What is a Level Switch?

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  • Written By: Shannon Kietzman
  • Edited By: Niki Foster
  • Last Modified Date: 17 September 2017
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A level switch, also commonly referred to as a float switch, is a device that senses the level of a liquid in a water tank. It is a specialized type of pressure switch, which is capable of sensing pressure with a plastic tube. In a washtub, for example, the plastic tube runs from the level switch within the control console and continues down the outside of the tub’s bottom.

The plastic tube in a level switch is filled with air. In the example of the tub, the water enters the inside of the tub, and some of it gets into the plastic tube. The water in the plastic tube then climbs and places pressure on the air inside. In turn, this causes the air pressure to increase. Ultimately, the air pressure reaches a point at which it triggers the switch.

A level switch is usually available in both small and large sizes. In addition, these devices can range from simple to very intricate designs. The simplest form of level switch involves a mercury switch located inside a hinged float. A more complicated model utilizes complex sensors.

In general, these switches are adjustable. It is also possible to purchase a two-stage level switch. This can be quite handy because it can prevent flooding.


With a two-stage level switch, the liquid within an object rises up to the trigger point at the first stage. After a pump is activated, the liquid will continue to rise if the pump is blocked or if it fails to operate correctly. In this case, the second stage of the switch goes into effect, turning the pump off, setting off an alarm, or both.

A level switch can also be versatile enough to detect wet and dry conditions. In addition, it can detect liquid to liquid interfaces and can determine whether a substance is foam, air, or liquid.


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