Bubble tightness is a wide terminology which simply means zero leakage when the valve is in close position.Now if theSlurry pumps medium is water then the valve should have zero leakage at twice the rated pressure if the testing is based on AWWA Standard.i.e If the line pressure is 10 bars then the Other pumpsvalve should be bubble tight at 20 bars at closed position for 10 minutes,This test is also known as seat test in the case of Rubber seated butterfly valves.The method is :- The Butterfly valve is Gate Valvesmounted on a test flange or spool piece where the hydrostatic pressure is built up to the test pressure at closed position.The other end of the valve is thoroughly cleaned with Check Valvescompressed air so that the disc and the seal is free from dust and watery compounds;This is done because Ball Valvesyou have to visually see the contact area properly.Now,The contact area of the disc and seal should not have any leakage or drop in pressure which can be verified by a pressure gauge(Even a delayed sweating is not permitted).This test is done for the time based on the standard you apply for the test procedure. I would be glad to know from the members the procedure applied if the media is other than water and for valves other than Butterfly valves.

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