erubin,

Don't worry, I know you're not "picking on us." In fact you're bringing to light some good discussion.

If the venturi pump will indeed pull 27.8" then it will indeed work. I think the reason I wouldn't like using one is the fact that I like to evacuate overnight when I can. I can't imagine running my compressor all night long.

You quoted something I said in 2002 about an a/c compressor converted to a vacuum pump. I must have misstated. It was an ol refrigerator vacuum pump. It came out of a refrigerator that my Dad bought new in about 1954. The reason it works without circulation is that there is oil in the bottom of it. It would probably still be working except I stored it open in my shop which gets very humid. It finally gave up.

Yes 32" is theoretically impossible. Most gauges are marginally accurate on the vacuum side.

Good luck with your project,