International Union for Vacuum Science, Technique and Applications VISUAL AIDS PROGRAM of the International Union for Vacuum Science, Technique and Applications Module 6 LEAK DETECTION © 2004. IUVSTA 1.00

Section 1 Introduction to leak detection © 2004. IUVSTA 1.01

Leak detection has many applications ICs LCD Displays Medicine Industry Automotive Aviation Semiconductor technology © 2004. IUVSTA 1.02

Small defect sizes cause leakages Typical leakage 10-2 mbar l/s Typical leakage 10-7 mbar l/s A micron- sized hole Cross-section of a human hair © 2004. IUVSTA 1.03

Typical leak rate ranges for detectors Pressure drop Pressure rise Ultrasonic - Bubbletest He – sniffing leak detection He – vacuum leak detection Bubbletest 10-12 10-11 10-10 10-9 10-7 10-8 10-6 10-5 10-4 10-3 10-2 10-1 100 101 H2 - sniffing leak detection SF6 – vacuum leak detection SF6 – sniffing leak detection Notes 1/ This slide was taken from the 1st Edition slide 06-038 augmented by some special modern methods. © 2004. IUVSTA 1.04

Acceptable leakage rates for bike tyres? Want a maximum pressure drop of 1000 mbar over 175 days before repumping tyre! Volume = about 1.5 Litre 175 days = 1.5 x 107 seconds What then is the maximum acceptable Leak rate? © 2004. IUVSTA 1.05

Example: a tyre leak rate in mbar l/s Formula: Unit: = mbar l s-1 qL=[V * (p2 - p1)] / t [qL] = mbar l s-1 – Leak rate [V] = l - Volume Test part [p1] = mbar – pressure at the start of the (measurement) period [p2] = mbar - pressure at the end of the elapsed (measurement) period t - s © 2004. IUVSTA 1.06

Leak rate conversion tables UNIT mbar l/s Pa l/s Torr l/s lusec cm3/s cm3 /hour kg/hour Air g/year R12 1 100 0.75 751 3560 4.3E-3 1.55E5 0.01 7.5E-3 7.51 0.99E-2 35.6 4.3E-5 1.55E3 1.33 133 1000 1.32 4738 5.7E-3 2.1E5 1.33E-3 0.133 1E-3 1.32E-3 4.74 5.7E-6 2.1E2 1.01 101 0.76 759 3600 cm3 /hour 2.81E-4 2.81E-2 2.11E-4 2.11E-1 2.7E-4 1.21E-6 4.30E1 230 23000 175 1.75E5 8.29E5 - 6.4E-6 6.4E-4 4.90E-6 4.80-3 2.3E-2 Notes 1/ This table derives directly from the 1st Edition of the IUVSTA Visual Aids Module 6, slide 06-039, with additional comments on the CFC replacement of R12 by the present author. 2/ The conversion table assumes units of Pressure x Volume / Time are at normal temperature (Tn), while the units of Volume / Time are at both Tn and normal pressure Pn=1013mbar. The table shows that 1mbar.l/s (Tn) = 0.99 cm3/s. (Tn.Pn). In actual practice one generally uses 1mbar.l/s = 1 cm3/s (Tn.Pn) = 1 std.cc/s. 3/ The temperature of the Air in the conversion table is 20°C 4/ R12 is Freon 12, chemical formula CCl3F. This material is banned under the Montreal Protocols on CFC elimination. Other refrigerants, blowing agents and propellants are now used in their stead, for which the g/year value will be different by the scaling factor provided by the inverse ratio of their molecular weights to R12 (Mol weight= 135.5). Thus R134a, which is an HFA molecule containing no chlorine atoms, having Mol weight= 102, has higher g/year for the given Pressure x Volume / Time unit by the scaling factor = 135.5/102 © 2004. IUVSTA 1.07

Typical limits for vacuum components Absolute Pressure range in Vacuum leak tightness units = mbarl/s Components used in systems Rough vacuum 1000 to 1 mbar < 10-5 Backing valves roughing valves Medium vacuum 1 to 10-3 mbar < 10-7 Vapour boosters foreline traps High vacuum 10-3 to 10-7 mbar < 10-9 Secondary pump bodies & valves Ultra-high vacuum < 10-7 mbar < 10-10 Bakeable valves; UHV component Notes 1/ This slide was taken from Mass Spectrometer leak detectors published by Edwards High Vacuum International. The material was gleaned from production tests and is merely indicative of the scale of leak tightness tested. © 2004. IUVSTA 1.08