In the past year I have been using three different vacuum chambers and three different vacuum pumps. I thought I would give a little comparison.
I only used this one a few times. It is quite small. 4" diameter PVC coupler I believe. The vacuum pump is an Air Cadet Model 420-1901. It is a single stage pump and does not quite pull a full vacuum. I was getting about 26 inches of mercury.
This one is the one that I have been using most of the time. A coworker of mine built this a few years ago and my work has used it ever since. The pump is a Robinair VacuMaster 2 Stage Pump, Model 15500, 5 CFM. This pump works great. It is very powerful and 5 CFM is very fast. Even with this 12" diameter vacuum chamber it only takes a little over a minute to get to full vacuum. One thing I will say about this pump is that it is quite heavy and costs over $200.
I named this vacuum chamber baby bear because the first one was too small, and the second one was too big. This one is just right. Actually, the other two were not my to own and I was tired of borrowing them from my work. I was having to carry the Big Boy back and forth from work. UGH.
The pump is a Pittsburgh Tools, 3 CFM two stage pump. I got this from harbor freight. It is a little smaller pump than the RobinAir so it would take longer to pull a vacuum on the same size chamber. But since this chamber is smaller than the other one it actually takes less time to reach full vacuum.
The only think I don't like about this pump is that it make some oil vapor. I have only used it a few times so far and at first I thought something must be wrong. I did a little research and is sounds like all oil vacuum pumps do this. But the RobinAir vacuum pump does not seem to do this. I read that these pumps tend to make more vapor when they are brand new. I will post an update after I use it for a little bit. Anyone have experience with this?
Here is a link to a video of someone else's pump doing the same thing.