Immersion leak testing or "dunk testing" is still a popular method of leak detection and it's effective in certain situations. However, it has one massive disadvantage - its very difficult to quantify a leak rate by observing bubbles.

Sometimes we run across somebody who has been dunk tank testing and has a leak specification defined as “x bubbles per minute”. Certainly this is one way to subjectively compare leaks, but it is far from the most accurate and reliable.  What size are the bubbles? What if they were not counted correctly? Add to that the problem of drying parts, possible future corrosion or damage, disposal of contaminated water and the hazard of slipping on spilled water and it’s clear that dunk testing has very limited appeal in today’s modern manufacturing industry.

Pressure decay leak testers use a pressure sensor to measure a  change in pressure and the process of converting that pressure change to quantify a leak rate is not always straightforward. Users need  to know the volume of the part and then, if possible, program that value into the leak tester so that the instrument can perform the calculation to convert pressure change over time to a volumetric leak rate.

One way around the procedure is to use a mass flow tester – volume is not important to this type of tester, it simply displays a flow rate in the user’s selected engineering units.

Uson’s application note  Quantified Leak Rate Using Mass Flow AN-9 describes how the Sprint iQ leak tester can be used in this manner. Other models such as Qualitek mR, Optima vT and Vector can also perform the mass flow test described.

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