The pressure rise test - At least better than the bubble test

In my last article "Have you seen the bubble? - The disadvantages of bubble leak testing" I took a closer look at the bubble test in a water bath.??Today, I turn my attention to the pressure rise test. I rarely see this method in industrial leak testing, but here and there I still come across it.

A brief explanation of how it works

The pressure rise test, also known as "vacuum pressure testing", can be found, as the name suggests, mainly in vacuum systems.?The test specimen is connected to the vacuum system via a port and evacuated. During a predefined period of time, the possible pressure increase in the test object is now observed. If the pressure rises above the defined value, a leakage can be assumed.

Theoretical leakage rate vs. realistic leakage rate

In theory, i.e. under laboratory conditions, a leakage rate of up to 10-4 mbar l/s can be detected with this method. Under realistic conditions, in a production environment, it has been shown that a leak rate of 10-3 is more realistic. That's a full decade between "tight" and "leaky."

For the math specialists among us, the formula for determining the leak rate is briefly shown here:

Volume * Pressure Rise / Measurement Time

Limiting factors for the pressure rise test

Have you ever tried to evacuate a chip bag? Sure, the chips end up in the belly but the bag is still filled with air. When we start to evacuate this air through the mouth, the bag contracts and changes its shape.

This example can be adapted to many components that are made of plastic, for example, and have a low stiffness.

The volume is also a decisive factor why this test method is not applicable for all test parts.

Overpressure and vacuum, does that go together?

No! 90% of the components are subjected to overpressure during use. It is always advisable to choose a test method that corresponds to the application of the object.

To make it a bit clearer, let's imagine a wiper water tank. We want the contents to stay in the tank and not leak out uncontrollably, so why choose a test method that reflects exactly the opposite case.??Something does not necessarily have to come in if something comes out.

This way the leakages we are looking for remain undetected!

For this application, the pressure dekay test is more suitable.

Are there also advantages?

Although the disadvantages outweigh the advantages, there is also a serious advantage to be noted, the independence from temperature. Since there is a vacuum in the test object, there is no volume of gas that influences the temperature.

An advantage rarely comes alone, usually a disadvantage comes along, in this case it is the limited pressure difference. This is limited to 1 bar due to the atmosphere.

Summary

Each method has its advantages and disadvantages, in this case the disadvantages such as the limited pressure difference and the dependence on material and stiffness of the object to be tested outweigh the advantages.

So if you should test a thin-walled plastic tank for leaks with the pressure rise method, we should talk!

Next week I will take a closer look to the very popular pressure dekay methode, so stay tuned!

If you have further questions so far, please drop me a message.

Yours

Ben