Patent ID: 7578657

Claim:
An arrangement for controlling the liquid level in a basin by selectively actuating a pump, the arrangement comprising: an environmentally-sealed enclosure, having an internal volume comprising separate first and second chambers and subject to thermal and pressure effects; a barrier fluid, filling a balance of the internal volume, with a first portion thereof contained in the first chamber and a separate second portion thereof contained in the second chamber; a first differential pressure switch positioned in the first chamber, the first differential pressure switch having low and high pressure sides, the low pressure side exposed to the first portion of the barrier fluid and the high pressure side exposed to the second portion of the barrier fluid; and a second differential pressure switch positioned in the second chamber, the second differential pressure switch having low and high pressure sides, the low pressure side exposed to the second portion of the barrier fluid and the high pressure side exposed to the pressure in the basin external to the second chamber.