{"id":94,"date":"2026-11-01T09:00:00","date_gmt":"2026-11-01T01:00:00","guid":{"rendered":"https:\/\/panovacuum.cn\/blog\/helium-leak-test-vs-pressure-rise-en\/"},"modified":"2026-11-05T16:29:33","modified_gmt":"2026-11-05T08:29:33","slug":"helium-leak-test-vs-pressure-rise-en","status":"publish","type":"post","link":"https:\/\/panovacuum.cn\/blog\/helium-leak-test-vs-pressure-rise-en\/","title":{"rendered":"Helium leak testing and pressure-rise testing differ by five orders of magnitude"},"content":{"rendered":"

A common question is whether pressure-rise testing is acceptable. It answers whether a chamber leaks; helium mass spectrometry answers how much and where. The gap is five orders of magnitude \u2014 a limit of the method, not of the instrument price.<\/p>\n

1. Leak rate turns tightness into a number<\/h2>\n

Q = \u0394p\u00b7V\/\u0394t. A 1 m\u00b3 vessel changing 1 Pa in 1 s carries 1 Pa\u00b7m\u00b3\/s. For scale: a 4 L bicycle inner tube losing 1 bar over 30 days is 1.5\u00d710\u207b\u2074 Pa\u00b7m\u00b3\/s; a refrigerator leaking 10 g of R134a over ten years is 7.1\u00d710\u207b\u2077. The refrigerator is two orders tighter than the tube and still far from a semiconductor chamber.<\/p>\n

2. Pressure rise measures more than leakage<\/h2>\n

With the valve closed, the rising pressure contains real leakage plus wall outgassing. Water outgassing decays as 1\/t, approximately 3\u00d710\u207b\u2079\/t (hours) in mbar\u00b7L\/(s\u00b7cm\u00b2). A freshly cleaned chamber can outgas several orders above its true leak for hours, so the reading is outgassing, not leakage, unless the background is measured and subtracted first.<\/p>\n

\"Final
Final leak test: helium spray performed unloaded, with readings and instrument model written into the record.<\/figcaption><\/figure>\n

3. Units differ by a factor of ten<\/h2>\n

1 mbar\u00b7L\/s = 0.1 Pa\u00b7m\u00b3\/s. Reading 1.5\u00d710\u207b\u2074 Pa\u00b7m\u00b3\/s as 1.5\u00d710\u207b\u2074 mbar\u00b7L\/s relaxes the requirement tenfold. Units in a contract matter more than the instrument model.<\/p>\n

4. Temperature is not in the formula<\/h2>\n

Q = \u0394p\u00b7V\/\u0394t has three quantities and no temperature term; the source material neither discusses temperature effects on pressure rise nor provides a correction (not covered). Any claim of temperature compensation should come with the formula.<\/p>\n

5. Why helium testing reaches 10\u207b\u00b9\u00b3<\/h2>\n

The mass spectrometer must operate below 10\u207b\u2074 hPa, maintained by the instrument’s own pumps. The turbopump compresses air far more than light gases, so air is held back while helium passes \u2014 it acts as a selective filter rather than a pump. Counterflow covers 1 to 10\u207b\u2079 Pa\u00b7m\u00b3\/s and dominates production use; main flow is more sensitive but needs 10\u207b\u00b2 hPa on both specimen and instrument. A quartz-window variant uses a 7 \u00b5m SiO\u2082 membrane with a 5\u00d710\u207b\u2079 detection limit.<\/p>\n

6. What each method can reach<\/h2>\n

Spray helium outside an evacuated specimen: < 5\u00d710\u207b\u00b9\u00b3 Pa\u00b7m\u00b3\/s at a 1000 hPa differential. Sniffing a pressurised specimen: < 1\u00d710\u207b\u2078, specimen must withstand overpressure. Accumulation: mainly above 1\u00d710\u207b\u2075, and slow. For a 10\u207b\u2079 verdict only vacuum-mode mass spectrometry qualifies; sniffing is floored by the 5 ppm helium naturally present in air.<\/p>\n

7. Large chambers test slowly<\/h2>\n

In molecular flow (< 10\u207b\u00b3 hPa) speed is set by specimen volume and effective helium pumping speed; above 1 hPa, laminar flow puts the backing pump in charge and everything slows. Longer waits on large chambers are geometry, not operator error \u2014 plan the response time into the schedule.<\/p>\n

8. Three sources of misreading<\/h2>\n

5 ppm atmospheric helium; helium dissolved in oil-sealed backing-pump oil diffusing back into the high-vacuum side (open the gas ballast after a large leak); and no purge after a strong signal.<\/p>\n

9. How we do it<\/h2>\n

Helium mass spectrometry against the criterion agreed on the project drawing. The capability we publish is the 1\u00d710\u207b\u2079 Pa\u00b7m\u00b3\/s range, with every unit tested rather than sampled. The method references GB\/T 36176-2018 and GB\/T 32218-2015, and the report is dispatched with the chamber. Pressure-rise testing is not used as an acceptance criterion here for one reason: it cannot separate leakage from outgassing, nor account for temperature error. For process judgement and rough localisation it remains entirely adequate; the sheet that gets signed calls for helium.<\/p>\n

Leak testing is a verdict, not a step. A verdict that cannot be stated precisely makes the report meaningless. The same verdict applies to your project once a drawing is submitted.<\/p>\n

Frequently asked questions<\/h2>\n

Can pressure-rise testing replace helium leak testing?<\/h3>\n

For process judgement, yes; as an acceptance criterion, no. The pressure-rise method cannot separate leakage from outgassing and carries no temperature correction. The document you sign has to rest on helium testing.<\/p>\n

What magnitude can helium leak testing reach?<\/h3>\n

External helium spray in vacuum mode reaches the 5\u00d710\u207b\u00b9\u00b3 Pa\u00b7m\u00b3\/s range. Our factory acceptance testing follows the criterion on the project drawing; the capability we disclose externally is the 1\u00d710\u207b\u2079 Pa\u00b7m\u00b3\/s range.<\/p>\n

Why does a large chamber take so long to test?<\/h3>\n

In the molecular-flow regime (below 10\u207b\u00b3 hPa) the response time is governed by chamber volume and effective helium pumping speed (V\/S). Above roughly 1 hPa, in the viscous regime, it is governed by the backing pump \u2014 the larger the chamber, the slower the response.<\/p>\n","protected":false},"excerpt":{"rendered":"

A common question is whether pressure-rise testing is acceptable. It answers whether a chamber leaks; helium mass spectrometry answers how much and where. The gap is five orders of magnitude \u2014 a limit of the method, not of the instrument price.<\/p>\n","protected":false},"author":1,"featured_media":115,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,4],"tags":[],"class_list":["post-94","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-en","category-leak-testing"],"_links":{"self":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts\/94","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/comments?post=94"}],"version-history":[{"count":3,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts\/94\/revisions"}],"predecessor-version":[{"id":149,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts\/94\/revisions\/149"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/media\/115"}],"wp:attachment":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/media?parent=94"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/categories?post=94"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/tags?post=94"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}