One last try of the message with just the text place holders I inserted for the images. No jpg images uploaded or inserted this time.
I would think if you open the actual pump chambers and find nasty surfaces, that your question about honing the inside of the stator or smoothing the outside of the rotor would be limited to very small amounts.
I think all these pumps require a very close tolerance between the rotor and stator that is set in the narrow region of the stator between the input and exhaust ports. This very small gap with the pump oil forms an effective gas seal that must be good if the pump is to work well at all. If you take even a mil or two out of that gap, the pump may not work well at all.
On the other hand, I have some experience with crapish pumps that were still useful.
--- Pump 1 ---
I bought an Edwards E2M12 from eBay -- "Like new vacuum pump in good working order. Pumps down with no issues" -- partially because the seller was local. I picked it up locally and was a bit concerned when I found myself in a semi-commercial-looking garage setting. Got it home and tested. First pass: 15 Torr! Ye gads -- that sucks in general but not very much in the vacuum sense.
More trying over a day or two, eventually it seized up.
I eventually figured out that the pump was used to extract air from fiberglass molding processes. This seems to be a common cause of destruction of pumps that find themselves to be sold on eBay. They suck abrasive glass fibers and plastic resins.
Talked with seller and eventually he agreed to refund most of what I paid and I used that to buy a major rebuild kit with vanes. Here are a few pictures from that process.
Some schmutz I found early but this is actually external to the pump unit so not too worrying.
Next a pic of the inside.
Not too bad at first look but that vertical rod is a fine mesh filter. It is totally encased in the crap that was running through the pump.
One of the rotor shafts shows a bit of scoring at its bearing surface.
Not terribly bad. Nothing sensible to be done about this so I just ignored it.
Now the worst of pump internals, probably from whatever got loose and jammed to seize the pump while I was testing.
The stator.
There's that one nasty small gouge from something that got into the pump. You can also see finer scoring lines around most of the surface. I also marked the region between the input and output ports where the tolerance between the stator and rotor surfaces must be very close to seal gas with the pump oil.
Here's the rotor.
A nasty mark corresponding to to the one on the stator. No idea what happened to get it to cause a dent down into the vane groove but there it is. You can also see minor scoring across the whole surface.
So I did the whole rebuild, being sure to clean gunk out of all the passages. I did a little bit of fine sanding on the rotor and stator, mostly just to be sure there were no high spots. All the valve parts, gaskets, and o-rings where replaced.
At the end of the rebuild this pump seems to run well and I am getting about 14 mTorr from this pump. Quite usable.
--- Pump 2 ---
I bought an old Welch Duoseal 1402 belt drive pump from Greg Courville on this forum. Checked it out and pump was working well. I measured about 5 mTorr vacuum. (I used a less trustworthy gauge then than my recent measurements so could be off my a couple.)
This is a 1402 with the top ballast valve and keyhole sight windows so must be very old. Maybe 70's? Maybe earlier?
I decide to do some cleanup. First I made new hard rubber feet for the base. Then I cleaned all the externals. No signs of oil leaks. The sight windows for oil level were dirty enough on inside that it was hard to easily see the oil level. I drained a little oil and got some crud coming out. I decided to open the case and do some cleaning.
Here's what I found.
Kind of yucky. I decided to clean up what I could without opening the pump unit, that seemed to be working fine.
I took off the external valve parts and cleaned them. Here's the pump module after cleaning.
The valve parts are removed and wooden dowels are protecting the pump ports while I was cleaning.
Here's the case inside after I did lots of cleaning.
Much sludge scraped out then scoured cleaner. The inside of the oil level sight windows was one of the harder parts to clean. I also lightly milled the gasket surface flat. (I'll skip the details.) Years of people jabbing stuck gasket off had left it kind of not too flat.
So put back together it's nice and clean. With my MKS 901P sensor (I have 3 and trust them) I see about
3 mTorr. My best pump.
All the clean up work didn't change the good vacuum it started with much, if at all, but it makes it look better and should help it keep working well into the future.
--- Pump 3 ---
Just a few days ago I bought Ian's Edwards RV5 pump. He measured good vacuum, about 4 mTorr, and I confirmed the same when I got it home. I let it run for a half hour or so until it got pretty warm and the vacuum came up to about 6 mTorr, but that's still great.
It is very quiet while running too.
It looked good but I spent a day cleaning it all externally and it looks almost new again. In the process, removing side covers and such, I saw no bad signs like oil leaks or anything. From parts in the electronics of the motor start, it looks to be probably from about 1995. So probably more than 20 years old.
(But the Welch 1402 might be about 40 or more years old.)
--- Conclusions ---
The pump you have could be saveable if the insides are not bad.
If they are bad, I think most rotary pumps can't tolerate more than a tiny amount of surface removal.
A pretty clean looking pump can have major problems from contamination, but I was able to bring it back to fairly good performance.
A perfectly working pump can have a good bit of crap inside.
--- My thoughts ---
I'd clean enough to open up the pump module more easily and then see how good or bad the rotors and stators look. Also any shafts and bearing surfaces.
My E2M12 shows that slightly damaged pump internals can still make a useful pump. But I wouldn't expect very much damage could be recovered from.
The Welch pump shows that some significant crap inside that can be there and the pump still works fine.
A nice clean 20 year old pump is a lot easier than fixing or refurbishing old pumps.