Patent ID: 7587940

Claim:
A liquid level sensor, comprising: a hollow member having a distal open end adapted to be positioned into a liquid reservoir to a depth below a liquid surface level, the distal open end of the hollow member allowing liquid to enter the tube to an equilibrium level dependent on the volume of liquid in the liquid reservoir; a sensor head unit configured for mounting at a head mount location remote from the liquid reservoir; a connection tubing system adapted to provide a closed fluid conduit between the hollow member at the liquid reservoir and the sensor head unit at the head mount location, such that an air column pressure in said hollow member dependent on said equilibrium level is transmitted to the sensor head unit; said sensor head unit comprising a non-electrically powered system for providing an indication of a position of said liquid surface level, said system including: a bellows member having an input stem portion adapted for connection to the connection tubing system, an expandable body portion and a distal bellows face surface, the bellows body adapted for expansion and contraction in response to differential column pressure changes so that said bellows face surface translates along a range of movement, the bellows member mounted in a sensor head housing with external surfaces of the bellows member exposed to ambient atmospheric pressure; a mechanism responsive to movement of said bellows face surface to provide an indication of a position of said liquid surface level, said mechanism including a sector gear movement including a dial pin, a pinion gear mounted to said dial pin, and a sector gear responsive to said movement of said bellows face surface, said sector gear engaging said pinion gear to rotate said pinion gear and said dial pin in response to said movement of said bellows face surface; and a flow restrictor positioned to dampen instantaneous differential column pressure changes presented to the bellows member while permitting steady state column pressure to be communicated to the bellows member.