For the shop.
2 or 3 cylinder piston compressor, belt drive 10 to 13CFM. For tyres you don't need much of a reservoir but for much else, (including painting) the bigger the better.
For the van.
Size E bottle of dry nitrogen with a welding regulator.
There's a vast quantity of shite out there, to the point where there's hardly a good quality rig to be found, don't expect to buy anything worth owning for a couple of hundred.
Bookmarks