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.
Rex Allers
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Re: Vacuum pump rebuild

Post by Rex Allers » Sun Apr 22, 2018 11:47 pm

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 » Tue Apr 24, 2018 2:52 am

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 » Tue Apr 24, 2018 6:44 am

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 » Sun May 06, 2018 2:12 am

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.JPG
Pump parts cleaned
rotor pitting.JPG
Rotor pitting
rotor pit zoom.JPG
Rotor pitting zoomed
stator pitting.JPG
Stator pitting
stator pit zoom.JPG
Stator pitting zoomed
Second stage assembled.JPG
Second stage assembled
first and second stage.JPG
first and second stages
clean pump assembled.JPG
Assembled pump ready to be attached

richnormand
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Re: Vacuum pump rebuild

Post by richnormand » Sun May 06, 2018 3:25 am

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 » Sun May 06, 2018 6:55 am

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
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

richnormand
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Re: Vacuum pump rebuild

Post by richnormand » Sun May 06, 2018 6:04 pm

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 » Mon May 07, 2018 2:05 am

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 » Mon May 07, 2018 7:07 pm

""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
notes007 (Medium).jpg

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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman » Mon May 07, 2018 9:29 pm

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.
DSCN0872.JPG
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.
Richard Feldman

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