FROM THE ENGLISH BOOK
Select a technique from the product requirement, pressure direction and demonstrated measurement capability. A detector specification alone does not establish what the complete test can detect.
Start with the product and the decision
Specify the unacceptable leakage, tracer gas, pressures on both sides of the wall, temperature, preparation and acceptance rule. Check shell strength and buckling resistance before evacuation or pressurisation. Conditions from a particular industry or standard apply only within their established scope.
Vacuum and tracer-gas configurations
- Vacuum chamber: tracer gas inside a dry product, vacuum outside. Check the product and chamber strength, leakage limit and external reference flow.
- External pressure chamber: vacuum inside the product and gas outside. Check buckling resistance, gas composition and complete coverage.
- Helium spray: vacuum inside with local tracer application outside. Establish response time and localisation behaviour; quantitative measurement requires known gas composition and response.
- Helium sniffer: gas inside with sampling outside. Verify dynamic detection capability, probe distance, scanning speed and gas capture.
- Local vacuum chamber: a chamber over an area with tracer gas on the opposite side. Verify seals, overlap and response.
Other techniques require their own controls
For bubble testing, verify liquid compatibility, observation conditions, access and detection capability. Atmospheric accumulation depends on free volume, time, mixing, gas composition and losses. Pressure-change testing requires stabilisation and control of temperature, volume, fixture background and gauge accuracy.
Helium bombing of sealed enclosures depends on exposure and measurement durations, internal volume, the flow model and gross-leak behaviour. Thermal vacuum testing requires agreed temperature conditions, background and detection checks at each test condition.
Record the conditions that make the result meaningful
Document preparation, pressures, gas composition, check-leak verification, timing and evaluation criteria. Report a result within the demonstrated capability and configuration; an absent response does not prove zero transfer of matter.
Adapted from English book preview · pages 18–19; original pages 124–125. This online article is an edited summary of selected material.