In industrial systems, flow monitoring is essential for protecting pumps, cooling circuits, hydraulic systems, lubrication lines and process equipment. When flow stops or drops below the required level, equipment damage, overheating, production loss or process instability may occur.
The EFS 81 Thermal Flow Switch is designed to provide reliable flow detection for both liquid and gas applications. With its thermal measurement principle, stainless steel wetted parts, adjustable set point and no-moving-part design, EFS 81 offers a practical and stable solution for industrial flow monitoring.
What Is EFS 81?
EFS 81 is a thermal flow switch used to detect flow presence and flow changes in pipelines. It is suitable for gas and liquid applications and can be used in hydraulic pressure systems, circulating water systems, cutting fluid monitoring and lubricant monitoring.
The product is designed with precision electronic components and a stable circuit structure. According to the catalog, this supports accurate and reliable flow signal output in demanding industrial applications such as iron and steel, metallurgy, pharmaceutical and chemical industries.
Thermal Measurement Principle
EFS 81 operates based on the heat exchange principle. The probe contains a heating module and a thermal sensing module.
When there is no medium flow in the pipe, the thermal circuit receives a fixed value. When fluid flows across the probe, heat dissipation changes depending on the medium velocity. The thermal circuit detects the temperature difference between the heating module and thermal module and converts this change into an electrical signal.
The processor then converts this signal into PNP, NPN or relay output, depending on the selected configuration.
Suitable for Liquids and Gases
One of the main advantages of EFS 81 is its dual-use capability for gas and liquid media. It can be used in water, air and oil applications.
The measurement ranges are 0.3–3 m/s for water, 2–3 m/s for air and 0.3–3 m/s for oil. This makes it suitable for many industrial flow monitoring points where simple flow/no-flow detection is required.
No Moving Parts
EFS 81 has no moving parts. This reduces mechanical wear and minimizes maintenance requirements compared with mechanical flow switches.
In applications involving water, oil, air or process fluids, the absence of moving parts helps improve long-term reliability and reduces the risk of jamming caused by contamination or deposits.
Adjustable Set Point
The flow set point can be adjusted with a potentiometer. This allows users to define the switching point according to the required flow condition of the application.
The adjustable set point makes EFS 81 suitable for different pipe sizes, process conditions and media types. It also provides flexibility during commissioning and maintenance.
LED Display and Local Status Indication
EFS 81 includes an LED display for local indication. The front view shown in the catalog includes display, contact and LED information.
This visual feedback helps operators and maintenance personnel check switching status directly at the installation point, making troubleshooting and commissioning easier.
Technical Specifications
EFS 81 offers an accuracy of ±1% and ±0.1 m/s. The setting time is 3 minutes, and the response time is 2 seconds, adjustable within 2–10 seconds.
The maximum working pressure is 100 bar, and the ambient temperature range is -20 °C to +80 °C. The maximum medium temperature change gradient is 300 K/min.
The housing material is PVC, while wetted parts are 316 stainless steel. This provides good durability for industrial liquid and gas applications.
Outputs and Electrical Ratings
EFS 81 supports several output options. Standard output includes PNP NO/NC, while relay NO/NC and optional NPN NO/NC outputs are also available.
For relay output, the contact rating is 5 A / 250 VAC / 30 VDC. For PNP or NPN output, the maximum current is 250 mA.
The standard power supply is 24 VDC, with 220 VAC available as an option. Current consumption is less than 60 mA.
Electrical Connection and Protection
The electrical connection is made through an M12 socket. The device includes output protection against reverse polarity, short circuit and overload.
The protection class is IP67, making EFS 81 suitable for industrial field environments where dust, moisture or splashing may be present.
Mechanical Design and Installation
The standard connection is M18 x 1.5 mm female, with other connection options such as 1/4" BSP male thread and 1/2" BSP male thread listed in the ordering structure.
The standard stem length is 45 mm. The catalog drawing shows compact dimensions, including an 80 mm body length, 50.5 mm body width and 78.3 mm height.
The mounting diagram highlights the importance of correct installation distance from bends or disturbances. A straight pipe distance of a > 3D is shown to support stable measurement conditions.
Application Areas
EFS 81 can be used in hydraulic pressure systems, circulating water systems, cutting fluid monitoring, lubricant monitoring, cooling circuits and general industrial flow monitoring applications.
Typical industries include iron and steel, metallurgy, pharmaceutical, chemical, machinery and process industries.
It is especially useful for protecting equipment where minimum flow must be confirmed before operation continues.
Advantages of EFS 81
The EFS 81 offers several practical advantages for industrial users. It has a clear LED display, stainless steel wetted parts, no moving parts, easy assembly, adjustable set point and low pressure drop.
These advantages make it suitable for applications requiring reliable flow/no-flow detection with minimum maintenance and simple installation.
Why Choose EFS 81?
EFS 81 is a strong choice when an application requires stable electronic flow monitoring for both liquids and gases. Its thermal measurement principle provides reliable detection without mechanical moving parts.
With adjustable switching point, PNP/NPN/relay output options, IP67 protection, 100 bar pressure capability and 316 stainless steel wetted parts, EFS 81 can be integrated into many industrial systems.
For pump protection, cooling system monitoring, lubrication supervision and process safety, EFS 81 provides a compact and dependable flow switch solution.
Conclusion
The EFS 81 Thermal Flow Switch is a reliable electronic flow monitoring device for liquid and gas applications. Based on the thermal heat exchange principle, it detects flow changes and converts them into PNP, NPN or relay output signals.
With no moving parts, adjustable set point, LED display, 316 stainless steel wetted parts, IP67 protection and measurement ranges for water, air and oil, EFS 81 is well suited for industrial flow monitoring in hydraulic systems, circulating water lines, cutting fluid circuits and lubrication applications.