Patent ID: 8104500

Claim:
Liquid level detection apparatus comprising: (a) a vent tube having a first end terminating inside an enclosed pressurized container and a second end terminating in a hollow chamber outside said container; (b) detection means positioned to detect filling noises generated by liquid entering said container and transmitted through said vent tube, said detection means comprising: (i) a check valve positioned to close the second end of said vent tube; (ii) a removable extension tube having an outlet end and an inlet end and adapted to mate with and open said check valve to form a continuous conduit from said first end of said vent tube to said outlet end of said extension tube; and (iii) an acoustic sensor positioned to detect filling noise transmitted through said extension tube; and (c) signaling means responsive to changes in said filling noise transmitted through said vent tube when said first end becomes submerged in liquid.