Most of this comes from about 15 years back, when I was dating a
physics grad student. I helped her rebuild a number of Welch pumps,
and ended up with about half a dozen of the ones nobody wanted.
So, what I meant by rotaries are the classic Welch duo-seals, like
the 1405, 1402, 1397, 8821, etc. Big huge disk set eccentrically
within a cylindrical chamber. Two opposed wiper blades, spring
loaded so that they ‘wipe’ along the walls of the chamber, forming a
self adjusting seal against the wall of the pump chamber.
What I meant by vane pumps are more like tubo pumps, now that I
think of it. I’ve never gutted one of these, so this is going on
what I was told. As I understood it, these pumps work by way of a
spinning rotor of lots of little blades that essentially slings the
gas out by centripetal force as the atoms impact the whirling
blades. Never gave it a whole lot of thought, but now that I do, I’m
a little puzzled about what the oil does in these things. Thinking
about it now, I’d expect it to get in the way. Anyway, given how
they work, they can move a lot more gas, a lot faster than a
duo-seal style pump, but have trouble with ultimate vacuum. More of
a roughing pump. (even more of a rougher than the Welches.) From
discussions we had at the time, the vane style pumps needed lighter
oil with less lubricant in it than the Welches did. Unfortunately,
all I’ve got around here are Welches, so I don’t have an example of
a vane pump to give you a model number. Let me check in the
vacu-cast machine out at school, and I’ll see what kind of pump it
has, and maybe that’ll help give a handle on what I’m talking about.
(It’ll take about 2 weeks, we’re on break.)
I’m not totally making this up, really.