Quote:
Originally Posted by Philips210
I remember reading that helium is able to permeate through glass such as in valves and impair the vacuum. Is this a real possibility if the valve is exposed to helium?
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I recall that when I worked on sector-field mass spectrometers, a way of finding where there was a leak in the vacuum system was to squirt a little helium around the suspect places while the mass spectrometer was tuned to 4 mass units. If a peak at 4 mass units was seen, that was where the leak was. This was pretty sensitive, as most of the joints would leak a little, anyway.
Isn't it true to imagine that if helium can diffuse through the glass envelope of a valve, then it can also leak
out of the valve too? This will depend on the partial pressure of helium on either side of the glass, not the total pressure difference, surely?
Colin.