Patent ID: 7143635

Claim:
A method for detecting fuel leaks from an underground fuel storage tank comprising the steps of: (a) lowering a reference tube into said underground fuel storage tank through an access port within said underground fuel storage tank to test for said fuel leaks, wherein said reference tube includes a seal housing positioned at a lower end of said reference tube, and a length that is at least the diameter of said underground fuel storage tank being tested for said fuel leaks; (b) providing a seal affixed to the bottom end of said seal housing in slidable engagement with said reference tube, wherein said seal is normally held in an open position; (c) allowing fuel within said underground fuel storage tank to enter said reference tube as said operator lowers said reference tube into said underground fuel storage tank; (d) closing said seal when said reference tube engages the bottom of said underground fuel storage tank to prevent said fuel within said reference tube from exiting said reference tube; (e) measuring a pressure differential between said fuel within said reference tube and said fuel external to said reference tube which is stored within said underground fuel storage tank, wherein a differential pressure transducer mounted on said seal housing measures said pressure differential; (f) generating an analog electrical signal containing pressure differential data which is indicative of said pressure differential measured by said differential pressure transducer, wherein said differential pressure transducer generates said analog electrical signal; and (g) processing said pressure differential data to determine a leakage rate of said fuel from said underground fuel storage tank, wherein said method measures said fuel leaking from said underground fuel storage tank at said leakage rate of 0.067 gallons per hour with a probability of detection of ninety five percent.