Bubble Leak Testing using an acrylic vacuum chamber

Bubble Leak Testing or Bubble Emission Testing is a procedure where leaks are visually detected and located through the emission of bubbles while the test specimen is submerged in water. In this article, we will talk about using an acrylic vacuum box as a leak detection device. We are also going to talk about the advantage, disadvantage, and the bubble leak emission test procedures.

What is a Bubble Leak Test

Bubble Leak Testing using an acrylic vacuum chamber
Bubble Leak Testing using an acrylic vacuum chamber

Also known as a bubble emission test, submersion leak test, underwater immersion leak test, or “dunking test” is a testing method of detecting and locating leaks in the specimen through the emission of bubbles. There are two ways to perform a bubble emission leak test: Pressurized and Non-Pressurized. The pressurized method is when the test specimen is pressurized above the ambient pressure, depending on the altitude of the test, the gauge pressure can be as high as the test allows. The specimen may be pressurized through sealing or through the feed through tubes connected to the test specimen while the bubble leak test is performed. The advantage of pressurizing the part is a better leak detection due to the additional pressure which is induced onto the test sample. The disadvantage is that this test is of higher complexity than the non pressurized method. However, the pressurized leak testing method may be the way to go due to test requirements. The Non-Pressurized test method on the other hand, does not require any additional pressurizing of the test sample and therefore can be advantageous due to the test simplicity that it offers over the pressurized method.

The bubble leak test works as a result of the pressure difference between the test part and the chamber. When a leak is present, the gas inside the part will flow from a higher pressure toward a lower pressure. Therefore, the submerged part will emit gas bubbles, which will be detectable visually. The larger the leak, the larger and more frequent the gas bubbles will escape from the specimen. The accuracy of the bubble leak test is in the neighborhood of 10-3 atm-cc/sec. A hole size as small as 0.001 inch or 0.025 mm in diameter can be detected with the immersion leak test. Holes of this size cannot be detected with the naked eye, they would have to be at least 25 times larger to be seen. This leak detection accuracy is as good or better than pressure decay leak test, air decay leak test, dye penetration test, or flow rate leak test but not better than the high vacuum helium leak test, gas sniffing methods, or the tracer gas leak test.

Bubble Emission Leak Testing Equipment

ASTM D3078 Standard Test Method for Determination of Leaks in Flexible Packaging by Bubble Emission
ASTM D3078 Standard Test Method for Determination of Leaks in Flexible Packaging by Bubble Emission

The most ideal bubble leak testing equipment is an acrylic vacuum chamber due to the fact that acrylic is transparent which enables a full view of the interior during testing. It is also the most cost effective and the best bang for the buck when it comes to accuracy of detection.

This acrylic chamber has to be coupled with a vacuum pump which is either a rotary vane pump or a venture pump. The Rotary Vane pump is powered by electricity, will pull a higher vacuum (30 in Hg), and does not require a pressurized supply air to run. A Venturi Pump on the other hand, does not require electricity, will pull a good vacuum (28 in Hg), and will require a pressurized air line. Whether you decide to go with a rotary vane pump or a Venturi pump will depend on your utilities and test requirements – there is no right answer here, both are very viable options.

To recap, the advantages of bubble emission leak testing are:

1. Cost Effective:
When it comes to product seal or closing integrity, there are no better methods for your wallet than the water immersion leak test. In fact, the next best method is an order or two of magnitudes more expensive.

2. Simple and Easy:
Placing your test specimen into a water bath, pulling a vacuum, and looking for bubbles is a pretty simple way of detecting and locating leaks. This is advantageous because production line operators without much training can perform this test.

3. Practical:
All that is needed is an acrylic box and a vacuum pump to perform this test. The accuracy of the test is pretty good for most commercial and medical packages.

4. Detection:
Leaks can be detected and located.



The Disadvantages of bubble emission leak test are:

1. Destructive Test:
Even though the inside of the package is not damaged or destroyed by water, bubble immersion leak test is considered a destructive test.

2. Subjective:
The bubble emission requires the involvement of a testing person. This induces subjectivity into the testing method. The testing operator must be engaged and involved in the test otherwise the false positives may ensure.

3. Preparation and Handling:
The test specimen must be cleaned and prepared for the leak test. Also, some may not like the inconvenience of dealing with wet parts.

4. Specimen Dependent:
Products which are sensitive to water, such as electronic equipment, may not be suitable for this testing method. Leaks cannot be quantified, there is no way to know how large or small the leak is, only where it is.

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