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Pressure Decay Leak Testing 101

What is Pressure Decay Leak Testing?

Pressure decay leak testing is pressurizing a test part and measuring pressure loss over time. Pressure decay is a preferred technology for most leak testing applications. The best strategy for developing a repeatable pressure decay leak test is to calibrate the test circuit utilizing a calibrated leak or flow standard and a known good part.

 

The most confusing aspect of pressure decay is that we are using a pressure loss to determine a flow rate. Pressure loss units are measured in pounds per square inch or PSI but flow units are measured in standard cubic centimeters per minute or SCCM. This unit conversion is possible thanks to calibration. Keep in mind that pressure decay leak testing is volume dependent. This means that if we calibrate to a basketball we can only test a basketball and not a soccer ball. Think about it this way, we pressurize a tractor tire and a bicycle on different circuits. If each of these tires has the same leak rates, say 5 SCCM, which of these tires will lose pressure more quickly? The bicycle tire has a much smaller volume so the pressure loss will be greater out of the smaller tire. Something else to keep in mind is that anything that changes the pressure in the test circuit will affect the repeatability of the test. All the CTS Test instrumentation is doing is measuring pressure change in the test circuit.

 

What are some common sources of pressure change in a test circuit?

Temperature changes can significantly impact the test results. Think of a milk jug in the sun. What happens? Pressure builds in the milk jug. This is no different for a test circuit when hot parts are tested.

System air pressure fluctuations can affect the repeatability of the test. These pressure fluctuations create unstable conditions in the part and test circuit.

 

To summarize, pressure decay is a volume-dependent test requiring calibration. Anything that affects the pressure of the test circuit will affect the repeatability of the test. Please contact CapEx Sales for more details or additional training about leak test technologies. We provide turnkey leak and functional test solutions and represent Cincinnati Test Systems, the largest leak test company in the world.

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