I first started reading up on this about a year and a half ago, If you truly want to do this like the big boys, Your going to need to do a few things
1st, you need to build a containment vessel that will go from maximum vacuum to 3500 psi, which can easily be done with thick wall 3" black pipe which has a burst strength of around 10.000 psi, nice cushy safety margin right? As mentioned above some guy built his out of a howitzer barrel which is insane overkill, but cool none the less, bursting strength on that barrel is around 60,000 psi
2nd, you will need to generate 3500 psi easily done with a scuba tank compressor
3rd, you will need some safety equipment in the form of a containment area (block wall) and a containment vessel, My idea buy a 24" and a 12' sonotubes fill the gap between with concrete, then fashion a steel lid held down with chains, underneath this you will need to create an escape route for the compressed air in case of containment vessel failure, I figure a 4 inch pipe with a couple of elbows should do the trick, pointed in a safe direction of course ;0)
4th, when compressing air you generate a lot of heat, So you will need to fashion an intercooler, Other wise your stabilizing fluid will set up, I think a simple water jacket over the inlet tube will work, borrowed that idea from a still design I ran across one time, Cooling compressed air will cause condensation, so you will need to fashion a catch basin inline after the water jacket
5th, you will need to incorporate the vacuum system into this mess, doesn't seem like a biggie ;0)
6th and final step, Cycle this setup 3 or 4 times starting with vacuum
