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.
You can download the application note by joining Uson’s
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it’s free to join and registered users can access all our application notes,
white papers and product literature.