Contributed by: Steve White - Test Engineering Manager
There are many considerations related to how a part is connected to a test station, and the test station to its supply of pressurized air, that can impact fill time. The shorter the fill time, the shorter the overall test. Shortening the test then allows you to reduce the number of test stations and staff required for leak testing to be an effective in-process test that keeps up with the pace of production on your line.
Fill time is determined by two things: the volume of space to fill within the part and how fast you can pump air into that empty space. Below are a few tactics to implement on your production line to reduce your leak test fill time.
Reduce fill time by making the part “smaller”
All the air volume in the leak tester and in the fixturing that is connecting it to the part, in addition to the part’s own internal volume, can contribute to a longer fill time.
To cut that fill time, we must make the part, in effect, smaller. To do this, you can engineer the fixturing to limit the internal volume that you need to fill for the test. You can achieve this by reducing the mechanical complexity of your test by shortening the distances between air supply, leak tester and part, and by simplifying the connections between the part and the tester. Larger diameters and shorter lengths of hose are ideal.
Consider the internal geometry of the part
If the part has numerous internal chambers that are separated by restrictions or small diameters, it’s often more efficient to connect to both sides of those chambers to fill them without having to force air through that internal restriction.
Look at the pneumatic connection to the part
When sizing connections between tester and the part, you want to make sure they can support the flow rates you need to fill the part quickly. Again, opt for larger diameter and shorter hoses.
Care must also be taken to select the right hose and connections to link the leak tester to the part without impacting the seal’s performance. It’s best to match the diameter of the fill port seal with the supply line from the leak tester. This maximizes the speed at which the part can be filled.
Manage test and supply pressure
How much air do you need to fill the part? Lower test pressures require less air and therefore mean you can fill the part faster. Higher test pressures lead to longer fill times. But changes to leak test specifications to achieve a lower test pressure must be carefully considered to ensure the repeatability and reliability of the test does not suffer as a result.
Take the fast fill approach
Another factor to consider is the supply pressure. The higher the supply pressure the greater the pressure drop across the regulators in the system. You can use this larger flow rate to your advantage to “fast fill” a part.
Pressurize the leak tester panel much higher than the test pressure you want in the part (even double) to overcome the pressure drop between the tester and the part. This allows you to fill the part quicker. You can then revert to maintain the desired leak test pressure in the case of a flow rate leak test.
Steve White addresses this subject as part of Sciemetric’s “Ask the Expert” video series. Click here to watch this video, "What factors influence the time it takes to fill a part before leak testing?", and more.