I show the parts I had to modify to turn a small 12 volt compressor into a vacuum pump. No, just running a compressor backwards won't work! However, on a larger piston compressor, you can bleed the air tank down to zero, and leave the tank outlet open, then connect a strong hose to the inlet of the compressor, and it will become a vacuum pump. Things were not so easy to modify on the little compressor, as there was nothing to connect to on the inlet side, so I had to build it. Also, it doesn't use piston rings, so I had to figure a way around that by reversing the piston, so the cup ring worked on the suction stroke.
