Vacuum Decay Leak Test Explained
By Lim Xu, Export Manager
A vacuum decay leak test places a package in a sealed chamber, draws a vacuum and watches for the chamber pressure to rise. Gas or vapor escaping through a leak causes that rise. ASTM F2338 describes it as a non-destructive method that needs no dye or tracer gas.
How does a vacuum decay leak test work?
The package sits in a test chamber that is evacuated and then isolated from the vacuum source. One or more pressure transducers then track the vacuum level and its change over time.
A rise in chamber pressure can come from a leak or from background noise. One is headspace gas drawn out of the package through a leak. The other is background noise, such as a flexible package expanding or residual gas released in the chamber and lines.
Liquid filled packages need one more step. Liquid can plug a leak, so the chamber is taken below the vaporization pressure of the liquid. Liquid in or near the leak then vaporizes and raises the chamber pressure.
Results are accept or reject. F2338 sets the limits by comparing baseline decay from control, non-leaking packages with leaking packages and with simulated leaks from a calibrated gas flow meter.
What affects vacuum decay sensitivity?
How small a leak the test can find generally depends on the package design, the transducer sensitivity, the design of the chamber and test system, and the test time and pressure.
- More sensitive pressure transducers can generally detect smaller leaks.
- Smaller void volumes in the chamber and test system tend to make pressure changes easier to detect.
- A longer test time can let smaller gas leaks show up.
- Lower background noise, for example from good masking or a chamber that limits package expansion, tends to improve sensitivity.
Chamber fit is usually a balance. Tooling that nests the package closely keeps the net chamber volume small, but it still needs to let gas flow around the package so leak sites are not blocked.
The package contents matter too. Test parameters have to suit whether the package holds liquid or solid, how much gas headspace it has, and whether it is flexible or rigid, porous or nonporous.
Questions about a model or a test? Email Amy Zhao, Export Manager, at [email protected].
Which packages suit a vacuum decay test?
The table below lists the four package groups covered by ASTM F2338 and one point to watch for each.
| Package group | Examples in F2338 | Point to watch |
|---|---|---|
| Rigid and semi-rigid non-lidded trays | Thermoformed PETE or PETG trays | Tray must nest closely without blocking gas flow |
| Trays or cups with porous lidding | Trays sealed with porous barrier lidding | Mask the porous lid; leaks in the lid itself are not detected |
| Rigid, nonporous packages | Screw cap bottles, vials with elastomeric closures, syringes | Hole defects of at least 5 µm were detected in the precision studies |
| Flexible, nonporous packages | Pouches and bags of polymer, foil or laminate film | They deflect under vacuum, so the chamber should limit expansion |
The detection limits in F2338 were found with the specific product and package systems used in its precision studies. A different package needs its own test parameters and its own sensitivity check.
How does vacuum decay compare with bubble emission?
USP <1207> sorts leak test technologies into deterministic and probabilistic groups. It places dye ingress and microbial challenge in the probabilistic group, because their outcomes carry some uncertainty. Vacuum decay works differently, since F2338 bases detection only on a measured pressure change in the chamber.
Bubble emission is a visual check for gross leaks. ASTM D3078 uses a transparent vacuum chamber and an immersion fluid to look for bubbles from flexible packages that contain headspace gas. The standard warns that small leaks may not be detected.
Our MFY-01 vacuum leak tester runs this ASTM D3078 bubble emission test. It is a different method from vacuum decay, because the operator watches for bubbles rather than measuring a pressure rise.
The MFY-01A fully automatic vacuum leak tester runs the same bubble emission method with automatic constant pressure compensation and a one-key full automatic cycle.
How is a vacuum decay test set up and checked?
Test settings are usually developed for each combination of package and test fixture, using control packages that are known not to leak. Sensitivity is then commonly checked against simulated leaks of known size or flow, so the test can tell non-leaking packages from leaking ones.
F2338 describes regular baseline and sensitivity checks during routine use. Check the current edition of the standard for how often to run them and what to report with each result.
Frequently asked questions
Can vacuum decay find leaks in the porous lid of a medical tray?
No. ASTM F2338 tests porous lidded trays for leaks in the tray and at the lid to tray seal junction. Leaks in the porous lidding material itself cannot be detected, and the lid is masked during the test.
Is vacuum decay only a production line test?
No. F2338 calls it a useful research tool for optimizing package sealing parameters and comparing packages and materials. It also suits production, either for 100% online testing or for statistical sampling.
Talk to our factory team
We sell direct from our factory, so you work directly with our factory team. Questions about a model or a test? Email Amy Zhao, Export Manager, at [email protected].