Virtual vacuum leaks

I have a really good quote about vacuum leaks, and thought that I had blown the chance to use it, already having fixed one leak. Today I tried to restart the Stern-Gerlach experiment, and found that it had a huge leak in it. There was a very good reason for this: I had attached a light to the vacuum system to check whether it was aligned properly. This light was built in to what looks like a leak-tight metal plate, but which actually has a huge hole in it.

The picture below shows what happened: the air which was pumped out by the pump was continuously replaced by the air coming in through the leak. Now the funny thing is that the leak could only be heard by listening to the bellows, which I drew as being the zig-zaggy thing. At this point you could hear a hissing sound. This hissing sound couldn't be heard at the point where the air came in, only when it passed through the bellows.



After a couple of hours, and after installing a spare bellows which made exactly the same noise, I worked out what was wrong, and removed the piece with the hole in. For a while I was annoyed, but then I realised that I may have created a new musical instrument: the leakophone. Presumably by varying the tension in the bellows you could create a whole range of hissing sounds with various tones. Add a couple more bellows and you could play a lovely tune. Before I forget, that quote, stolen from R.K. Fitch who claims that it was a student's answer to an exam question.

The essential components of a high vacuum system are a rotary pump, a diffusion pump, and a leak