Helium Leak Testing for Vacuum Systems: How It Works and When You Need It

A vacuum system can lose performance for many reasons, but when air is entering through a failed seal, feedthrough, weld, valve, flange, or other opening, finding the exact leak location can be difficult.

A vacuum gauge can tell you that the chamber is not reaching the expected pressure. It cannot necessarily tell you where the problem is.

That is where helium leak testing becomes valuable.

Helium mass spectrometer leak detection provides a controlled method for identifying extremely small leak paths in vacuum chambers, pumping systems, valves, feedthroughs, fabricated assemblies, and other high-vacuum equipment.

YTI provides helium leak testing and vacuum leak detection for vacuum coating systems and components both on-site and through controlled testing at our facility.

What Is Helium Leak Testing?

Helium leak testing uses helium as a tracer gas.

During one common test method, the vacuum system or component is evacuated and connected to a helium mass spectrometer leak detector. Small amounts of helium are then introduced around suspected leak locations.

These may include:

• Chamber doors
• O-ring seals
• Vacuum flanges
• Welds
• Electrical feedthroughs
• High-voltage feedthroughs
• Viewports
• Valves
• Pump connections
• Vacuum tubing
• Flexible connections
• Instrumentation ports

If helium enters the evacuated system through a leak, the detector identifies the helium and provides a measurable response.

The technician can progressively isolate the source until the actual leak path is identified.

Why Is Helium Used for Vacuum Leak Detection?

Helium has several characteristics that make it useful for high-vacuum leak detection.

Helium atoms are small enough to travel through extremely small leak paths, while specialized mass spectrometer equipment can distinguish helium from the gases normally present in the surrounding environment.

This makes helium testing capable of detecting leaks that may be impossible to locate visually.

It also allows technicians to test specific areas instead of replacing seals, pumps, valves, or other components based only on suspicion.

What Equipment Can Be Helium Leak Tested?

Helium leak detection can be applied to individual vacuum components or an entire installed system.

YTI supports leak testing for equipment such as:

Vacuum Chambers

Chambers can develop leaks around doors, access covers, viewports, penetrations, flanges, instrumentation ports, welds, or modified areas.

Testing the chamber as an assembled system can help identify leaks that may not be visible during inspection.

Feedthroughs

Electrical, high-voltage, motion, fluid, and instrumentation feedthroughs can develop leaks through seals, ceramic interfaces, welded joints, or mounting connections.

Vacuum Valves

Valve body seals, shaft seals, actuator interfaces, and flange connections can all become possible leak paths.

Welded Vacuum Assemblies

New or repaired chambers, tubing, manifolds, adapters, and fabricated components should maintain vacuum integrity after welding or modification.

Helium testing can help verify that work before the equipment returns to production.

Diffusion Pump Systems

Diffusion pump installations contain multiple connections, forelines, valves, traps, heaters, seals, and chamber interfaces that can contribute to vacuum problems.

YTI also provides dedicated diffusion pump refurbishment and complete diffusion pump system support.

Vacuum Coating Systems

PVD, electron-beam evaporation, thermal evaporation, sputtering, and other vacuum coating systems contain many potential leak points.

In these systems, helium leak detection may be only one part of a broader diagnostic process.

Common Helium Leak Testing Methods

The correct method depends on the equipment and whether the component can be evacuated, pressurized, isolated, or tested in place.

Outside-In Testing

The component or system is placed under vacuum.

Helium is then carefully applied around suspected leak locations.

When helium enters through a leak, the mass spectrometer detects it.

This method is commonly useful for vacuum chambers and installed vacuum systems.

Inside-Out Testing

Helium is placed inside a test component or assembly.

The exterior is then checked to determine whether tracer gas is escaping through the vacuum boundary.

Sniffer Testing

A helium-sensitive probe can be moved around the outside of a pressurized component to identify escaping tracer gas.

Accumulation Testing

For certain applications, helium escaping from a component can be allowed to accumulate within a controlled enclosure before being sampled.

The best test method depends on the component, accessibility, required sensitivity, and operating conditions.

Signs Your Vacuum System May Need Leak Testing

Several symptoms can indicate that helium testing should be considered.

Your Pump-Down Time Has Increased

If a chamber historically reached operating pressure quickly but now takes significantly longer, a leak may be increasing the gas load.

There are other potential causes, however.

We cover those differences in more detail in our guide:

Why Your Vacuum System Won’t Reach Base Pressure: Leak or Something Else?

Your System Cannot Reach Its Normal Base Pressure

A system that stops pumping down at a higher-than-normal pressure may have a leak somewhere in the vacuum boundary.

Pressure Rises After Isolation

An unexpected pressure increase after isolating the chamber or a section of the system can indicate gas entering the volume.

Performance Changed After Maintenance

Any time flanges, seals, feedthroughs, pumps, valves, or chamber hardware are disturbed, there is an opportunity for a new leak to develop.

A Chamber Was Welded or Modified

Vacuum-boundary fabrication should be verified before relying on the system for production.

Equipment Was Relocated

Decommissioning and recommissioning a vacuum coating line requires disconnecting and reconnecting numerous vacuum interfaces.

Our related guide explains why leak verification should be part of the process:

Why Vacuum Systems Should Be Leak Tested After Repair, Welding or Relocation

Poor Vacuum Does Not Always Mean a Leak

This is one of the most important things to understand about vacuum troubleshooting.

A system that cannot reach pressure may have a leak.

But it could also have:

• Excessive outgassing
• Water vapor contamination
• Process contamination
• A virtual leak
• Weak mechanical pumping
• Diffusion pump problems
• Valve restrictions
• Cryogenic system problems
• Gauge errors
• Incorrect valve sequencing
• Process gas issues
• Control or instrumentation faults

Replacing seals throughout the system without confirming a leak can create unnecessary downtime without solving the problem.

That is why YTI approaches helium leak testing as part of complete vacuum-system diagnostics.

On-Site Versus In-House Leak Testing

Some equipment should be tested where it operates.

Large coating chambers, production systems, diffusion pump installations, and problems that appear only under the assembled configuration are often best evaluated on-site.

Other components can be removed and tested independently.

These may include:

• Feedthroughs
• Valves
• Pumps
• Fabricated assemblies
• Welded parts
• Vacuum fittings
• Modified hardware

The correct approach depends on the equipment and the symptoms being investigated.

What Happens After a Leak Is Found?

Finding the leak is only part of the repair.

The next step may involve:

• O-ring or seal replacement
• Flange repair
• Feedthrough replacement
• Valve repair
• Welding
• Brazing
• Vacuum fabrication
• Component refurbishment
• Pump service
• Chamber repair

YTI supports many of these services internally, which allows leak detection to transition directly into corrective work when appropriate.

After repair, the area can be tested again to verify vacuum integrity.

Helium Leak Testing From YTI

YTI has supported vacuum coating systems and high-vacuum equipment since 1984.

Our capabilities extend beyond operating a leak detector. YTI technicians work with the chambers, pumps, cryogenic equipment, electronics, valves, feedthroughs, instrumentation, and process hardware that make up complete vacuum systems.

That system-level experience is important when determining whether the problem is actually a leak and what should happen after the leak is found.

If your vacuum chamber is experiencing slow pump-down, poor base pressure, unexplained pressure rise, or performance problems following maintenance or relocation, visit our:

Helium Leak Testing & Vacuum Leak Detection Service

You can also contact YTI with the equipment manufacturer, model, normal base pressure, current pressure, recent maintenance history, and a description of what changed.