If you are interested in sterile filtration, here is a very informative site:
To remove yeast, you want a 0.5 micron filter.
Note rule #1:
"For Sub Micronic FIltration always use a plug in or plug on style."
That means do not use a standard DOE (double-open end) filter to remove yeast. I wish I knew this 6 months ago. I bought a Pentek housing and a Flowmax filter... and experienced leaks and poor seals.
Note that all of the commercially-offered homebrew filter setups use DOE filters and housings.
Now I have a 222 O-ring filter and a nice polypropylene housing; no leaks. Both are from McMaster Carr for $90 total. My next upgrade will be to a Polyethersuphone membrane filter.
Also, many beer filter websites would have you believe that you must filter in stages. Not true. You can filter a keg of brew in one pass, through a 0.5 micron filter with no problems. Takes about 15 minutes, with 15 PSI on the supply side and a pressure relief set at 10 PSI on the receiving keg (5 PSI differential) - these values are arbitrary.