How Magnetic Float Level Switches Work

Magnetic Float Switch Working Principle

The working principle behind magnetic float level switches is to utilize a magnetic field to open or close a circuit as the level of a liquid within the chamber rises or falls. The stainless steel float within operates on the basic buoyancy principle that the force on a buoyant object is equal to the mass of liquid displaced by the object. Partially submerged within the liquid surface, the float moves within the chamber when the liquid level moves, thereby accurately tracking the liquid surface motion.

Utilizing magnetic fields to open and close switch points in many float level switches is common and used in many industries. It’s a simple, smart technique for level measurement and maintenance. As the float moves with the liquid level, it moves a magnetic sleeve into or out of the field of a magnet that actuates a switch, causing switch operation. A non-magnetic barrier tube effectively isolates the switch mechanisms from the controlled liquid.

Magnetic Liquid Level Switch

A magnetic liquid level switch consists of two main components: a magnet embedded inside a float, and a reed switch placed in an enclosure. The single unit or multiple reed switch units are housed tightly in a stainless steel or an engineering plastic stem and a permanent magnet is sealed inside a float whose rise and fall causes the opening or closing of a mechanical switch, either through direct contact or in proximity of a reed switch due to the magnetic field.

It may not be too hard to imagine a magnet placed inside a float, nor does the concept of harnessing magnetic fields to work in liquid level switches. However, it’s a little harder to understand a reed switch. A reed switch consists of two ferromagnetic contact tips called, ‘reeds,’ that are encased in a glass tube. As the magnet passes by the contacts in the encased reed switch, they are drawn or touch and complete a signal circuit between the two lead wires.

How It Works

The float rides on the process liquid surface, precisely tracking liquid surface motion. Rising liquid level lifts the float, sliding the attraction sleeve up inside the enclosing tube and into the magnetic field to actuate the electrical or pneumatic switch. This signals the presence of liquid.

Subsequently, falling liquid level lowers the float, drawing the attraction sleeve out of the magnetic field to deactivate the electrical or pneumatic switch. This signals the absence of liquid. Magnetic float level switches are generally able to handle high-temperature applications, and sometimes prove useful for close interface detection.

By using a permanent magnetic float level switch and reed contact the switching operation is non-contact, free from wear and needs no power supply. All functioning of the magnetic float switch is fully independent of vibrations, bubble formations, foaming, conductivity, and harmful vapors.


Magnetic float level switches can provide level measurement for almost all liquid media. Properly used, float switches can deliver millions of on/off cycles, for years of dependable operation. They are ideal for narrow level differential applications such as high or low level alarms and controls in power plants.

You’ll find them anywhere there is pump and level control, i.e., wherever liquid flows in and out of tanks, pressure vessels, or sumps:

  • Chemical industry
  • Petrochemical industry
  • Natural gas
  • Offshore
  • Shipbuilding
  • Machine building
  • Power generating equipment
  • Power stations
  • Process water and drinking water treatment
  • Locomotive & railroad equipment
  • Off highway vehicles
  • Bulk storage terminals
  • Textile, pulp & paper industries
  • Food, beverage, & dairy industries
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