If it is a BB4 pump you have a piston pump, not rotary vane. Piston pumps are positive displacement and will in a tight system, if in good condition give you 25-27" vacuum. I ran a BB4 on 225 taps this year and when the leaks were in check I got 25-27" all season. It will likely handle 500 taps, but I don't have the CFM specs to verify. Do not try to run at speeds higher than suggested. For proper RPM check with member "Windy Acres", he likely knows the specs for that pump. It is old, but a much better pump than dairy rotary vane pumps.
I change the oil in mine every 2 weeks, and I use synthetic oil.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.