The Pioneer of Modern Leak Testing

No More Monday Blues For Leak Testers

Anyone reading this who is involved in the leak testing of flexible packages will be familiar with the methylene blue dye leak test. For years it has been the go to test for detecting leaks in flexible packaging – foil or laminate pouches, bags, blister packs, lidded trays, flow wrap

The Pursuit of Excellence.

“We are what we repeatedly do. Excellence, therefore, is not an act but a habit.”

— Aristotle

I came across this quotation recently and it quickly struck me how it relates to quality assurance. And so, with it being the beginning of a new year, this post is rather more

Leaks in Perspective.

In this post I thought we might try to put hole sizes,leaks, and leak rates in perspective. Much continues to be written about determining realistic leak specifications and the chestnut of the “no leakage permitted” type of specification is still commonly encountered.

Looking through some old training material I thought

How to Convert Bubbles to Flow Units

Probably the simplest type of leak test is still the dunk test wherein a part is connected to an air supply and held underwater while the operator looks for bubbles. Of course the disadvantages of this method are well known and technology has introduced non-destructive and more objective tests. As

Leak Testing Medical Devices Is Not For The Faint of Heart.

I think I have said this before; medical devices can present some of the greatest challenges in leak testing. That’s kind of ironic in a way, since they are often among the smallest things we are asked to test. The sheer variety is mind boggling. You can easily be forgiven for wondering where they all go with a visit to just one manufacturer.

Because they perform vital often life saving functions, it’s no surprise that testing them correctly is vital. If even one bad part reaches a patient the consequences can be catastrophic. This leads us to the first challenge:-

One hundred percent inspection

In some industries although the quality engineer seeks perfection there can exist a compromise between inspection and throughput by using statistical sampling methods. In the medical device industry perfection and production objectives must be met without compromise. Therefore fast, one hundred percent inspection is expected and it demands multi channel leak testers as well as accurate and reliable fixturing.

Everybody knows that medical device manufacturing is a highly regulated industry. It’s for the safety and peace of mind of patients, not just in the USA, but around the world. No one would argue that’s not a good thing. However, it brings with it ever increasing requirements for capturing and storing data. Some devices are serial numbered, chipped, or bar-coded and that brings us to the next challenge:

What Could Possibly Go Wrong?

Although much of modern leak testing was born out of rocket science, it’s not rocket science as they say. We’ve come a long way since automated leak testing started to become established, Nevertheless, it still sounds so easy – just fill something with air or gas and monitor the pressure

Viscosity – Keeping Leaks Real

Fluid handling is a subject worth having its own specialized category of engineers, so it would be foolish to try and discuss it in detail in a short affair like this blog. However, we can’t simply ignore its importance as it relates to leak detection.

As leak detection specialists we are concerned with dynamic viscosity, the resistance to flow when an external force is applied.

In very simple terms viscosity is a measure of attachment to the neighbouring molecules. The net result is that a more viscous liquid or gas will pass through a hole more slowly than a less viscous one.

Units of Measure

To complicate things, there are different units of measurement for different fields of study. For leak testing geeks our unit of measure is the PASCAL seconds (Pa.s) which may also be expressed as the Newton second per square metre (N s/m2) or as the kilogram per metre second (kg/(ms)). You’ll also come across the poise (P) and centipoise (cP)

1 cP = 10-2 P = 10-3 Pa s

The viscosity of a liquid or gas is determined by the strength of attraction between molecules. The following equation may be used to calculate the ratio between a liquid and gas:

Note: This assumes laminar flow characteristics, which should be verified in practice.

More on Reject Limits

In last week’s blog we discussed the plight of a fuel rail manufacturer trying to work with a very small reject limit. I received several questions about the wisdom of setting up such a test in the first place and so this week I am going to elaborate on leak rate specification.Here are some things to consider when creating a leak test specification.

Is it fit for purpose?

Over the history of modern leak testing, collectively the industry has solved probably tens of thousands of leak testing applications, even more, and a sort of unofficial playbook has emerged for pressure decay leak testing and other methods. Your supplier’s application engineering group is aware of these specifications in one form or another. Here are some examples:

Clearly there is a benefit in selecting a specification that reflects the actual usage conditions. This is where it’s possible that things can become a little difficult. Of course I am referring to the catch all demand that “it must not leak!”. For the record, once again, everything leaks, it’s just a matter of degree. If we corner ourselves by insisting on the tightest specification possible we are inviting trouble and unnecessary expense.

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