Measurement and Control Equipment

Magnetic Flow Switch: Reliable Flow Detection with a Reed Contact

Learn how magnetic flow switches detect flow with a magnet and reed contact in applications from cooling circuits to combi boilers and welding machines, and how to select one.

ORFA Technical TeamUpdated: Oct 30, 20263 min read

Magnetic flow switch with reed contact for flow detection

Many applications need to know reliably whether there is flow: protecting pumps against dry running, preventing heaters from firing without water flow, or stopping laser and welding equipment when cooling water fails. A magnetic flow switch detects fluid movement in a pipe by means of a magnet on a paddle or piston and an external reed contact, switching when the flow rises above or falls below a set value.

What Is a Magnetic Flow Switch?

A magnetic flow switch consists of a paddle, piston or flap moved by the fluid, a magnet attached to it, and a magnetically operated switch (reed contact) in a compartment isolated from the fluid. Because the electrical circuit never touches the fluid, the device is leak-tight and safe.

Working Principle

Paddle movement: When fluid flows, its force moves the paddle or piston.
Magnetic actuation: The magnet on the moving element changes position and actuates the reed contact located in the dry part of the body.
Contact change: The reed contact changes state; a normally open contact closes or a normally closed one opens.
Reset: When the flow stops or drops below the set value, the moving element returns by spring force or gravity and the contact resets.
Signal transmission: The contact status goes to a control system, an alarm circuit or, via a relay, to pump or heater control.

Tip: Reed contacts have a limited switching capacity. Loads such as pump motors or heating elements should be switched through a contactor or relay, not directly through the flow switch.

Advantages

Sensitive detection: Responds to flow changes even at low flow rates.
Electrical circuit isolated from the fluid: The reed contact never touches the medium, reducing leakage and short-circuit risks.
Long life: Magnetic actuation means little contact wear.
Easy installation: Threaded connection directly into the pipeline; on some models the contact function (NO/NC) can be changed by the user.
No power needed for sensing: The contact operates mechanically and magnetically without an external supply.

Selection Criteria

Criterion	Explanation
Switching flow rate	The flow at which the contact changes must suit the minimum safe flow of the process.
Pressure and temperature	Fluid and ambient temperature and line pressure must be within the device limits; ratings depend on the model.
Connection size	Must match pipe size and thread type.
Body material	Brass, stainless steel or plastic, selected for the fluid.
Mounting orientation	Some models are suitable for vertical or horizontal installation only.
Contact type and protection class	NO/NC function and enclosure rating chosen for the application.
Fluid cleanliness	Solids can jam the moving element; fit a strainer upstream if necessary.

Applications

Industrial automation and process cooling circuits
Refrigeration and air-conditioning systems
Water-cooled welding machines and laser equipment
Vacuum coating machines, electric furnaces and polysilicon ingot furnaces
Instantaneous water heaters and combi boilers
Lubrication systems

ORFA’s flow switch range includes models such as the Ensim EFS series and the Ayvaz AK-100 in various connection sizes.

Frequently Asked Questions

Does a magnetic flow switch measure flow rate?

No. It does not measure flow rate; it only detects whether flow is above a set value and switches a contact. Use a flowmeter if a flow value is needed.

Can I run a pump directly from the flow switch?

Reed contacts have a low current rating. Pumps or heaters should always be switched through a contactor or relay.

Can it be used with dirty fluids?

Fluids containing solids or fibres can jam the moving element. Fit a strainer upstream or choose a different sensing method for such fluids.

Conclusion

With a simple design and contacts isolated from the fluid, magnetic flow switches provide reliable flow monitoring in pump, heater and cooling circuits. Choosing the right switching flow, pressure-temperature rating and mounting orientation ensures long service life. Explore flow monitoring products on our Flow Control Equipment page and contact the ORFA technical team for support.

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