Basic geometry question

I must admit it is a strange question for a model engineering site .

Edited By Martin W on 11/01/2012 11:35:53

Hi there,

My question is an honest one – why would it be a spoof? Many thanks to those who troubled to reply. I have bought a small dive compressor that I intend to use for filling dive cylinders and also for my ACME patented instantaneous tyre inflator.

The former needs properly filtered air, the latter can make do with just dried air. So the 52 dia x 170 tall filter stack is filled with a combination of silica gel and activated carbon as standard. This has a limited life and is a pain to keep regenerating/renewing. So I thought if I filled the filter canister with stainless ball bearings (£12.50 per K on ebay), the moisture in the compressed air would condense on the balls and give me air dry enough for the tyre inflator. Opening the filter cylinder dump valve and leaving the filter on a radiator for a while should dry it out ready for the next time.

I did the calcs based on 100% packing density assuming firstly 4.76 spheres, then again assuming 4.76 cubes. I was slightly surprised to get figures between 6000 odd and 3000 odd. And I know that 3/16” is actually 4.7625 mm.

I’m concluding now that I’ll stick with the silica and carbon rather than blow £60 on ball bearings to find that it either doesn’t work, or that the pressure drop across the stack damages my filter casing.

Thanks again for the help,

Glyn