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The Problem – Leak Testing If you manufacture valve body castings, how can you quickly test it for leaks? A traditional pressure decay test may take several minutes to an hour, depending on the leak rate you expect to measure. How can this process be accelerated to allow for faster production times?
The Solution A differential pressure leak test is used instead of a pressure decay test. In this type of test, two identical valve bodies are pumped up to the same pressure using air. One of the two items is known not to leak. An equalizing valve and a differential pressure transducer are plumbed between to the two valve bodies. When the test pressure is reached, the equalizing valve is closed. The differential pressure transducer has a full scale of just a few inches of water, even when the static pressure during the test is several hundred psig. If any leakage occurs in the item under test, a small pressure difference will develop and this will be immediately sensed by the differential pressure transducer. The differential pressure leak test takes advantage of the ability of the transducer to sense very low differential pressures, even when the static pressure is quite high. In the traditional pressure decay test, it may take some time for the pressure in the item to decline sufficiently to register on a transducer that must accommodate the full test pressure within its range. In addition, as air is compressed in the item during the pumping phase of the test, adiabatic heat is generated. This heat can increase the pressure inside the device under test once the air pump has stopped. The increase in pressure, although slight, can mask small leak rates in a pressure decay test. Because two identical items are charged with air at the same pressure (and over the same timeframe) in the differential test method, adiabatic heat affects the pressure in both items equally, and the only cause for a change in differential pressure is leakage from the device under test.
Validyne Products The Validyne P55 is used extensively in leak testing because it is available in differential pressure ranges as low as 0.1 psid while accepting static test pressures of up to 3200 psig.
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| Phone: 818.886.2057 || Email: Sales@validyne.com |
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