The Model 2000A Kuhlman Instrument has the reservoir extended above the fluid, with a small tube extended from the top of the reservoir down into the fluid. When pressure is applied to the instrument, then reading the amount of pressure on the scale (016 inches of water) or (0150 lbs. PSI), if a large leak exists the fluid will drop rapidly in the instrument tube. If a fine leak exists, you can observe this by slowly closing Valve #1, this will force fluid up the small tube inside the reservoir... MAXIMUM WORKING PRESSURE IS 150 PSI Advantages The saving in time and man hours on the job. The Model 2000A instrument will show a leak almost instantly , so that it can be repaired at once (no one has to wait for a long period of time determining if a leak exists). Primary Function... This instrument can be used when an exact reading of pressure is not necessary, but leak detection is. DESIGNED FOR... Gas Utility Servicemen, Plumbers servicing gas operated products, Contractors, Pipeline installations, Tank and Storage installation, and Industrial uses. The Kuhlman Instrument has been specifically designed for the person who wishes to leak detect from (016 inches of water) or (0150 lbs. PSI).