Following is a great guide for Vacuum Pumpers. Its taken with permission from the web site located at www.tigerpumping.com. His hosting costs are getting a bit much so please visit his site and look at the various vendors he has listed. Great Resource! 

In order to view this guide you need to have Acrobat Reader installed. 

You can download Adobe Acrobat Reader it from 

I might recommend that you download it to your computer, rather than viewing it online. To do so in Windows, right click on the file and choose save. The embedded web links should work, regardless. The file is about 6 Mb, so if you have a slow connection, it may take awhile.