Sniffer Method Helium Leak Testing
The sniffer method is used when the test object cannot be evacuated — for example, large structures, installed systems, pressurised lines, or assemblies where creating an internal vacuum is impractical. The test object is pressurised with helium (or a helium-nitrogen mixture), and a probe (sniffer) is moved over the external surface to sample the ambient atmosphere. Any helium escaping through a leak is detected by the HELIOT mass spectrometer via the sniffer probe.
Sniffer Probes Compatible with HELIOT 900 Series
| Model | Type | Sampling flow | Hose length range |
|---|---|---|---|
| AS9 | Handy probe (pen type) | <0.03 slm (atmospheric) | 1–10 m (1 m increments) |
| BS9 | Flow rate probe | ~3 slm (atm.) | 1–10 m (1 m increments) |
| BT9 | Higher-flow probe | ~3 slm (atm.) | 1–10 m (1 m increments) |
The AS9 handy probe has a very small sampling area and is suited for precisely localising small leaks in accessible areas. The BS9 and BT9 have higher sampling flow and are suited for scanning larger surface areas more quickly. All sniffer probes connect via the sniffer port and hose; the hose length is specified at order and is not field-adjustable.
How the Sniffer Method Works
- Pressurise test object with helium or helium-nitrogen mixture. The test pressure must remain below the maximum safe working pressure of the component — typically 0.1–0.5 bar gauge helium overpressure is sufficient; higher pressure does not necessarily increase sensitivity and risks exceeding test object pressure limits.
- Allow equilibration time: helium takes time to diffuse out of small leaks and accumulate at the surface to detectable concentration. For tight leak thresholds, allow a few minutes before scanning.
- Scan the sniffer probe systematically over all suspect surface areas, welded joints, fittings, and seals. Move the probe slowly — sniffer response time depends on probe-to-surface distance and wind conditions in the environment.
- Identify and document leak locations where the HELIOT display shows elevated reading.
Limitations of the Sniffer Method
- Lower sensitivity than vacuum method: sniffer mode typical minimum detectable leak rate is in the 10⁻⁹ to 10⁻¹° Pa·m³/s range, versus 10⁻¹³ Pa·m³/s in vacuum ULTRA flow mode. This is 3–4 orders of magnitude less sensitive.
- Ambient helium accumulation: in confined spaces, helium released from leaks accumulates in the ambient air. This raises the background signal and can mask individual leaks. Ventilate the work area and allow background helium to clear between tests.
- Probe distance and scanning speed matter: the probe must be held close to the surface (within a few mm for AS9) and moved slowly enough for helium to be sampled. Scanning too fast or too far from the surface misses leaks.
- Not quantitative for total leak rate: the sniffer method localises leak positions but does not give a reliable total integral leak rate for a component.
Applications
- Installed piping systems and flanges (where evacuation is not possible)
- Large pressurised vessels and heat exchangers
- Valve bodies and fittings in operating systems (not under vacuum)
- Building HVAC systems (when part of the system is pressurised with tracer gas)
- Automotive fuel system assemblies at pressure
- Welded structures where one side is inaccessible for vacuum connection
- Field leak testing of installed equipment not connected to vacuum instruments
When to Use Sniffer vs Vacuum Method
| Factor | Vacuum method | Sniffer method |
|---|---|---|
| Sensitivity | Higher (<5×10⁻¹³ Pa·m³/s) | Lower (~10⁻⁹ Pa·m³/s) |
| Test object evacuable? | Required | Not required |
| Quantitative leak rate | Yes (integral total) | Limited |
| Localisation | Yes (spray in specific area) | Yes (probe position) |
| Large installed assemblies | Difficult | Practical |
| Helium required | Spray gas to outside | Tracer gas pressurised inside |
Service and Support
We supply sniffer probe units (AS9, BS9, BT9) and provide commissioning, calibration, and training for sniffer method testing applications. If you are evaluating whether the vacuum method or sniffer method is appropriate for your application, contact us with a description of your test object and acceptance criteria and we will advise.
Email: mail@ulvacheliot.com
Helium Leak Testing Guide | Vacuum Method | Calibration | HELIOT 900 Series