|External Cage Operating Principle External Cage Cut Away
All float operated liquid level controls operate on the basic buoyancy principle, which states, "a body (float) immersed in a liquid is buoyed upward by a force equal to the weight of the displaced liquid". As a result, floats follow the liquid surface and move a distance equal to the liquid level movement. Because of this, they are normally used for narrow level differential applications such as high-level alarm or low- level alarm.
External cage float type level switch controls use a float and magnetic coupling action that causes switch operation for fluid level measurement.
Liquid level movement changes the buoyancy force on a displacer suspended from a range spring. The force change on the spring causes it to extend or compress, moving an attraction sleeve into or out of the field of the switch magnet, actuating the switch.