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Leak Testing Methodologies

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PRESSURE DECAY



If we consider a component charged at a given

pressure, any possible leak can be associated with a

decrease of internal pressure. Therefore, if a

component needs to be leak tested, it can be first

charged (usually with dry air or nitrogen) at a set

pressure and then its pressure can be monitored for a

set amount of time. A pressure decay indicates the

presence of a leak.

This system is simple, compact and easy to use. It is

cheap, dry and it does not require an operator’s

judgement for its use.

The leak detection sensitivity depends on the volume of the unit to be tested (the

bigger, the more it takes to stabiles the internal pressure before monitoring it), the

pressure transducer resolution and testing time.

Moreover it presents the following disadvantages:

- low sensitivity (down to 10-2 mbar·litre/sec)

- requires long times to stabilise the pressure level before this is monitored over

time

- very susceptible to environment changes (particularly temperature)

- susceptible to mechanical instability (when pressurising the component its

volume can change, therefore the results can be misleading)

- guarding is required for high pressures

- the leak cannot be located

- low throughput, especially for large components



This method can represent a good preliminary leak test to detect gross leaks before

a final automated fine leak test is carried out using helium (if a component has a

gross leak and this is not detected first with a pressure decay test, large quantities of

helium will leak out of the test unit, contaminating the system and making it

inoperable for a long time).

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