A displacer level switch is a type of level sensing device used to detect the level of liquids in a tank or vessel. It operates on the principle of buoyancy, which is the upward force that a fluid exerts on an object that is partially or completely immersed in it. The displacer level switch consists of a weighted probe, called a displacer, which is suspended from a spring and positioned inside the tank or vessel. As the level of the liquid in the tank changes, the buoyancy force acting on the displacer also changes, causing it to move up or down. This movement is detected by the switch, which triggers an electrical signal or a mechanical action, such as opening or closing a valve or turning on a pump. Displacer level switches are highly accurate and reliable, and they are commonly used in applications where the level of liquids must be maintained within certain limits, such as in the oil and gas, chemical processing, and water treatment industries. They can also be used in hazardous environments, as they can be constructed with explosion-proof enclosures and are compatible with a wide range of liquids.