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.
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
Bruce Meagher
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Re: Vacuum pump rebuild

Post by Bruce Meagher »

Thanks for the pictures Rex, and the data point with the small pit on your first motor.

I don't know what I was thinking last night. Clearly you can only remove a very small amount of material from the cylinder or rotor while still maintaining the oil seal at the top between the rotor and stator. We'll know more about the condition of the pump internals this weekend.

Bruce
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

Rex did a good job on the 1402 oil reservoir. I love that he noted the vacuum didn't improve all that much, if at all.

I have always said let the sleeping dog lie. I have two 1402's here. I rate them as one of the finest pumps ever made by anyone.

I bought my first one over 18 years ago. It pumped down with dirty oil to 15 microns. I drained the oil after a 1 hour run. It was a bit rusty and filthy as well. I reloaded TKO pure oil and ran for 3 hours. Drained and the oil was murky but cleanish. I finally reload with good belt drive oil and it pulled down to 5 microns. I never looked inside. At 5 microns it is a good pump.

TKO oil is flushing oil made specifically as a thin pump cleaning oil.

The second pump I picked up at a hamfest. I could see no oil in the pump at all. The drain plug yielded about a cup of grime and sludge that oozed out. I dare not try to hand rotate the pump pulley.

I mixed TKO 50:50 with Marvels Mystery oil and filled the pump. I let it set for 1 week, after which time I tried to turn the pump wheel and it broke loose from a locked condition fairly easily. I turned it by hand for several turns and was smooth. I ran the pump for only 5 minutes and then drained a pure rust colored ruby red oil. I reloaded this time with TKO and let the pump run for a full hour and the pressure was down to 20 microns. (Marvels Mystery oil has fractions that create vapor from that first fill.) I drained again and the oil came out only slighly rusty but without sludge. A final filling with real pump oil and the pump went to 10 microns. I ran it with this oil fill on and off for a week and on the final day it pulled to 12 microns.

One final drain had the oil fairly clear of rust and just a little light gray near the end of the draining, (sludge). A final last fill with oil and the pump pulled to between 5 and 8 microns. I have left this pump sitting for 8 years. About 6 weeks ago I used it to evacuate a discharge tube that I was testing and it pulled to 10 microns after 10 minutes of gas ballasting.

Two sleeping dogs restored with no peeky up their skirts to see what was really there. For my money if your old used pump gets down under 15 microns, your pump is good enough. A nice sludge lining that allows the system to pump to that level can be left in the oil reservoir. If you change your oil in heavy use as required, it will ultimately work its way out in the draining.

Richard Hull
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Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I took apart the pump this morning. The first picture is the pump. It is only three inches long but it does all the work. You can see the little coupler that attaches the motor to make the pump turn. The second picture is looking down at the pump. The third picture is the first stage and second stage split apart. The U shaped cutout is what connects the two stages together. The fourth picture is everything inside disassembled. I didn’t take the vanes out of the rotor yet. The last two pictures are the first and second stage chambers. They have some rust so the pump might not work well when I put it back together. I’m going to clean everything, and then put it all back together.

My dad is also going to help me learn how the pump works in more detail.

Tyler
Attachments
The pump and coupler
The pump and coupler
Top view of pump
Top view of pump
First and second stages split
First and second stages split
Pump disassembled
Pump disassembled
Second stage chamber
Second stage chamber
First stage chamber
First stage chamber
Rex Allers
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Re: Vacuum pump rebuild

Post by Rex Allers »

It looks better than one might have expected from the rust caked picture a few days back.

You might want to try electrolytic rust cleaning on the pump parts.

Hope there's still some life in it that you can save.
Rex Allers
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I used simple green to get the oil off the pump parts, and now they are in the electrolysis bucket. It’s a 5 gallon bucket with 1/3 cup of washing soda and 4 gallons of water. A 12V DC power supply is connected to 4 pieces or rebar. I hung the parts in the water from a metal bar. The bar is connected to the negative side of the power supply. I don’t really understand how it works, but it sure does remove the rust.
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IMG_0657.JPG
John Futter
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Re: Vacuum pump rebuild

Post by John Futter »

Tyler
your father has introduced you to the magic of reduction
in this case iron oxide is being reduced back to iron.
this process is used by vintage experts to reclaim old engine parts left out in the weather for 50 years or more.

Note to others if it is a saltwater corrosion you have to use a different electrolyte -- google it!!
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I finished cleaning all the pump parts. I have also been studying how the different parts fit together and make the pump work. I will post more about that after I have the pump running. Below are pictures of my progress. The first one is of the whole pump cleaned and ready to be assembled. The next four pictures show the pitting on the rotor and stator. The wire in the picture is 0.004” in diameter to help understand how big the damage is. The next three pictures are the pump being assembled. Next week I’m going to attach the motor and see how well it works.

Tyler
Attachments
Pump parts cleaned
Pump parts cleaned
Rotor pitting
Rotor pitting
Rotor pitting zoomed
Rotor pitting zoomed
Stator pitting
Stator pitting
Stator pitting zoomed
Stator pitting zoomed
Second stage assembled
Second stage assembled
First and second stages
First and second stages
Assembled pump ready to be attached
Assembled pump ready to be attached
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

In my previous posting in this thread about rebuilding my Trivac D16 I mentioned the damage caused by a split-pin holding the rotor to the main shaft that disintegrated in the pump. It was mostly to the stator walls, rotor sides, vanes and they were pretty deep since the pin was made of hardened steel(similar to your photo but not as distributed) .

Two things to note here however. My pump uses vanes on the rotor. This allowed me not to worry too much about how much metal I removed from the stator (photo in previous post) and second, as stated by the rebuild manual, scratches at the ends of the rotor or the center rear bearing will cause poor pump performance. To repair these areas I used Permatex cold weld or some metal epoxy with similar expansion coefficient and adherence. It is an epoxy with metallic filling. Cleaned with methanol (hot) and acetone. Waited two days after the epoxy and machined and sanded the ends smooth while keeping the original rotor thickness identical so the epoxy only filled the damaged area. As I mentioned it has been running perfectly for 10 years now since there are little contact there apart from the pump oil.

Same process with your pump might work for you, as long as there is no metal to metal contact with the rotor in those areas. Another option is plasma torch buildup as used in repairing car crankshafts and valve lobes. Your local machinist might be of help here and hone the stator cylinder for you. Same for the rotor.

Looking forward to seeing your progress.
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

I follow with great interest this adventure and love's labor into the attempt to restore a pump that under any reasonable and cogent examination would be instantly and unquestioningly consigned to the scrap metal pile.

If billed for labor at a mid-range figure for metal cleaning, electro-chemical activities and machining of $40.00 per hour, coupled with the supplies consumed would make the effort of saving this pump exceed the price for a brand new pump by two or three times!

It is also noted that if even only moderately successful, the "hands-on" knowledge gained and the extent of the effort involved in this attempt might well be priceless in that it will lead to successful future efforts when one is "up against the wall". The "hands-on imperative" drags one not only to greater mechanical prowess, but also to gained knowledge and advanced creativity and inventiveness as all of these skill sets are often pressed into service and even tested to their limit.

Again, this is a fascinating and heroic thread about the "doing".

Richard Hull
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richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

Quote Richard:
""It is also noted that if even only moderately successful, the "hands-on" knowledge gained and the extent of the effort involved in this attempt might well be priceless in that it will lead to successful future efforts""

Have to agree with Richard about this. After my rebuild success I have come across a few pump repairs and even a turbo pump bearing change with a lot more confidence and it was quite worthwhile. In addition the knowledge and tools acquired (that had to be paid for only once) but keep on being useful in the workshop quite often and have "repaid" themselves many time over, for pumps to dishwasher to car repairs etc...

Can't wait to see what performance you get out of it. And, if not to your liking, nothing prevents you to get in there again (should be much faster) to rectify the issue.

Note: should you get acceptable performance don't forget to change the oil after a while to get rid of impurities and metal bits before putting it in regular long term service.
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

Rich and Richard, thank you for your comments. So far I have only spent money on a minor rebuild kit, new motor bearings, power cable, and a few bolts. New vanes cost about $200 so I used the old ones. My dad and I decided we would use the pump to learn. He said the machining would be too hard for me, but we did not talk about using epoxy with metal. I just learned how to use a micrometer. I hope the pump will be ok for something.

Rich, I do not understand your comment. The picture of your stator looks like mine. Does your rotor not have vanes in it? How can you not worry about removing material from the stator? Below is a drawing of one stage of my pump. I will try to explain how I think my pump works later, but the rotor and stator create a seal at the top between the intake and exhaust ports. If I remove material from the stator or rotor the space at the top would get bigger and the oil would no longer seal the two sides. There are 12 areas that have to be sealed. Every edge on the box I have drawn at the bottom of the picture has to have a seal for the pump to work.

Tyler
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IMG_0750.JPG
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

""Rich, I do not understand your comment. The picture of your stator looks like mine. Does your rotor not have vanes in it? How can you not worry about removing material from the stator? Below is a drawing of one stage of my pump.""

Thanks for the drawing. A picture is worth a thousand words indeed. I know understand better how your pump in configured.

I attached a scan of the repair manual and a sketch I did to figure out how long to make the pin to attach to the main shaft. As you can see I have three vanes. They are free to move in the rotor slots and centrifugal force keeps them against the stator wall. If you look at the manual top picture you can see three volumes , "A" left from intake, bottom (B) fully expanded, right venting in the back wall bearing plate (C). Gas is picked up via the intake tube into an increasing large chamber (A) until sealed off by the second vane that forms a second expanding chamber (B). The rotation makes that volume smaller (C) and compresses the gas that escapes though the bearing plate on the side to the second stage. Note that the top 2 vanes takes care of the sealing between (A) and (C).Intake comes in at about 10 to 11 o'clock in the stator wall and exhaust at about 2 o'clock in the back wallplate going to the second stage that from view. In that geometry I do not have to worry too much about a top seal like yours and that is why I was not overly concerned in loosing a small bit of the wall by honing but more worried about the sealing bearing plates clearance on both ends.

The second stage was dirty but not damaged so I figured a slight loss in efficiency in the first stage might not be disastrous.
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notes008 (Medium).jpg
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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman »

Different Rich here. Hard to believe almost eight years have passed, since I worked with any vacuum pumps.

Tyler's drawing reminded me of a perplexing detail in my own scrounged pump, which I took apart for a different problem. This image illustrates the curiosity, and might also serve as a data point for smoothness.

We see that each vane tip touches the chamber wall at only one corner. For one vane it's the leading edge, and for the other vane it's the trailing edge. Had some previous owner assembled the pump with some part backwards?

Turned out, I had fooled myself. The vane tips are symmetric, and the angled contact is just an effect of the eccentric circular geometry. :-)

I wonder if minor pits at oil-sealing places could be mitigated by backing up the rotary pump exhaust with another vacuum pump, for example a little diaphragm pump. That would greatly reduce the "atmospheric" pressure trying to overcome the sealing oil's viscosity, surface tension, and wetting forces. Beware of rotary pump oil being sucked into the backing backing pump.
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Jerry Biehler
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Re: Vacuum pump rebuild

Post by Jerry Biehler »

At that point you are pretty much making the really slow equivalent of a booster pump, also known as a roots blower. They dont rely on good sealing between the lobes and the walls, there is no contact and no oil. They are there to massively move air.
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

That's right...Roots blowers are always the first mover and shaker on giant chambered systems. Then maybe a huge mechanical vacuum pump picks up when the bulk of the viscous flow regime is taken care of by the roots. Days and days are often required to get massive chambers down to the sub micron level. Once down they are kept down with a permanent running to the mechanical pumping system and the secondary deep pumping turbo.

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
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I finished putting everything back together. I attached three vacuum gauges to the intake port and then started the pump. After a few seconds the top gauge was at -29.5 Hg. The thermocouple gauge was at 65 millitorr. The pirani gauge was 49.5 millitorr. The first picture shows the pump running with the pressure gauges. After a few minutes something weird started happening. The pressure started going up and bouncing around. It went as high as 150 millitorr, but it was changing really fast. I started the pump a few times and it did the same thing.

Then something weirder happened. I put my hand over the exhaust port for a second and all of a sudden the pressure really dropped. When I removed my hand the pressure went up and started bouncing around again. I placed my hand on the exhaust port longer and the pirani gauge went as low at 11 millitorr. My dad and I are trying to figure out what might be causing this.

Here is a link to video. https://youtu.be/o6wUOpPbQJs

Tyler
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

If you can hit and maintain 11 millitorr, that would be a win and a most acceptable pump. Good luck in figuring all of this out.

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 »

Just a guess or two:

1)
Leak between the exhaust and the intake?
Can you devise a way to see if atm pressure overtakes an oil seal or a gasket seal or a bearing seal?
The fact that it is intermittent with plugging the exhaust and (I assume) once the pump is warmed up could be due to metal expansion or lower oil viscosity creating that leak. If there is a "pumping" action on the exhaust volume putting your hand on the port gradually lower the pressure (not atm anymore) and if done long enough it will equalise and go the other way to an equilibrium (assuming a better seal than your palm).

2)
again with oil viscosity lower at higher temperature and the pitted condition of the walls and vanes and side walls could it be a loss of pumping action with vane/wall leaking or vane bouncing? Increased pressure building up in the exhaust volume could minimise that behaviour due to the smaller pressure difference? A bit like a Roots pump that although leaky by design will be able to pump large volume of air but will struggle to reach a low vacuum by itself due to all the leaks in the lobes.

Can you easily try a thicker oil to test?

3)
electrical issue affecting the gauge. Pump not grounded, stray current, EMI etc... Try to just touch the pump near the thremocouple and see if it changes. Are these difference of pressure noticeable on the other gauge, if readable?

I am not an authority on vac pumps by any stretch. Perhaps someone on this forum can comment or perhaps you could contact the folks where you got the rebuild kit and they might have experience with that brand of pumps. I was impressed by Duniway support when I had questions doing mine with their kit.

Finally, looking at your setup. The thermocouple gauge is quite close to the intake and can be coated by oil mist that influences its accuracy. This can be cleaned with acetone in mild cases.
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I fixed my pump problem. I installed the wrong valve on the pump exhaust port. I used the metal valve. My dad emailed the company and the metal valve is for a different version. I needed to use the rubber piece with the spring. The pump also had a slow oil leak from the lip seal because I didn’t put it in far enough. I fixed these two things and then ran the pump for an hour. The pressure was 8 millitorr on the pirani gauge. This time the pressure did not change when I put my hand over the exhaust.

The next test is to run the pump for 24 hours and record the pressure. My dad is helping me write my first python program to record the pressure on my PC.

Tyler
Attachments
Exhaust valve
Exhaust valve
Lip seal not in far enough
Lip seal not in far enough
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

Congrats!
If you click with Python there is a very good online course from MIT via the Edx program (assuming you have time).
I would not leave the thermocouple sensor as shown in your previous photo for a 24 h run. Pirani probably OK. I am sure Richard would know.

From your valve geometry was it because the metal valve was leaking too much atmospheric pressure in the internal exhaust port at the exit of the pump?
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