GRAEME SMITH                         email: grysmith@freenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.


On Wed, 30 Jun 1999, Peter van Hoof wrote:

> for deep vacuum applications Nx10-3 bar or so it is common to look for leaks
> with helium gas (small molecule so penetrates easy) and a helium detector at
> the output of the first stage pump (turbo,cryo etc)
>
> in mid range vacuum applications reverting to compressed air and soapwater
> might actually work
>
> in case you wish to try to find leaks with a microphone, consider this, most
> of the air vibration might be sucked into the vacuum.
>
While this is undoubtedly true, my admittedly limited experience with
vacuum leaks, hints that it is not likely to make a difference, since the
vibrations set up in the surrounding material, will be as detectable as
the original leak. Since what you really want is an indication of where
the leak is.... your ideal test rig, is to have the detector, in your
hand, rather than some distance away.

Perhaps there are limits to this technology, on the size of the leak that
can be detected, certainly I can't claim to be an expert, but the
alternative is not an inexpensive circuit that can be mass produced, and
carried in a pocket, if only because it is difficult to carry a large
bottle of helium in your pocket. [G]

                                GREY