250 V 1 in 1 BSP 55bar Brass - - -18°C +100°C -
RS庫存編號 395-6962
製造零件編號166702
HK$309.05
單位
Liquid Piston - 1 L/min 120 → 240 V ac/dc 1/4 in 1/4 BSP 10bar Noryl - +100°C - +100°C -
RS庫存編號 256-562
HK$380.00
單位
Liquid Control Valve 3 L/min 6 L/min 240 V ac 15 mm - 8bar - +5 °C +85°C +5°C +70°C -
RS庫存編號 613-4238
BrandRS PRO
HK$1,269.06
單位
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庫存編號 744-0913
製造零件編號PFM710S-C4-A-W
BrandSMC
HK$2,340.00
單位
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庫存編號 906-7746
製造零件編號V8
HK$644.08
單位
Gas, Liquid Vane Operated 10.8 (Liquid) gal/min, 39 (Gas) gal/min 45 (Liquid) gal/min, 168.6 (Gas) gal/min 120/250 V ac 1 → 6 in 1 NPT Male 10.34bar Polyphenylene - - - +100°C 5 A
RS庫存編號 395-7016
製造零件編號166703-A
HK$318.75
單位
Gas Piston - 158 L/min 120 → 240 V ac/dc 1/4 in 1/4 BSP 10bar Noryl - +100°C - +100°C -
RS庫存編號 395-7218
製造零件編號020-3490
HK$2,194.33
單位
Liquid Shuttle 19 L/min 57 L/min 250 V 1 in 1 BSP 27bar Bronze - - -20°C +80°C -
RS庫存編號 906-7734
製造零件編號V4-2-U
HK$3,042.36
單位
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庫存編號 395-7202
製造零件編號020-3491
HK$2,438.14
單位
Liquid Shuttle 7.5 L/min 30 L/min 250 V 1 in 1 BSP 27bar Bronze - - -20°C +80°C -
RS庫存編號 395-6940
製造零件編號166701
HK$357.50
單位
Liquid Piston - 0.2 L/min 120 → 240 V ac/dc 1/4 in 1/4 BSP 10bar Noryl - +100°C - +100°C -
RS庫存編號 780-0125
製造零件編號LFS-04
BrandCynergy3
HK$1,868.18
單位
- Paddle 15.2 L/min, 19 L/min 60.6 L/min, 83.3 L/min 230 V 1 → 3 in 3/4 BSP 20bar Aluminium Alloy - - -30°C +150°C 1 A
RS庫存編號 906-7743
製造零件編號V4-SS-2-U
HK$4,387.01
單位
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 138bar Stainless Steel -20 °C +73°C -20°C +73°C 10 A
RS庫存編號 395-7173
製造零件編號020-0315
HK$1,332.53
單位
Liquid Piston 0 L/min 55 L/min 220 V 3/8 in 3/8 BSP 0.3bar Brass - - - +90°C -
RS庫存編號 613-4244
BrandRS PRO
HK$1,429.69
單位
Gas, Liquid Paddle 14 L/min 18 L/min 250 V ac 25 mm 1 BSP Female 25bar Nickel Plated Brass - +110°C - +110°C 5 A
RS庫存編號 395-7195
製造零件編號020-3489
HK$2,212.47
單位
Liquid Shuttle 3 L/min 22.5 L/min 250 V 1 in 1 BSP 27bar Bronze - - -20°C +80°C -
RS庫存編號 849-9398
製造零件編號PFM711-N02L-A-A
BrandSMC
HK$2,491.59
單位
Dry Air, Gas Integrated Display 2 L/min 100 L/min 24 V dc 1/4 in NPT 1MPa PBT 0 °C +50°C 0°C +50°C -
RS庫存編號 122-8441
製造零件編號51582
HK$2,373.75
單位
Liquid Piston - 0.1 gal/min - 1/4 in 1/4 NPT Female 69bar Brass - - -29°C +148.9°C -
RS庫存編號 613-4216
BrandRS PRO
HK$1,213.93
單位
Gas, Liquid Paddle 4 L/min 5.5 L/min 250 V ac 10 mm 3/8 BSP Female 25bar Nickel Plated Brass - +110°C - +110°C 5 A