Floats and Displacers are simple level measurement devices. They are somewhat identical in their look but they work on different operating principles.
Float level switches work upon the buoyancy Principle according to which “as liquid level changes a (predominately) sealed container will, providing its density is lower than that of the liquid, move correspondingly”. In other words, the buoyancy principle states that “the buoyancy force action on an object is equal to the weight of the liquid volume displaced by the object.”
Displacers operation is based upon the Archimedes Principle which says that “when a body is immersed in a fluid it loses weight equal to that of the fluid displaced. By detection of the apparent weight of the immersed displacer, a level measurement can be inferred.”
Displacers and floats are strictly applied for level detection in case of moderately non-viscous and clean process liquids. They present their best operation in switching applications and over for small periods. One can achieve spans of up to 12m also, but in that case their use happens to be extremely costly.