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Chapter 8

Summary Leak detection

In recent decades, the importance and extent of control of the leak tightness of devices, systems, components, storage tanks, etc. has greatly increased, not only in the vacuum industry and in industries where vacuum traditionally plays an important role, but also and especially in industrial processes not directly related to vacuum activities. The ever growing number of economically or environmentally demanded applications of tightness control in industry and science has made leak detection a more or less independent discipline. With respect to the Dutch version of this book from 2000, the chapter is totally revised and contains significant innovations. Thus, in leak proving/finding with helium as a tracer gas the main flow principle has come off worst with respect to the counterflow principle. This is mainly because of the more robust system, less chance of contamination of the mass spectrometer and the user-friendliness. Leak detectors according to the main flow principle are still extensively used in the laboratory environment, but are no longer commercially available. Furthermore, the palette of inside-out sniffing systems has greatly expanded. In addition to the long-standing helium and halogen sniffers, the hydrogen leak detector, quartz window sensor and several multigas sniffing systems, such as the infrared leak detector, are now on the market. Finally, two newly developed inside-out detection methods are added, the so-called ‘atmosphere method’ and ‘bombing’. All detection methods are evaluated for their sensitivity, response time, ease of use and overall employability.

Some figures in Leak detection

Leak detection - Control of cast aluminium car rims on gas-filled cavities by leak test — Industrial helium leak test plant for control of cast aluminium car rims on gas-filled cavities

Leak detection - 180° magnetic deflection spectrometer; insert in a helium leak tester — Simple 180° magnetic deflection spectrometer tuned to helium. For clearness sake the magnet is omitted. The magnetic field is perpendicular to the plane of motion of the helium ions

Leak detection - Helium leak detector in counterflow circuit — Schematic diagram of a helium leak detector according to the counterflow principle

Leak detection - Helium leak detector connection options — Connection options of a helium leak detector to a high vacuum system

Leak detection - Sketch of a quartz window sensor leak detector — Cross-sectional sketch of a quartz window sensor with the thin quartz window on the left side. For clearness sake the magnet is omitted. The sketch is made at the stage that the Penning gauge still needs to be pumped to UHV through the glass tube (top right) and subsequently sealed at the constriction. 1 – constriction, 2 – quartz window, 3 – anode, 4 – cathodes

Leak detection - Infrared leak detector — Schematic layout of an infrared leak detector

Contents Leak detection

8.1      Introduction 520
8.2      Conceptual considerations; leak rate 521
8.3      Leak detection methods 523
8.3.1   Pressurizing (inside-out) methods 524
8.3.2   Reduced pressure (outside-in) methods 526
8.3.3   Atmosphere method versus bombing 529
8.4      The use of helium as a tracer gas 532
8.5      Reviewing the symptoms; troubleshooting 535
8.6      Leak testing and leak finding 537
8.7      Helium leak detectors 538
8.7.1   The mass spectrometer 538
8.7.2   The pumping system 540
8.7.3   Response time 543
8.7.4   Sensitivity 546
8.7.5   Reference leak 548
8.8      Leak detection by vacuum gauge or RGA 549
8.9      Inside-out sniffing systems 552
8.9.1   Helium sniffer 552
8.9.2   Hydrogen leak detector 553
8.9.3   Quartz window sensor 555
8.9.4   Halogen leak detector 556
8.9.5   Multigas sniffing systems 558
8.10    Leak detection of (ultra-)high vacuum systems 559
exercises

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