Vacuum pump rebuild

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Tyler Meagher
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Vacuum pump rebuild

Post by Tyler Meagher »

Hi,

I have started taking apart my vacuum pump. It is a Pfeiffer DUO 1.5 A. I removed the motor from the pump and the motor was complete stuck. I didn’t know it was completely rusted over inside until I started taking it apart. It looks like the shaft seal leaked and water and oil got inside the motor. My dad said the motor can probably be fixed with a little cleaning and some new bearings. We had to make a special tool to remove the motor housing bolts because they didn’t have a standard bolt head. Below are pictures of the pump and the disassembled motor.

Tyler
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Adam Binns
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Re: Vacuum pump rebuild

Post by Adam Binns »

please keep us up to date on the results as I have always avoided broken parts due to lack of experience with repairing them and would like to see someone repair vacuum parts.
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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman »

Yuck! I'm sure the motor will feel much better after some TLC from you.

Rust-encrusted steel tools clean up amazingly well with an overnight soak in plain vinegar.
I've never tried that with electric motor parts, but imagine it would be no problem on a stator.
For armatures, pay attention to side effects from galvanic current between dissimilar metals in contact.

To get residual vinegar out of nooks and crannies, and maybe porous insulators, plain water ought to do the job. It's safe, cheap, and available under pressure from garden hoses.
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Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

Adam, the pump I’m rebuilding is the same pump Andrew Seltzman rebuilt: viewtopic.php?f=10&t=9214&p=62499&hilit ... duo#p62499. He provided tons of photos and the service manual so I have a good guide to follow.

Rich, thanks for the advice. This morning I cleaned the parts with simple green and scotch bright pads. I then put the stator in a bucket of vinegar. Tomorrow I’ll see how it turns out. I also ordered two new bearings. Next weekend I will reassemble the motor.
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I finished rebuilding the motor. There were 5 hard parts.

1) We didn’t have the correct punch to remove the roll pin holding the fan on the shaft. We used a small nail instead.
2) The bolts holding motor together had a special top and my dad had to make a custom tool for me to remove the bolts.
3) There was a snap ring holding the front housing. It was hard to get off.
4) The pump coupler needed a special tool to remove, and we broke the plastic and magnetic ring when removing it. I’ll post more about that later.
5) Removing the bearings was tough for me and needed my dad’s help.

The first picture is the motor completely disassemble and cleaned. I used simple green and scotch brite pads to clean everything. I tried Rich’s suggestion soaking the stator in vinegar overnight. It removed some of the rust but I used 400 grit sandpaper on the metal inside to remove the rest. I put the rotor in a drill and used sandpaper to clean it up more. I also used the sandblaster on a few parts for fun.

The second picture is cooling the rotor shaft with dry ice. I heated the bearings with the heat gun and cooled the shaft with dry ice to make them go on easier.

The last picture is the fully assembled motor.
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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman »

Looks very nice, Tyler. Does it run when you plug it in? :-)

I just did a vinegar soak on some motor parts myself, for the first time, and on a big old screw extractor. The rotor sections are from my friend Tom. They appear to be of identical design, except for a mysterious difference in the twist direction.
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Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

Thank you. Yes, it runs when I plug it in. My dad wants me to run some more tests before I connect the motor to the pump. I will post about the those tests soon. In your picture I’m not sure why the twists would go in opposite directions.
Jerry Biehler
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Re: Vacuum pump rebuild

Post by Jerry Biehler »

It's usually a good idea to put a megger on the windings to check for leakage after a motor has been in that state.

This is also a good use for electrolytic rust removal. I dont like using acids no matter how benign around stuff like this.
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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman »

Don't want to hijack Tyler's thread, but my own motor-part-cleanup experiment needs an "after" picture.
The red object, included for scale, is a deformed M&M.
The metal parts got a vinegar soak and, I admit, some wire brushing. Armature bearing on the left was protected with petroleum jelly. Commutator was only half submerged. High water level was visible before polishing, where the brass surface had been de-zincified.

I haven't yet meggered the armature winding, but want to. That part was fished out of an e-waste bin, and isn't expected ever to run again. Unless it's re-animated by un-natural methods, for a "ball bearing motor" demonstration. :-)
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Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I got my first piece of test equipment. It’s a Fluke Digital Multimeter. This is the first time I’ve ever measured anything with electricity. I'm just learning about some of the test we ran, and I don’t have a good understanding of the meaning of each test yet.

I performed 6 test:

1) The resistance through the coil windings was 4.9 ohms. This measured the same before and after cleaning.
2) The resistance from the coil leads to chassis was open. OL displayed on the DMM.
3) The voltage was 121.4 volts AC when I plugged it in.
4) The current was 2.25 amps running the motor with no load.
5) The motor ran at 3568 RPM (revolutions per minute) with no load.
6) I didn’t have access to a megger meter to measure the insulation leakage, but we used a high voltage power supply to generate 500 volts DC across the coils and ground. I then measured if there was any leakage current with another meter. See picture below.

I'm currently measuring the mechanical horse power of the motor and computing the motor efficiency. I will have another update soon.
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Jerry Biehler
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Re: Vacuum pump rebuild

Post by Jerry Biehler »

Other than megging it and current the rest of the tests are not important. Put it together and get it working.
Bruce Meagher
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Re: Vacuum pump rebuild

Post by Bruce Meagher »

Patience you must have, my old Padawan.

The motor is complete. In fact, Tyler just finished making some measurements with the Prony brake we assembled. Next, he has to cracked open the pump side and try to get it back into a usable state. Given the current pace he's still a few weeks/months away from his first vacuum test.

BTW, I respectfully disagree that the other tests are not important. For the young folks (and old folks too) I think the fusor journey is about getting some practical hands on experience in a number of diverse areas. Tests and measurements are key elements of that experience. I have a half dozen working pumps, but why pass up an opportunity to look under the hood to gain a little better understanding of how they work.

Bruce
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

My dad and I built a Prony brake to measure the horsepower of the motor. We used this article:

http://chestofbooks.com/crafts/popular- ... otors.html

The first picture is the Prony brake setup. The second picture is measuring the input power and the mechanical horsepower. The third picture is a graph of motor efficiency vs measured horsepower. The forth picture is the first look inside of the pump. It looks much worse than the motor.
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John Futter
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Re: Vacuum pump rebuild

Post by John Futter »

I was surprised at how bad the motor efficiency was, but then I realised you are not measuring the phase agle of the current vs voltage.
So the actual power will be alot less due to current and voltage not being in phase.
analog devices make some brilliant metering chips ADE7751 that are simple to setup and although designed for kW/Hr meters some have an analog output (CF) of instantaneous power as well as the watthour pulse output
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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman »

Good catch, John. The exercise is simpler with DC motors.

Compliments to the Meaghers on the Prony brake. Never seen one like that for real. Once I ad-libbed a motor efficiency demo, using an analog "true wattmeter" and a brake made of wood, shaped like:
brake2.JPG
The brake collar tightness on motor shaft was adjusted with a screw and wingnut. Soon the shaft got hot, the wood began to smoke, and I bet the friction changed. I guess we could figure the mechanical power from torque x rotation rate, or from matching the amount of smoke when the brake is clamped onto a soldering iron. :-)

It being break time, I whipped up an AC phase angle demo in Excel instead of finding one on the Internet. Simple arithmetic instead of trigonometry and calculus, for Tyler's benefit.

It shows instantaneous voltage, current, and power every 10 degrees for 2 whole cycles. Voltage and current are signed values, but when they are both negative their product P = V * I is still positive. It peaks at 240 watts in each half cycle, and averages out to 120 watts.
pf0.JPG

In this demo the sinusoid data points are computed from the control knob values entered in blue cells.
The values in Average and RMS boxes to the left are computed from the same numbers that are charted.

When current has same intensity, but lags voltage by 40 degrees, the average power is down to 92 watts. At some instants the power is negative.
pf40.JPG
Ooh, the forum let me post an Excel file. See what happens when the lagging current phase is set to 80 degrees (unloaded motor, perhaps), or negative angles (a capacitive load), or near 180 degrees (an alternator with resistive load, or a wattmeter with I or V connection made backwards).
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Bruce Meagher
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Re: Vacuum pump rebuild

Post by Bruce Meagher »

Oops, my mistake! John, thanks for pointing out the error. I was trying to keep the exercise really simple, but that doesn’t work when you're doing it wrong! Rich, thanks for the spreadsheet and explanation. We'll spend some time talking about it, and re-run the experiment correctly when we have the proper measurement setup. In hindsight this is probably a little advance for a first look at electricity, but is a great example of why it's important to have other people review what you're doing.

Bruce
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Re: Vacuum pump rebuild

Post by John Futter »

Bruce, Rich, & Tyler

Sorry to rain on the parade, but Tyler now has to learn something that most EE's only get very late in the course.
It reminds me of my youth when with little or should I say no knowledge I thought I could light a flouro tube using a magneto a battey for the tube filaments and direct connect to the 230 volt mains.
Never the less the resulting explosion and glass going everywhere except on me (read very lucky) put me off playing with mains until I learnt how they use inductive ballasts to limit tube current--- much later in life.

So now we have introduced power factor. Tyler I hope your maths is strong.

But first make the vac pump look as good as the motor!!
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

Ugh.....That photo of the guts of the pump is typical of a pump that pumped a lot of moist air for a long time (months/years) with no oil change and then stored for years. It represents what is usually a pump's death and an indication that a new pump is a good idea.

Fighting back from situations like this can be fun, instructive, expensive and often not worth the effort. All the very best in this resurrection effort.
Sometimes it looks far worse than it is....Other times, it is far worse than it looks.

Richard Hull
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The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Jerry Biehler
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Re: Vacuum pump rebuild

Post by Jerry Biehler »

Yep, unbolt the pump and check the rotor and stator. If there is ANY pitting the pump is scrap. That probably should have been the first thing that was done.
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

I didn't want to say it, but Jerry is right on. #1 check out what really makes the vacuum. A nice, pretty, clean, smooth running motor married to it's special pump shell never makes a vacuum.

This is why I love belt drive pumps. Quiet running and separate unit pump and motor. The pump system doesn't have to have its special motor working at the same time as its pump. Any motor will work a belt drive pump..........and the motor will power any pump housing.

Any pump housing containing a pitted rotor, damaged blades or especially a pitted internal round housing is typically junk yard bound. How do you know this without opening the case?? If it is direct drive and the motor won't run, you will never know until you inspect it.

With a belt drive, if the motor runs and the pump turns you can vacuum test the system.

I would not hold out much hope for that rusty mass in your image.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

I do agree with Richard's and Jerry's views here. But, if you are in for a hero experiment, in particular after rebuilding the motor, here is what I ended up doing to mine.

When I got my Trivac D16AC pump it was jammed. Not quite as bad as yours in appearance inside but it had been used to pump silicone for molds...
The roll-pin on the center shaft driving the vanes holder had broken and the pin remnants had scored the inside walls and also chipped the vanes. I was able to restore the outer surface for the vanes using a flex car cylinder hone (smallest size I found). Started with a coarse one and went directly to the finish grade. That left a nice crosshatch finish that would bed in the new vanes.

While in there, I used a Duniway major rebuild kit. Fill with oil, dump, second fill and 5 x 10^-3 t and steady for the past 10 years or so.
Its lots of work but doable depending on how stubborn you are.

Worth it for kicks on your own time but not otherwise. I can post photos of the rebuild should you like.
Good luck with it.
PC272478 (Medium).JPG

=^,^=
Bruce Meagher
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Re: Vacuum pump rebuild

Post by Bruce Meagher »

I agree that normally you wouldn’t give this pump a second look. There are tons of vacuum pumps available on the second hand market in great shape that require little to no work. Add oil and go. Is this pump destined for the scrap yard? Potentially, but honestly it does not matter.

I fully expect a pitted mess when we crack the pump apart (hopefully soon)!

What level of vacuum could one achieve with “ANY” pitting? What about a lot of pitting? I don’t know the answers but this sounds like an interesting experiment. The vanes have significant travel. Can one remove 0.030” by boring and/or honing the cylinder to revive this sucker with little performance losses? The sides walls will probably have issues as well. What are the options to fix this… Boring, honing, facing, surface grinding, lapping, and the measurements of these processes are whole new areas to potentially explore. My hope is we gain a little practical knowledge about how two stage mechanical pumps work and maybe a few other things while we’re at it.

Rich, I’d love to see the pictures from your rebuild.

Bruce
Rex Allers
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Re: Vacuum pump rebuild

Post by Rex Allers »

Quick short test after three long reply attempts failed.

Please ignore.
Rex Allers
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Re: Vacuum pump rebuild

Post by Rex Allers »

Fifth try failed.

7 pictures ~100K each uploaded and inserted into fairly long post. Previewed the post and all looked ok. Click the submit button and after a few seconds connection is reset. No post. I open browser window again to forum and I'm still logged in but my post is vaporized.

Must be something in my post that the forum system doesn't like. Is there a file upload number limit per post?

I give up. Thought it might be a little helpful.

These short ones seem ok.
Rex Allers
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Re: Vacuum pump rebuild

Post by Rex Allers »

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.
em extern yuck.jpg
Some schmutz I found early but this is actually external to the pump unit so not too worrying.

Next a pic of the inside.
em inside.jpg
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.
em shaft abuse.jpg
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.
em stator scoring.jpg
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.
em rotor gouge.jpg
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.
01 Case Open Sludge 1.jpg
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.
17 Clean Pump Inside.jpg
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.
21 Cleaned Case 2.jpg
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.
Rex Allers
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