Sterlingfluidsystem has a very good site indeed. Also check the website of Dekker.
Here is a link for the selection of liquid ring vacuum pumps and I found it to be the best(moreover it is very handy). Enjoy downloading and reading it.
PS: You can't get to this link even from sterling's website(in this format). I reckon it is an acheivement to my searching skills
Regards,
Believe it or not : A Neutrino is so mass less(and electrically neutral) that, a conservative estimate states, it can pass through a 50 light year thick lead block.