Top Mounted Level Switch work on permanent Magnet Reedswitch basis. The floats which contain permanent Magnets move freely between their stops rising or falling with Liquid level movement. Hermetically Sealed within the tube are reed switches, Completed isolated from the medium. The Magnet's field actuated the reed switch as the float moves while the Stoppers restrict overrun and prevent the reed switch returning to its original position. Stopper positions should not be changed.