Leakage

Classification of tightness

Class	Maximum leak diameter	Leakage rate [mbar × l ⁄ s]	Leak time (for 1 cm3 bubble)
Technically tight	0.1 µm	1 × 10⁻¹¹	> 1 000 years
Gas-tight	0.8 µm	1 × 10⁻⁹	> 30 years
Virus-tight	3 µm	1 × 10⁻⁷	> 100 days
Bacteria-tight	10 µm	1 × 10⁻⁵	> 1 day
Water-tight	30 µm	1 × 10⁻³	> 15 min
Drip-tight	100 µm	1 × 10⁻¹	10 s
Running-water-tight	1 mm	1 × 10¹	0.1 s

Practical reminders for leak detection

• Use only small quantities of test gas (to avoid saturation of the detector).
• Start where you last modified the vacuum chamber.
• Work your way down top to bottom (because test gas is lighter than air).
• A long response time of the gas detector may be due to the spatial distance of the leak as well as propagation delay caused by small diameter tubing.
• However, if you have found a decent-sized leak, the response generally occurs immediately.