Fundamentals of leak detection Editor: Leybold GmbH Cat. No. 199 79_VA.02 Authors: Leybold GmbH Bonner Str. 498 · D-50968 Köln T +49 (0) 221-347-0 F +49 (0) 221-347-1250 [email protected] BICOM 13619.13810.19979_VA.02      0.2.12.16 mzs Printed in Germany on chlorine-free bleached paper     Technical alterations reserved Hans Rottländer Walter Umrath Gerhard Voss

Fundamentals of Leak Detection Leybold, a member of the globally active industrial Atlas Copco Group of companies has developed into the world market leader in the area of vacuum technology. In this leading position, we recognize that our customers around the world count on Leybold to deliver technical superiority and maximum value for all our products and services. This brochure is meant to provide an easy to read overview covering the entire range of vacuum technology and is independent of the current Leybold product portfolio. The presented product diagrams and data are provided to help promote...

Fundamentals of Leak Detection Leak rate, leak size, (gas) mass flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Helium standard leakrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Leak detection methods without leak detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Pressure rise test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Pressure drop test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12...

Fundamentals of Leak Detection Industrial leak test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Formulary for leak detection technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Pressure of a gas and pressure units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 9.1.1 Partial pressure - total pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 9.2 9.2.1 Equation of state for ideal gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

Fundamentals of Leak Detection Fundamentals of Leak Detection Introduction In addition to the actual vacuum systems and their individual components (vacuum vessel, lines, valves, measuring devices, etc .) there are numerous other systems and products in the fields industry and research with high requirements regarding tightness or so-called "hermetic sealing" . These include, in particular, assemblies for the automotive and refrigeration industry Generalized statements often made, such as “no detectable leaks” or “leak rate zero”, do not represent an adequate basis for acceptance testing Every...

Fundamentals of Leak Detection 2 Leak rate, leak size (gas) mass flow No vacuum device or system can ever be absolutely vacuum-tight and it does not actually need to be. The simple essential is that the leak rate must be low enough that the required operating pressure, gas balance and ultimate pressure in the vacuum container are not influenced. It follows that the requirements in regard to the gas-tightness of an apparatus are the more stringent the lower the required pressure level is. In order to be able to register leaks quantitatively, the concept of the "leak rate" with the symbol qL and...

Fundamentals of Leak Detection In order to achieve an overview of the correlation between the geometric size of the hole and the associated leak rate it is possible to operate on the basis of the following, rough estimate: A circular hole with a diameter D = 1 cm in the wall of a vacuum vessel is closed with a valve. Atmospheric pressure (p = 1013 mbar) prevails outside, a vacuum inside. When the valve is opened, the air flows at the speed of sound (vS = 330 m/s) through the opening cross section of A = p-(D2/4) - 0.79 cm2 into the vessel. The air quantity flowing into the vessel amounts to qL(air)...

Fundamentals of Leak Detection Estimates or measurements of the sizes of atoms, molecules, viruses, bacteria, etc. have often given rise to everyday terms such as “watertight” or “bacteria-tight” (see Table 1).

Fundamentals of Leak Detection 2.1 Helium standard leakrate Required for unequivocal definition of a leak are the pressures prevailing on either side of the (vessel) wall and the nature of the medium passing through that wall (viscosity, molar mass). For the case where the test is carried out with helium4 at a pressure difference of 1 bar from the atmosphere pressure (external) to the vacuum (p < 1 mbar, internal), which is frequently found in practice, the designation "helium standard leak rate" has been introduced in the standard DIN EN 1330-8. In order to indicate the rejection rate for a...

Fundamentals of Leak Detection 3 Terms and definitions When searching for leaks one will generally have to distinguish between two tasks: 1. locating leaks and 2. measuring the leak rate In addition, we distinguish, based on the direction of flow for the fluid, between the a. vacuum method (sometimes known as an "outside-in leak"), where the direction of flow is into the test object; the pressure inside the test object is less than ambient pressure and the b . positive pressure method (often referred to as the “inside-out leak”), where the flow takes place from inside the test object outward;...

Fundamentals of Leak Detection Fig. 4: Usage options for a vacuum leak detector based on the vacuum method (a, b) and based on the positive pressure method (c, d)

Fundamentals of Leak Detection 4 Leak detection methods without leak detector The most sensible differentiation between the test methods used is the differentiation as to whether or not special leak detection equipment is used. In the simplest case a leak can be determined qualitatively and, when using certain test techniques, quantitatively as well (this being the leak rate) without the assistance of a special leak detector. For example, the quantity of water dripping from a leaking water faucet over a certain period of time can be determined by collecting the water with a measuring vessel....