The History of Float Switches

The History of Float Switches

Float Switches

A float switch is a device used to detect the level of liquid within a tank. The switch may be used to control a pump or send a signal to an indicator, alarm, controller or other devices.

A search of the patents for float level sensors and float switches will uncover a number of patents dated back to the late 1800’s. One invention references a magnetic float used to induce movement of needles that will give an indication of the liquid level. Like everything else, float switches have progressed much through the years.


Current float level sensors are certainly more sophisticated, reliable and versatile. Today’s float sensors, also known as float switches, float level switches and float level sensors utilize permanent magnets mounted in a float that slides up and down a stem. The float sensor stem contains magnetically activated reed switches that are typically calibrated to the float’s magnetic field. As the float rises or lowers with the tanks liquid level, the float’s magnetic field actuates the internal hermetically sealed, magnetic reed switch. The stem is made of non-magnetic metals or rugged, engineered plastics. When mounted vertically, this basic design provides a consistent accuracy of about ±1/8 inch. Multi-point float switches use a separate reed switch for each level point being monitored.

Side-mounted also known as horizontally mounted magnetic float switches use different actuation methods because of their horizontal attitude. The basic principle, however, is the same: as a direct result of rising or falling liquid, a magnetic field is moved into the proximity of a reed switch, causing its actuation.

Magnetic Float Switch Reliability

The durable construction of these magnetic reed switches ensures long, trouble-free service. When the effects of shock, wear and vibration are minimized, these hermetically reed sealed switches provide precise repeatability and the sensor actuation points remain constant over the life of the float switch. When used properly, these magnetic float switches life span will typically exceed millions of cycles.


Engineers typically choose float style liquid level sensors because they are hyper-reliable, simple, accurate, available with a tremendous amount of mounting methods and other options such as material selection, temperature monitoring and adjustability while being very economical. For more information about how to select a float level sensor for your application, visit our website at

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