In parts one and two of this ongoing primer on leak testing, we discussed pressure-decay testing and differential pressure-decay testing, respectively. Although those leak-testing methods remain the most widely used, it is often because they are assumed to be the least expensive leak-testing method. To recap: Pressure-decay transducers for leak testing are the least expensive leak-testing sensor technology, often making pressure-decay methods the least expensive route for a given accuracy. However, pressure-decay methods are the slowest methods for leak detection.
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The alternative to pressure-decay test methods are leak-testing systems using mass-flow sensors, which can provide fast and accurate testing over a much wider range of leak/volume ratios and testing conditions at about the same cost as differential pressure systems.
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Leak Testing supply
As I look at these simplified diagrams for the various leak tests, I am concerned about the effect that any leakage through the supply valve would have on the test. It seems that there should be two isolation valves in series with a vent to atmosphere between them. Once the system is pressurized, it would seem logical to close both valves on the supply line and open the vent to atmosphere. This would eliminate any false indications. If there is leakage from the supply side that was nearly identical to the leakage from the unit being tested, the test would indicate zero leakage.
Reply to question.
The schematics were intended to provide a simple, easy to understand illustration of the various technologies. As correctly pointed out, error proofing is essential for all testing applications and should always be implemented in practice.
Posted by QD on behalf of author
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