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Liquid level switches use the movement of a float to open and close circuits in a liquid system. They can be mounted vertically or horizontally within the system, either immersed in the liquid or outside of it. Due to the nature of the float, the switches will activate when the level of the liquid reaches a certain point. For liquid level switches that are placed above the general level of the liquid, this means that the liquid will need to rise before the switch is activated. Immersed switches are often activated by a drop in liquid.

In a liquid level switch, a permanent magnet is typically attached to the float. As the liquid level changes, the position of the float also changes, altering the position of the magnet. In some cases, the position shift of the magnet may actuate an electric circuit; in pneumatic systems, it may result in air moving through a different output valve. According to the design of the switch, a change in liquid level will typically cause the switch to allow or cease flow of liquid to the system. It may also be designed to trigger other systems, or relayed to various process controllers and data loggers.

A wide range of materials are used in liquid level switches, including polypropylene, polysulfone and other synthetics. Various metals are used in the switch’s wire leads, fittings and magnetic interface. Uses for these switches include a number of domestic appliances and automobile components, as well as certain food processing applications. They can be used to detect level changes in virtually any liquid, including water, oil and processing chemicals.

Although liquid level switches are reliable and relatively inexpensive, other, more accurate technologies are available, such as ultrasonic sensors and various electrical devices. Changes in system pressure and liquid consistency can affect the performance of a liquid level switch, and volatile or complex applications may require alternative detection and control mechanisms.