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Leak Detection for Vacuum Systems

Maintaining vacuum integrity requires more than just identifying leaks – it demands precise leak detection and localization. That is where helium spraying comes in.

As part of commissioning, maintenance, or repairs, it is essential to ensure quality and performance.

Helium spraying for accurate leak localization

In large vacuum systems, even small leaks can compromise performance, contaminate processes, or delay operations. A pressure rise or decay test often indicates that a leak exists – the next step is to detect the location quickly and reliably.

That is where helium spraying becomes essential. This detection method is highly effective across a wide pressure range and supports qualitative testing.

How helium spraying works

  • Initial check: Perform a pressure rise or decay test (also called leak-up test) to determine tightness. Bake out the system beforehand to minimize background outgassing.
  • Connect your vacuum system to a helium leak detector.
  • Spray helium externally on suspected leak zones like seals, welds, valves or flanges.
  • Detect leaks by observing detector signal spikes as helium enters the system.
Because it localizes rather than just confirms that leaks exist, helium spraying turns a 'leak detector' into a true leak finder.
Christian Burger, Market Manager at Pfeiffer Vacuum+Fab Solutions

Applications that rely on vacuum leak detection

Helium spraying is an essential leak testing method across a wide range of industrial applications – from semiconductor manufacturing to ultra-high vacuum (UHV) research environments.

Challenges in semiconductor manufacturing

  • Contamination from gas leaks or micro-leaks
  • Downtime in 24/7 production environments
  • Aging of o-rings due to thermal cycling

Challenges in systems building

  • Worker safety in gas-filled, confined spaces
  • Heat-related damage during treatment cycles
  • Difficulty locating leaks in complex connected systems

Challenges in UHV environments

  • Achieving and maintaining extremely low pressure levels
  • Detecting minute leaks in systems with many joints
  • Preventing contamination in ultra-clean environments

Semiconductor manufacturing

In semiconductor tools, maintaining vacuum integrity is critical – especially in connected systems used for deposition, lithography, or etching.

These vacuum processes run continuously under harsh thermal and mechanical conditions.

What helium spraying provides for the semiconductor industry:

  • Fast, real-time leak localization during ongoing operation
  • High sensitivity for detecting micro-leaks before damage occurs
  • Confidence in maintaining process stability and product quality

This approach is especially valuable in predictive maintenance programs for large vacuum systems operating in high-throughput environments.


Matching products

See how leak detection supports semiconductor uptime
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(e.g. vacuum furnaces or coaters)

Systems building

After assembly or maintenance, even small mistakes in component sealing can lead to major issues – particularly when dealing with reactive or hazardous gases like argon or chlorine.

Leaks often occur at junctions where valves, tools, or process-specific equipment are integrated into the system.

How helium leak detectors help in systems building:

  • Ensure safety and prevent gas exposure
  • Localize leaks quickly for faster repairs
  • Maintain product quality and prevent oxidation or defects
pvweb_224_leak_detection_of_systems_spraying_uhv_chamber_2

Ultra-high vacuum (UHV) environments

In ultra-high vacuum (UHV) systems operating at 10⁻⁷ hPa (mbar) and below, even the tiniest leak in flanges or welded components can disrupt experiments, delay results, or damage sensitive equipment.

Why helium spraying is crucial in UHV:

  • Enables precise leak detection in complex, tightly sealed systems
  • Supports the strict tightness requirements needed to achieve ultra-high vacuum (UHV) levels
  • Helps maintain clean conditions in sensitive setups like accelerators, electron microscopes, and coating chambers
uhv_chamber

Helium leak detectors from Pfeiffer

Find the right solution for your system.

Different environments demand different solutions – from compact service units to fully integrated, high-throughput lines. Leak detectors use helium mass spectrometry – but differ in size, mobility, throughput, and pump configuration:

  • Flexible system integration with the option to choose from various backing pumps (dry, oil-lubricated, or external) for different leak rates and chamber volumes (ASM 340)
  • Compact and portable designs ideal for mobile service, R&D, or tight spaces (ASM 310)
  • High-throughput models with maximum helium pumping speed for fast stabilization in cleanroom and 24/7 environments (ASM 390/392)
  • Dedicated tools and accessories help adapt your leak detector to changing conditions and workflows. From helium spray sets to transport carts – everything to optimize your testing setup

Compare matching products

Expert webinars: Insights to improve your leak detection for vacuum systems

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Outdated to Optimized – Upgrade Your Coater or Vacuum Furnace

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Leak Testing of Hermetically Sealed Objects – Revealing the Secrets

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Become a Leak Detective: Pro Tips for Vacuum System Leak Detection

Ready to master leak detection in vacuum systems? Learn more about the basic methods and how to apply them efficiently in your daily work!

Understanding leaks and basics

What causes leaks in vacuum systems?

Leaks can result from:

  • Damaged o-rings
  • Cracks or corrosion in flanges, valves, or welds
  • Improper installation or repair of components or vacuum equipment
  • Virtual leaks caused by trapped gases or porous materials

What is a virtual leak?

A virtual leak occurs when trapped gases (often water vapor) slowly release from cavities like screw threads or porous materials. Though not a real breach, this outgassing can mimic a leak.

They can be difficult to detect under partial pressure conditions and require highly sensitive methods for detecting leaks. High-accuracy helium leak detectors or extended monitoring are needed to identify them.

Can you use WD-40 in vacuum leak detection?

No. WD-40 leaves oily residues and contaminants in vacuum environments, especially below 1×10⁻³ hPa. Use isopropanol or other alcohol-based liquids instead – they evaporate cleanly and temporarily seal the leak, indicating its location.

Why is helium commonly used for detecting leaks?

Helium is the preferred tracer gas used across several methods of leak testing, especially in vacuum environments.

These are the reasons:

  • Inert and non-reactive
  • Extremely small in atomic size, ideal for micro-leaks
  • Rare in air (~5 ppm), allowing high sensitivity
  • Non-toxic and eco-friendly


However, improper handling can lead to background contamination and false positives.

Always:

  • Avoid spraying excess helium
  • Vent the spray hose before testing
  • Apply helium gently and precisely at suspected points

Preventing and managing leaks

How can I prevent leakages in my vacuum system?

  • Use materials suited to your pressure
  • Minimize joints, bends, and dead volumes in the design
  • Handle parts carefully during installation
  • Perform regular visual inspection of critical components in the vacuum system
  • Run bake-outs to remove trapped moisture and gases

What should I consider when selecting a leak detector and preparing the system for small leak testing?

  • Choose the method: Out of several methods you need to pick what fits best based on system pressure and target leakage rate.
  • Detector specs: Fast response time, high sensitivity.
  • Accuracy factors: Avoid virtual leaks, ensure good conductance.
  • Cleanliness: Pre-clean chambers and bake out if needed.
  • Safety: Faulty parts or procedures can compromise operator and product safety.
  • Document and manage collected information carefully for traceability.

Expert support: Not sure which setup is right for you?
Submit a request or visit our leak testing services for hands-on guidance.

How do I collect and document test results of my leak detector?

Modern helium leak detectors (e.g. ASM series) support:

  • Digital data logging
  • USB or Ethernet export
  • Built-in diagnostics and audit-friendly reporting

Helium leak detection methods and best practices

How accurate is the spraying method?

Among the available leak testing methods, helium spraying provides sufficient accuracy for detecting most relevant leaks. Helium spraying is for localization, not absolute rate measurement. It detects leaks down to approx. 10⁻⁷ to 10⁻⁹ mbar∙l/s – suitable for most vacuum applications.

Strengths:

  • Works during actual system operation
  • Ideal after pressure rise/leak-up tests
  • Quickly finds leaks impacting safety or performance

Spraying vs. sniffing: What is best for vacuum leak detection?

Helium spraying and sniffing are just two of several methods in vacuum leak testing. The choice depends on pressure conditions and whether the system is under vacuum or filled with air.

 
Helium spraying
Helium sniffing
Helium flow
Outside → inside
Inside → outside
Use case
Vacuum in the chamber
Pressurized chamber
Helium quantity
Small, controlled
Full pressurization

Most detectors support both modes. For vacuum leak detection, spraying remains the most efficient and cost-effective approach.

What affects response time in spray tests?

In large systems, helium may take time to travel through the leak path. Optimize by:

  • Using short, wide connections
  • Ensuring good conductance
  • Minimizing external pump flow resistance (partial flow setups may lower signal strength)

Leaks in connected components or under partial pressure may require longer stabilization.

Can I use alternatives for detecting leaks or air ingress?

Yes, especially when detecting leaks caused by ingress of air or other gases, alternative methods like Quadrupole Mass Spectrometers (QMS) provide additional accuracy.

QMS can detect gases like nitrogen, water vapor, or argon. Useful in diagnostics, pharma, and R&D environments, they analyze leaks via mass-to-charge ratio.

Practical use and setup of leak detectors

How do I adjust the helium spray gun correctly?

  • Set a gentle, controlled flow – just enough to create small bubbles in water
  • Purge any accumulated helium in the hose away from the test object before starting
  • Target only likely leak points (flanges, o-rings, welds)
  • Avoid large gas releases that might trigger false readings

Choosing the right helium leak detector for spraying

Your choice should reflect your setup requirements – including mobility, response time, pumping speed, and integration flexibility:

  • ASM 340:A versatile platform designed for system qualification and mid-sized setups. Offers high helium pumping speed and can be equipped with a variety of backing pumps – dry, oil-lubricated, or external – to match different chamber sizes and leak rate requirements.
  • ASM 310:A compact, lightweight solution optimized for service, R&D, and tight spaces. Features multiposition operation, easy handling, and a removable touchscreen interface. Best suited for mobile or flexible setups where portability and quick deployment are key.
  • ASM 390 / 392: Designed for cleanroom use and 24/7 high-throughput operations, these models deliver the highest helium pumping speeds in the portfolio. Ideal for time-sensitive processes requiring rapid stabilization, such as semiconductor production or automated QA stations.

All models support both helium spraying and sniffing modes and can be adapted to different environments. Contact us to configure the most suitable leak detection solution for your vacuum system.

What accessories help optimize helium leak testing?

The right tools can make helium leak detection more precise and efficient.

Key accessories include:

  • HeliSpray: A refillable spray unit for accurate helium application on seals, valves, and welds.
  • Low-flow spray guns: Ensure controlled helium release, reducing false signals and improving detection accuracy.
  • Transport carts and boxes: Protect and mobilize your leak detectors and sensitive components.
  • Modular trolleys: Ideal for flexible test setups in laboratories or production environments.

These accessories help improve test results, support safe handling, and make your leak testing setup more adaptable.