Leak Testing Objective – You Must Make a Choice!

Like almost everything, there is more than one way to tackle a challenge, reach a goal, or hit a target.Leak testing is no exception. Establishing your leak testing objective before beginning the process of leak tester selection is key. First, ask yourself: do I want to know IF it leaks or do I want to know WHERE it leaks?

Recently I’ve been asked on more than one occasion to help a medical device manufacturer to determine where their device is leaking and how badly it is leaking, i.e. the leak rate.

Both of those questions can be answered with great precision—but not at the same time and with the same processes.

Identifying the Leak Testing Objective for Your Application

Old-fashioned bubble testing where you submerge a device under water will identify the leak site immediately. Taking it a step up in sophistication you can use trace gas testing to get an APPROXIMATE idea of how much leakage there is at various sites in a device.

However, if the function of your device has very specific tolerances for overall leakage you will need to know with great accuracy the leak rate it produces. Test methods such as pressure decay and mass flow are example of techniques that make decisions on overall leak rates, these leak testing methods will tell you exactly how much your device leaks but they provide no information on where those leaks are occurring.

Sometimes there are assemblies that can be adjusted if they fail the leak test. These parts often have a lot of work built in already. By that I mean that the manufacturer has already applied labor and materials costs in their assembly and to discard them would be economically and environmentally disadvantageous.

An extreme example would be a car engine or transmission. A smaller example could be a gas burner for a grill.

A useful feature to be found on some of our leak testers is “Parts Grading”. Parts grading is available on– Vector, Optima^vT and Qualitek^mR. This feature allows the tester to grade test parts based on leak rate, or flow rate, (or any other quality capable of being measured by an electronic sensor provided that the tester can accept the input) and requires no additional test time and is designed to separate rejected parts from salvageable and or scrap. A typical use for this feature is as follows:

• Leak 0 – 10 sccm = Accept
• Leak >10 – 20 sccm = Salvageable
• Leak > 20 sccm = Reject,

It’s clear that this is a very useful feature and that the benefits it can bring may quickly justify the replacement of leak testers that do not have it.

An assembly with multiple parts may have many potential leak sites from porous materials, badly made joints, etc. and may need a combination of measurement and location test techniques. In this case production line testing is most expediently done by pressure decay or flow test measurement and only those parts that do not satisfy the overall test criteria are then tested by a location search technique.

For most people, especially those in high volume manufacturing or assembly situation, the choice comes down to speed of testing. Test everything as quickly as possible. If it leaks, then put it aside, try and identify the leak site, then scrap it, rework it or recycle it. Sometimes identifying the leak site is a time consuming and consequently overlooked step, but in many cases it is important – locating the site can identify process control issues or vendor quality problems.

A company like Uson that has leak testing equipment that can handle both scenarios will provide no-cost consultations on how to use one or another method for audit testing or testing of all production units and when.

Call or email me at joe.pustka@uson.com and let me help you make the right choice.