Abstract: A portable, self-contained leak detection apparatus is provided which is particularly adapted for detecting a relatively small leak in a large fluid storage tank having a fill pipe. The apparatus comprises an air-tight chamber containing a liquid; a slope tube communicating between the liquid in the chamber and the atmosphere, wherein at least a portion of the slope tube extends along the outer surface of the chamber; a source of compressed gas in gaseous communication with the chamber; and a tube for communicating gas between the chamber and the fill pipe of the storage tank.

Abstract: A leak detector includes an air tight chamber having three openings therein. The first opening is connected to a source of compressed air or other gas. The second opening is provided to the fill pipe of a tank to be tested for leaks. The third opening is connected to a slope tube which is calibrated to detect changes in the height of a column of liquid in a slope tube. When pressure is applied to the chamber from the source of compressed air, bubbles are forced into the fill pipe. A corresponding pressure creates and maintains a column of liquid in the slope tube. Changes in the level of the fluid in the tank due to leakage result in a corresponding change in the level of fluid in the slope tube.