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Guide to leak testing

The Industrial Physics FAQ guide to leak testing

Does your packaging ensure that your products won’t leak out of their enclosed space? While giving you the confidence that no unwanted environmental contaminants can enter.

Is there potential that the products you’ve manufactured have holes, cracks, or flaws that have been missed throughout your quality process?

The answers to these fundamental questions can be found through product and package leak testing.

There are several leak test methods. Do you know your pressure decay test from your mass flow leak testing? Perhaps you’d like to know the calculation used to work out a leak rate?

Industrial Physics is a designer and manufacturer of the best leak test solution technology. In this useful guide we touch on aspects of the leak test principle and explore some of the frequently asked questions on leak testing.

The things leak tests check for

To put it bluntly, a leak test tests for leaks. And it’s achieved with a leak tester!

Before we go any further…it’s sensible to define what we are testing for, when we carry out a leak test.

Before exploring leak test methods…how do you define a leak? Well, in the packaging world, a leak is a hole or a path through which the package contents may escape. Or through which environment contaminants may enter.

The process of quantifying a product leak is called leak testing. You’ll also find it referred to as package or seal integrity testing in the pharmaceutical, medical and food industries.

Depending on how far you zoom in, you’ll find holes in everything. And it’s up to you as a packaging manufacturer to define acceptable limits regarding a leak test failure.

But it’s not only used for packaging. Leak testing can be applied to all types of products made across sectors as diverse as automotive to aerospace and from healthcare to heavy industry. Whenever you need to know if your products contain any unwanted defects- you’ll find a leak test method to do the job.

When you have defined an acceptable point of failure, you can decide upon the right type of leak testing for your organization.

The definition of the leak rate

Everything leaks over time. So, it’s a good thing that leak testers were invented!

When it comes to product and packaging leak testing the key question to bear in mind is ‘how much leakage is too much leakage?’ And to know up-front the standards or specifications that you’re working towards for your products to be accepted.

Simply speaking, to understand leakage and the leak test principle you must get familiar with a basic relationship:

∆VLeakage (or Leak Rate) = ∆V (over) ∆t

(where ‘V’ is the volume of the medium exiting or entering and ‘t’ is the time period you’re measuring the change in volume).

To break the leak test formulae down in packaging terms. Take your sealed package; work out how much air or fluid escapes in a predetermined amount of time; then show it as measurement, such as cc/min, cc/sec, or ft3/hr.

Pressure decay leak test

Do you need to ensure the quality of your package or product? A pressure decay leak test offers the results you require.

With this type of leak test the part being examined is pressurized. Meaning it’s filled with air until it reaches a set pressure. It’s then isolated from the supply pressure. Using a pressure sensor you then monitor the build up within the part; as the air leaks out, the pressure drops. Next up you calculate the change in pressure over a certain period of time, which gives you: the leak rate.

It’s a solid method of generating quantitative information. Hard data points can be recorded and you get tangible intelligence for reliable decision making.

This type of package leak test isn’t labor intensive as you become less reliant on the operator. Use it to determine an ‘accept to reject’ criteria that works for your business.

Taking a volumetric or mass measurement approach is best for defining leakage in a test system. But the pressure decay leak test is an easy and fast method, most helpful when you simply want to identify a ‘good’ or ‘bad’ part.

Your pressure decay testing process is as sensitive as the time available for the test. And we’re not kidding when we say it’s fast: under specific conditions, two to four second cycles are achievable!

One final point. Vacuum testing can also be achieved with a pressure decay test. As a ‘vacuum’ merely represents a pressure below atmospheric conditions.

Mass flow testing

Mass flow leak testing is similar…with a slightly different approach. Mass flow testing uses the intrinsic properties of air to directly measure the amount of it escaping a closed system.

Through this type of leak test – once again, the test part is pressurized, but you keep it connected to the supply pressure. On reaching an equilibrium – when the pressure in the part is stabilized – you’ll know that the gas flowing in from the supply is equal to the total leakage of gas flowing out.

Mass flow leak testing sensors have limited low range sensitivity; they’re generally used for readings greater than one sccm (0.02 sccs). A pressure regulator establishes the testing pressure, and then the sensor records any movement of air out of the test system. Through this leak test the leak rate is measured directly – therefore no conversion is necessary. Another benefit is that the mass flow leak testing is not dependent on temperature change, removing a layer of complexity associated with the pressure decay test.

So now you understand a little about this leak test principle and can see how mass flow leak testing is used to measure air escaping from a closed system. But did you know that it can also identify obstructions too? Read on…

Occlusion leak testing

If you manufacture products for a healthcare setting – such as medical catheters or IV sets. Or if you work with check valves and tubing – the occlusion leak test is super important.

An occlusion leak test will tell you if air or liquid is flowing as intended through the item. If it is – then the object’s passages are clear. If it’s not, then it’s likely you have a blockage – also known as an occlusion.

To put it simply. An occlusion leak test works by trapping pressure inside your product and then measuring the release against an expected pressure loss. This pressure leak test begins straight after ‘the fill stage’ – as soon as you obtain the desired pressure. As the air or liquid leaves through the downstream port, it’s carefully measured. Then you compare the leak test results against your expected pressure decay for that item to determine whether it’s a pass or a fail.

As we touched on in the answer to FAQ 4, mass flow leak testing can be used to check for product blockages. You can find out how – and read about other pressure leak testing methods, including back pressure occlusion leak testing and the pressure drop occlusion leak test here.

Leak testing expert help

We trust that our FAQ guide has helped to plug any few gaps in your leak testing knowledge. But if you have any less frequently asked questions about the process. Or if you’d like to talk through the many styles and models of packaging leak testing equipment we make. Get in touch today!

Contact us – Industrial Physics

FAQ

What does a leak test check for?

In the packaging world, a leak is a hole or a path through which the package contents may escape. Or through which environmental contaminants may enter. The process of quantifying a product leak is called leak testing.

How do you define a leak rate?

∆VLeakage (or Leak Rate) = ∆V (over) ∆t (where ‘V’ is the volume of the medium exiting or entering and ‘t’ is the time period you’re measuring the change in volume). To break the leak test formulae down in packaging terms. Take your sealed package; work out how much air or fluid escapes in a predetermined amount of time; then show it as measurements, such as cc/min, cc/sec, or ft3/hr.

What’s a pressure decay leak test?

With this type of leak test, the part being examined is pressurized. Meaning it’s filled with air until it reaches a set pressure. It’s then isolated from the supply pressure. Using a pressure sensor you then monitor the build-up within the part; as the air leaks out, the pressure drops. Next up you calculate the change in pressure over a certain period of time, which gives you: the leak rate.

What is mass flow testing?

Mass flow testing uses the intrinsic properties of air to directly measure the amount of it escaping a closed system. Through this type of leak test, the test part is pressurized, but you keep it connected to the supply pressure. On reaching an equilibrium – when the pressure in the part is stabilized – you’ll know that the gas flowing in from the supply is equal to the total leakage of gas flowing out.

What is occlusion leak testing?

An occlusion leak test will tell you if air or liquid is flowing as intended through the item. If it is – then the object’s passages are clear. If it’s not, then it’s likely you have a blockage – also known as an occlusion. An occlusion leak test works by trapping pressure inside your product and then measuring the release against an expected pressure loss. This pressure leak test begins straight after ‘the fill stage’ – as soon as you obtain the desired pressure. As the air or liquid leaves through the downstream port, it’s carefully measured. Then you compare the leak test results against your expected pressure decay for that item to determine whether it’s a pass or a fail.