Operation is based upon simple buoyancy, whereby a spring is loaded with weighted displacers, which are heavier than the liquid. Immersion of the displacers in the liquid results in buoyancy force changing to net force acting on the spring. The spring compresses as the buoyancy force increases.

 A magnetic sleeve is connected to the spring and operates within a non-magnetic barrier tube. Spring movement causes the magnetic sleeve to move into the field of a pivoted magnet, actuating a switch mechanism located outside the barrier tube. Built-in limit stops prevent over stroking of the spring, under level surge conditions.