Problems like vacuum leaks, which might occur unexpectedly, can have disastrous effects on vacuum systems, operators, and the surrounding environment. It is essential to design a mitigation strategy before these occurrences so restore vacuum levels as soon as feasible.
What Exactly is a Vacuum Leak?
A vacuum leak is a minor opening in a system that allows gas to escape or enter without authorization. It ranges in severity depending on the size of the hole, the temperature, the kind of gas pushed through the system, and inside vs. outside pressure differentials.
A leak in a vacuum system reduces productivity and puts workers and goods in danger. A vacuum leak might have several unfavorable consequences.
- Substantial release of toxic substances into the environment
- Introduced contaminant.
- A broken system
Vacuum systems may operate safely and effectively without being vacuum-tight. They must maintain working pressure, gas balance, and ultimate pressure.
Vacuum Leakage Testing Techniques
The helium vacuum test, bubble test, pressure decay test, and pressure rise test are the four most common methods used to identify vacuum leaks.
- Tests with Bubbles
The tester submerges the object in the water and notes the location of the first bubble. A second approach involves pouring detergent around a leaky water or gas-filled object and labeling the area where bubbles occur.
- Pressure-Decay Tests
Pressure decay tests need the tester to evacuate a closed vacuum vessel to a certain pressure. The intake valve of the pump is closed and then reopened at regular intervals throughout the testing process.
The tester performs this procedure multiple times to assess how long it takes for the vacuum to recover to its original level. There is probably a leak present if the time keeps ticking along. Yet less time doesn't rule out the presence of a leak altogether.
- Pressure Increase Tests
The pressure decay test is like the pressure increase test. The tester compares the vacuum level to the time required to reach that level. A straightening of the curve indicates the presence of a leak.
- Helium Testing
The only way to find a leak smaller than 1x10-6 mbar *l/s is to test with helium. Helium's low mass, affordability, and inertness make it a tracer gas for testing.
How to Fix a Vacuum Leak
After detecting a vacuum leak and calculating its leakage rate, the testing process moves on to the repair phase. Fixing a system won't make it leak-proof, but it can get it back to where it needs to be in terms of vacuum performance to serve its intended function.
Seal failure and view glass/feedthrough problems account for most leaks.
- Vacuum Leak Repair Due to Seal Failure
Most vacuum system leaks originate at the seals that connect the system parts.
Most electrical feed-throughs, chamber doors, and pump line connections leak. All seals will eventually become brittle after being used for a few years.
Fixing this problem is easy; replace the faulty seal.
- Fixing a Vacuum Leak Between the Feedthrough and the View Glass
Glasses and feed-throughs are welded or cemented together. Leaks may form at the point where these materials join with others if the junction ages or develops cracks due to mechanical stress or temperature cycling.
View glass and feedthrough vacuum leaks are notoriously difficult to fix. In most cases, you'll have to swap out the parts. Nevertheless, low-degassing resins can sometimes patch view lenses and feed-throughs.
Welding the leak is the most effective method for sealing a vacuum vessel body or port. Welding a high-vacuum vessel is recommended to avoid releasing any of the vacuum's contained glasses.
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