Thermal dispersion flow switch is also called as thermal flow switch or thermal difference flow switch.Thermal dispersion flow switch belongs to a kind of  digital electronic flow switch.It has no moving parts, so it features long life,higher accuracy,stable performance,wide flow range,wide pipe size,wide medium application of water,oil and air. We aim to develop and supply thermal flow switch with lower price.

Thermal flow switch is developed on basis of thermal diffusion technology. The value of thermal diffusion that is calculated by 2 heat resistors is used to measure flow rate of water,oil or air. When the flow rate is over the settable value,the flow switch will produce signal to relay,then relay to control ON/OFF of flow.Thermal flow switch has other terms:digital flow switch, thermal flow indicator,thermal flow controller,etc. The default output is LED status indication for flow range,but LCD display window can be provided. It is ideal solution for you to replace existing mechanical flow switch.

Our thermal flow switch adopts fully enclosed design which can ensure water-proof and damp-proof. Its probe is specially processed and solve the problem of probe corrosion and scaling while under poor quality water. Thermal flow switch is no maintenance after setting and no need to do adjusting often.So it is a kind of wide-using flow switch and can be widely used for pipe flow control in industries of petroleum, chemical, electric power, water treatment, metallurgy, paper making, ship and boiler, etc.


Thermal flow switch is designed on the principle of thermal diffusion.Thermal diffusion technology is a kind of reliable technology,even though under harsh environments.Its typical sensing parts include two thermal resistors. When the two resistors are put in fluid, and one is heated,the other is used to sense medium temperature. The temperature difference of two resistors is relative with medium flow and medium character. When heating power is permanent,temperature difference has a functional relationship with flow rate. Electrical wiring module can get flow rate by checking the temperature difference between the two resistors.Then the module outputs 4-20mA or control relay.Meanwhile, LED light can indicate current flow rate.

Technical Features:

  • No moving parts
  • No maintenance
  • Digital Display(Part of models),LED flow indication,convenient for view
  • Dual-adjusting, more accurate
  • Integrated design,compact size,
  • Water-proof design,easy to install
  • Alarm points adjustment
  • Special processing probe, anti-corrosion and anti-scaling
  • Wide pipe size,wide flow range


Technical Specification:

  • Flow setting range:1-150cm/s(water);3-300cm/s(oil);20-2000cm/s(air).
  • Power supply: 24V+/-20%DC or 230VAC+/-10%(Indicate while order)
  • Signal output: PNP,NPN,Relay; Normal open+Normal close
  • Current:Max 400mA(NPN or PNP); Max 4A(relay)
  • Empty load current:Max 80mA
  • Flow indication: 6pieces LED
  • Setting way: Potentiometer setting
  • Pressure range: 100bar
  • Medium temperature changing:<=4 deg.C./second
  • Response time:1-13S,typical:2S
  • Initializing time: about 8S
  • Electrical protection:protection for reverse,short circuit,overload
  • Protection class: IP67
  • Medium temperature:-20 to 80 Deg.C.
  • Environment temperature: -20 to 80 Deg.C.
  • Storing temperature: -20 to 80 Deg.C.
  • Wring way: M12 socket connectors
  • Weight:about 0.4kg
  • Probe Material: stainless steel; Probe length can be made as requirement.
  • Electronic enclosure: PBT or Stainless steel
  • Connection wire: 2m.(Longer optional)
  • Connection Ways: thread (Can be made to meet different standard)

Installing way:  insertion and inline type

Outputs Wiring Diagram

Note: Please be cautious that voltage-overstress, current-overstress,wrong wiring,etc will damage the flow switches.  


  • For liquid/air,widely for pneumatic and hydraulic pressure system.
  • Can be used for water flow monitoring ,coolant and lubricating oil; and protection of empty pump running.
  • Fire extinguisher system...

Diagram of Fire Sprinkler Flow Switch System

Application Case

Fire Alarm

Fire Sprinkler

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