A Comprehensive Guide to Flow Switches - Gn Flow Meter

1. Overview​ ​

A ​ ​thermal flow switch​ ​ is an electronic device used to detect the presence or absence of fluid flow (liquid or gas) based on heat transfer principles. It operates by monitoring the cooling effect of a flowing medium on a heated sensor. When the flow rate exceeds or falls below a preset threshold, the switch triggers an electrical signal for process control, equipment protection, or alarm systems.

Due to its ​ ​no-moving-parts design​ ​, fast response, and high reliability, thermal flow switches are widely used in industries such as HVAC, water treatment, chemical processing, and medical equipment.

​ ​2. Working Principle​ ​

Thermal flow switches operate based on ​ ​heat transfer principles​ ​, primarily using one of two methods:

​ ​(1) Constant Temperature Differential (CTD) Method​ ​

• The device maintains a fixed temperature difference between a ​ ​heated sensor​ ​ and a ​ ​reference sensor​ ​.
• When fluid flows, it carries heat away from the heated sensor, increasing the power required to maintain the temperature.
• The change in power consumption correlates with the flow rate, triggering a switch signal when the flow exceeds or drops below the setpoint.

​ ​(2) Constant Power (Heat Loss) Method​ ​

• A fixed amount of heat is applied to the sensor.
• The temperature drop caused by fluid flow is measured, and the flow rate is determined based on cooling efficiency.
• If the temperature change indicates insufficient flow (e.g., due to blockage or pump failure), the switch activates an output signal.

​ ​3. Caratteristiche principali & Advantages​ ​

​ ​4. Common Applications​ ​

​ ​(1) HVAC Systems​ ​

• Monitors coolant flow in chillers, boilers, and heat exchangers.
• Prevents pump damage due to dry running or low flow.

​ ​(2) Industrial Process Control​ ​

• Ensures proper lubrication in machinery by detecting oil flow.
• Triggers alarms for blocked filters or pipe leaks.

​ ​(3) Water & Wastewater Treatment​ ​

• Detects flow in dosing systems for chemicals or disinfectants.
• Monitors pump efficiency in filtration systems.

​ ​(4) Medical & Laboratory Equipment​ ​

• Safeguards oxygen and anesthetic gas flow in ventilators.
• Ensures consistent liquid flow in dialysis machines.

​ ​(5) Semiconductor Manufacturing​ ​

• Monitors ultra-pure water and gas flow in wafer processing.

​ ​5. Selection Guide​ ​

When choosing a thermal flow switch, consider:
✔ ​ ​Fluid type​ ​ (liquid/gas, viscosity, conductivity)
✔ ​ ​Pipe size & pressure rating​ ​
✔ ​ ​Temperature range​ ​
✔ ​ ​Output type​ ​ (relay, analog, or digital signal)
✔ ​ ​Material compatibility​ ​ (stainless steel, PTFE, etc.)
✔ ​ ​Certifications​ ​ (ATEX, UL, CE for hazardous areas)

Shanghai Cixi Instrument CO.,LTD was founded in 2008 and is located in Shanghai Songjiang industrial park We are the professional flow meter manufacture who integrate R&D, production and sales as one manufacturers. The factory is equipped with advanced production and calibration equipment at home and abroad, ample high-end technical personnel, and a well-established domestic standardized production workshop. It focuses on improving the status of China's flow meter industry in the international arena, and continues to work hard 

Professional production: micro oval gear flow meter, spur gear flow meter, mass flow meter, gear metering pump, valveless piston pump, constant flow pump, vacuum pressure gauge, etc Widely used in water supply, heating, petroleum, chemical, scientific research, environmental protection, paper making, electricity, gas, medicine, food, textile and other fields There is no other manufactures who can produce micro gear flow meter and many company import this kind of flow meter from Japan or America. After we put our micro flow meter into market, the news was spreaded widely and we got many reputation from our client. We now have sold this flow meter to more than 100 countries which contain wide and different applications. Meanwhile our oval gear flow meter has aquired many certificates and filled the vacancy of Chinese market.

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6. Conclusion​ ​

Thermal flow switches offer a ​ ​reliable, maintenance-free solution​ ​ for flow monitoring in diverse industries. Their ability to detect minute flow changes with high accuracy makes them indispensable for ​ ​process safety, energy efficiency, and equipment protection​ ​.

For applications requiring ​ ​fast response, no pressure drop, and long-term stability​ ​, thermal flow switches are often the optimal choice over mechanical alternatives.