The helium tric is good because

1: The molecule is very small. i mean you look for very very small leaks in high pressure / lo vaccum systems that way.

2: It is easy to detect in mass spectometers, a likely target to try to find leaks in


I suggested earlier to use CO2 or Oxygen, but same principle/cheaper detector.

Th Helium detector usually works on the principle of the cooling effect of 1 micron wires in a bridge configuration.
-----Ursprungligt meddelande-----
FrŒn: Snail Instruments <snail@IOL.CZ>
Till: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Datum: den 30 juni 1999 18:19
€mne: Re: Leak Detection...


>>  I seem to recall that one approach to tiny air leaks is to consider
>>that the wavelengths of sound emitted are likely to be comparable to the
>>size of the defects.  This suggests that you might look for *ultrasonic*
>>frequencies for starters.
>
>I am affraid that the (ultra)sound volume will be too low to detect.
>
>Just for inspiration - I recall one method used for high vacuum. The output
>from the apparatus pump is connected to a helium detector (I'm not sure how
>this one works, but that's not important for now). Then the apparatus is
>checked with a slowly flowing helium, comming out of a small tube. The
>helium stream is targeted at various places and when it strikes the leaking
>spot, it is sucked inside and consequently pumped out to the helium
>detector, which gives audible signal proportional to the helium
>concentration. Furthermore helium is lower viscosity (thinner) than air, so
>it leaks more.
>
>If the leak is big enough, maybe you could just measure the pump output
>flow and spray the suspicious places with helium. Hydrogen could be also
>used, since it is also low viscosity. Just don't smoke around when spraying
>with hydrogen ;-).
>
>One simple method of checking flow is the buble method used in gas
>chromatografy in the early days. Will describe if you find this
>interesting, but write direct, I don't read whole list, I only scan for
>interesting topics.
>
>Josef Hanzal
>
>
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