You can’t see a leak. You can’t always hear it. But if you're working with a vacuum system, you can definitely feel it, usually in the form of performance issues, contamination, or headaches from trying to figure out why everything suddenly went sideways.
At Provac, we understand that leak rates and outgassing aren't just technical jargon - they're the quiet saboteurs of your high vacuum goals.
What Exactly Is a Leak (and Why It’s Not Always Obvious)
In the vacuum world, a leak isn’t a dramatic hiss or a puddle on the floor. It’s usually something sneakier. A leak is any unintended pathway that lets gas enter your vacuum system. That tiny crack in a flange? That slightly loose O-ring? Yep, those count.
Leaks matter because they can ruin your pressure levels, mess with process stability, and introduce contaminants that love to hang around way longer than invited.
Leaks fall into three main categories:
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Real leaks: A literal hole or gap in the system.
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Virtual leaks: Trapped volumes (like threaded holes) slowly releasing gas.
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Permeation leaks: Gases sneaking through materials over time.
Not all leaks are created equal—but they all interfere with how your vacuum performs.
Understanding Leak Rate and Its Impact on System Stability
A “leak rate” is the speed at which gas sneaks into the vacuum system. It’s usually measured in units like mbar∙L/s or Torr∙L/s. The lower the leak rate, the better the seal, which is why leak testing isn’t a maybe—it’s a must.
Here’s the thing: even a leak rate of 1x10⁻⁶ mbar∙L/s might be too much if you’re running a high vacuum application like semiconductor processing or electron microscopy. On the flip side, for a rough vacuum job like freeze drying, you might tolerate a bit more leeway.
The right leak rate depends on your process, but the wrong one? That’s trouble waiting to happen.
Why Outgassing Is Like the Ghost You Can’t Evacuate
Even if your vacuum chamber is perfectly sealed, you’re still not safe from system contamination. That’s where outgassing comes in.
Outgassing is when materials inside the vacuum system release gases (water vapor, hydrocarbons, solvents, and others) into the chamber. The catch? This can happen after you’ve pumped everything down and think you’re good to go.
Sources of outgassing include:
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Plastic parts (even cables and connectors)
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Adhesives and sealants
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Human fingerprints (yes, really)
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Internal welds or poorly cleaned components
It’s like your system is generating its own leak from the inside. And if you’re chasing ultra-clean environments, that’s a nightmare.
How the Outgassing Rate Affects Your Vacuum System
The outgassing rate is the measure of how much gas a material releases over time under vacuum. Even something as simple as a single drop of vacuum grease can outgas enough to delay your pump-down or disrupt your process.
For applications needing a pristine high vacuum, managing your outgassing rate is just as important as sealing external leaks. It’s why we emphasize cleaning components, baking out systems when necessary, and choosing low-outgassing materials in system builds.
In many high vacuum failures, outgassing, not a real leak, is the real culprit.
Helium Leak Detection: The Gold Standard for Sniffing Out Trouble
When it’s time to get serious about leaks, nothing beats a helium leak detector. Helium leak testing is precise, reliable, and ridiculously sensitive.
Why helium?
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It’s tiny so it fits through microscopic leaks.
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It’s inert so it doesn’t react or contaminate.
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It’s not naturally abundant in air so background levels stay low.
A helium leak test involves pressurizing the suspected component with helium and using a detector to sniff out escaping particles. Think of it as the vacuum world’s version of a bloodhound.
Helium leak detection is essential in industries like aerospace, medical, and electronics, especially anywhere reliability is life-or-death or cost-is-critical.
At Provac, we use helium leak testing not just to find leaks, but to validate repairs, certify equipment, and make sure your vacuum system performs as expected from day one.
Leak Tests That Actually Mean Something
Not all leak tests are created equal. A bubble test might work for checking your kid’s bike tire, but not your deposition chamber.
Here are the major types of vacuum leak testing that matter:
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Helium mass spectrometry: Ultra-sensitive and industry-standard
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Pressure rise tests: Good for spotting larger leaks but less specific
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Residual gas analysis (RGA): Helps track down outgassing components by identifying gas species present
We often recommend combining leak test methods for a full picture. Helium testing finds the actual breach; RGA helps you understand the system’s internal gas makeup.
Residual Gas Analysis: Understanding What’s Lurking Inside
Think of residual gas analysis like a forensic report of what’s floating around in your vacuum chamber. It tells you which gases are present, and often, where they’re coming from.
If you're seeing high water vapor peaks or mystery hydrocarbons, you might be looking at outgassing from polymers or contamination from unclean parts. If nitrogen levels are unexpectedly high, it could indicate a small air leak.
RGA is particularly useful after a leak test confirms the system is tight, but you’re still not hitting desired vacuum levels. It’s like your vacuum system is trying to tell you something—and RGA is how you listen.
Practical Steps to Control Leaks and Outgassing
You don’t have to be a vacuum whisperer to keep leaks and outgassing under control. Here’s what we recommend based on years of hands-on experience:
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Clean everything thoroughly before assembly. No shortcuts.
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Bake out the system if ultra-low pressures are needed.
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Use helium leak testing to validate every seal and flange.
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Choose materials with low outgassing properties (metal over plastic, PTFE over PVC).
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Replace old seals, especially Viton or rubber gaskets that have seen better days.
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Avoid over-tightening flanges, which can warp surfaces and cause future leaks.
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Watch for “virtual leaks” from tapped holes and blind volumes.
If you’re ever unsure where the issue lies, leak or outgas, we offer diagnostic services to pinpoint the exact problem and fix it without the guessing game.
