I have an old montgomery wards seperator, it works wonderfully. They are a little fussy to operate, they must be spinning at exactly the right speed in order to operate properly. I had a full size one that would hold 5 gallons in the bowl, It was very worn and very fussy to operate. Every time I used it I had milk everywhere. We found a table top model at a flea market in pieces. I sat down on the ground and put it back together. DH thought I was crazy, I told him it was missing a few parts that we may be able to find. We got it for $45 and the guy wanted $80 for it. After we had it in the car I told him that it wasn't missing a thing, didn't even feel guilty about it. That guy ddin't even know what it was.
They take a lot of work to clean up. So much that I won't even attempt it with less than 4 gallons at a time.
I don't know if there are any instructions out there on how to use one. I learned from my mom, and it would be very hard to try to explain. I wouldn't encourage anyone to try to buy an old one to use if you didn't already know anything about it.