When to Use Differential Pressure Decay Leak Tests

By Charlie Bright, VP Sales (cbright@zaxisinc.com)


Various automated air leak tests are available to ensure quality on OEM production lines, but It can be a challenge to choose the best test for your operation. One of the most popular options is pressure decay leak testing, which introduces air into a part and measures the loss of pressure to find any present leaks.

Differential pressure decay leak tests are a specialized type of pressure decay air leak testing. Where a traditional pressure decay test measures pressure over time to identify leaks, differential pressure decay tests measure concurrent pressure changes between a reference volume and a test part volume using differential sensors.

How Does Differential Pressure Decay Leak Testing Work?

The exact steps for using a differential pressure decay tester on your production line will vary depending on your equipment. Generally, the test process will follow these steps:

1. Fill the test part and a reference volume with air until you reach the specified test pressure.
2. Shut both the test part and reference volume off from the air supply.
3. Allow the test pressure to stabilize, ensuring the isolation valves are closed.
4. Once pressure stabilizes, a differential pressure sensor, also called a transducer, will measure any changes between the test part and reference volume during a pre-set span of time.
5. When the test is completed, instrumentation will display the change in differential pressure.
6. Any remaining pressure is vented from the system.

If the loss of pressure stays within your predetermined values, then the part passes the test. If the part is outside those values, it has failed the test and requires further evaluation before moving to the next production stage.

When to Use Differential Pressure Decay Leak Tests

Differential pressure decay leak tests are helpful for large-volume parts that have low leak rates. As large volumes have large surface areas, they are more impacted by atmospheric changes. As differential pressure decay leak tests have test volumes of equal sizes on each side of the sensor, they can better account for fluctuations in pressure caused by temperature. The dual test volume will nullify external influences to produce reliable and precise results.

Examples of parts that benefit from differential pressure decay leak testing include:

• Components above 30 psig
• Large and/or non-expanding parts, such as engines and transmissions
• Parts with very small amounts of pressure loss, such as consumer electronics

In addition to these applications, differential pressure decay leak testing can be used to compare the leak rate of two parts or to improve test repeatability while decreasing cycle time.

Limitations of Differential Pressure Decay Leak Testing

Despite its highly accurate capabilities and sensitive operations, pressure decay leak testing is not the best solution for all production lines. The upfront cost is more expensive than a traditional pressure decay test because it requires extra pneumatic and sensing elements. It will also take more time to fill both parts simultaneously. For budget-conscious operations or lines with extreme time restrictions, differential pressure decay leak testing will not be suitable.

Modern pressure sensors and analog-to-digital converters (ADC) can now provide high-resolution results and work as a more cost-effective alternative to differential pressure decay leak tests, relegating differential tests to a smaller number of applications.

Zaxis is Your Full-Service Partner for Leak Testing Equipment & Knowledge

Zaxis is a leading USA manufacturer of innovative leak testing and dispensing solutions for automated manufacturing lines. If you are still determining if differential pressure decay tests are right for your operations or would like to learn more about other types of air leak tests, contact us today. A friendly member of our expert team will be in touch as soon as possible.