Fxing a Welch vacuum pump

Our Welch 1400 vacuum pump at work has seized up. As our boss is on vacation and left me in charge (why we still aren’t sure) disassembling it seemed like a good idea. We got off most of the parts, but the shaft is stuck in the main assembly, which will not come apart even though we removed all of the bolts and screws. Does anyone have any advice? We are currently stuck up a creek without a paddle, as it’s said, as we can’t order parts until the boss returned, but any tricks of the trade would be nice. Oh, it seized do to the fact that the people I work with are dumb and suck orgaincs and corrosives through it without proper trapping.

What exactly is the shaft stuck in? What parts are we talking about when you say “we got off most of the parts?” I’ll probably be able to help if you can describe the situation as it is now a little better.

I’m assuming you’ve removed the belt(s), unbolted the vacuum module from the base, and removed the outer oil casing, is this correct? Have you taken the module apart yet? Note that in some vacuum pump designs, the shaft is mated to one of the the rotors at the factory and shouldn’t necessarily come off unless there’s a problem with the shaft or the rotor it’s attached to.

Yeah, most people don’t care enough about their vacuum pumps before they break. Cold traps (CO2 or N2(l)) are always a good idea, but you know that. Regular oil changes are also necessary, especially if the oil changes color or has solid particles in it, but you probably already know that too. :slight_smile:

Btw, I’ve successfully rebuilt Welch, HyVac/Cenco, Leybold, and Alcatel vacuum pumps before, so don’t hesitate with the details, and hopefully I’ll be able to help.

Basics 7:Vacuum Pump Repair


Sorry about being not too terribly discriptive. My dad’s an engineer and we all explain technical issues using words like thingy and duhicky and all know what each other means. Plus I’m not well versed in pump lingo. The belts, rotor and this ring have been removed from the back of the main module. We need to get the main module, which has the shaft stuck in it, appart, to clean it and get the shaft turning again. It seems as though the two halves of the main module should come apart, as all of the bolts appear to be out, but some force greater than us is keeping it together. I’m considering bringing it home where we have much better tools (damn state schools, no money for anything worth while), but any advice you have I would be very greatful for, as would my lab partner, as he has named the pump Torri. It’s the only one we have that wasn’t overly tempremental. Anyhow, that’s if you have advice and even if not, that’s for trying to help me.

Here is a detailed pdf exploded diagram schematic of the Welch 1400

Thanks, astro.

gfloyd, if you look at astro’s link, parts 19, 42, 25, 36, and 32 make up the module. Can you not get 19&42 off 25? Or 36&32 off 25? Or both? You said the pump’s seized. It’s possible you’ve got corroded crap sticking the parts together. With your engineering background, you’ll probably like my advice…beat the shit out of it with a hammer. No, don’t really beat the shit out of it, but you may need to ‘persuade’ the module parts on either side of the center plate to come loose. If you’ve got a rubber mallet try that, otherwise a metal one will do, but try putting a block of wood in between the hammer and pump so you’re not hitting metal on metal. Tap the module all the way around; pretend you’re trying to open a pickle bottle by banging it on the counter. The outside of these parts isn’t the most important part, it’s the finely machined surfaces on the inside and in between the module plates that shouldn’t be damaged. DO NOT pry these things apart with a screwdriver or something…if you scratch or groove the surface in between, say, 19 and 42, and if you get the pump fixed and put back together, it won’t pull as strong of a vacuum, since the scratches introduce a vacuum leak.

See if you can get everything taken apart and report back. Don’t bother ordering a module repair kit until you can inspect the innards to determine whether it’s worth the time and money repairing the pump. Allowing organics into the pump lets them react with the oil and the cast iron to rust the pump. The rust flakes off and small pieces of metal get into the workings, creating grooves that allow vacuum to leak. 2-stage rotary vane pumps (what you’ve got) are expensive, but you should be able to find refurbished ones that are cheaper and will work fine if you can’t fix Torri. If your lab partner likes your pump enough to give it a cute name, perhaps he should like it enough to treat it well.

If you’ve got a machine shop at school, I suggest you get friendly with them. Mine here at the University of Oregon has been indispensable with the right tools and mechanical know-how.

Thanks, I’ll give that a try. And it’s our third lab mate that doens’t understand trapping.

Make him understand. Use the aforementioned hammer. :slight_smile:

Or try not letting him use the pump after it’s fixed.

Good luck, and keep me posted.

Make him/her tear down the other pump(s). :smiley: I’ve had to tear down an Alcatel pump because someone didn’t turn on the trap refrigerator. When you do get everything apart, clean well. I vacuum-dried everything in the bowl of a second concentrator we have. I seem to remember having stuck parts as well, and I think I removed the vane rotor and vanes (37/20 and 40 in the diagram) to get everything un-stuck.

Jack-of-all maintenance
and Master of none

I finally got it apart. Lots of brute force and a rubber mallet. Thanks for the advice, I think I’m well on my way. It seems that pyrolized oil was my main problem, and that can all be cleaned out. I have it soaking in solvent at current, to give it the toothbrush treatment soon.

Excellent. I think the best solvents for cleaning are acetone or ethanol, followed by either an air dry or (even better, and quicker) drying in a vacuum oven if you’ve got one.

If you don’t know already where to get a major module repair kit, I suggest PrecisionPlus.com. I alaso suggest you get a manual for your pump if you don’t have one already.

Keep us posted if you’ve got any problems putting it back together.