The float carries a stainless steel sheathed permanent magnet which rises and falls in the glandless pressure tube with changing liquid level.

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 A switch mechanism is mounted inside the enclosure adjacent to the pressure tube. Switching is achieved with the unique Mobrey ‘three-magnet’ system, giving snap-action ‘latch-on’ switching. 
Vertical movement of the float magnet in the pressure tube simultaneously actuates the secondary and tertiary magnets in the switch mechanism to operate the contacts. This ‘threemagnet’ system enables the float magnet to pass on and actuate switch mechanisms at other levels. Switch mechanisms already actuated cannot re-set until the return of the primary magnet actuates the magnet system once again.