Diff pumps cleanout

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Silviu Tamasdan
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Diff pumps cleanout

Post by Silviu Tamasdan » Thu Sep 07, 2017 6:53 pm

I set today to do a preliminary cleaning of the 2 diffusion pumps I have: an Edwards Vapor Pump EO 50/60, and a CVC PMCS-2C.

With the Edwards I hit a snag. The pump I have is actually modified, and I hadn't even realized it until today. Instead of the standard KF-50 inlet flange it has a custom 40mm flange. It almost looks like a KF-40 but doesn't have the inner channel for the ring. The bore of the whole flange throughout is 41mm, so I think it will work with standard KF-40 hardware. But because it's narrower than the KF-50 I wasn't able to remove the whole jet assembly; the upper stage and retaining clip came out easily, but the lower stage is just a bit too wide to fit through the 41mm opening. I tried several ways and it just won't come out. Bummer. Now, according to the manual http://shop.edwardsvacuum.com/Viewers/D ... vkM4b6cH5Q there is an ejector tube under the second stage and I'm not sure that is fixed or mobile; there are probably some guides at the bottom of the pump for the lower stage to sit on, as it fits back in 3 different positions (two of them are 180 degrees from each other, and the third is about 60 degrees from one of the other two). I can't really see inside the pump as the lower stage diffuser blocks the view so I don't know what is the correct position to reassemble it. :(

Pictures:
20170907_092407.jpg
Edwards upper stage diffuser
upper stage diffuser

20170907_092412.jpg
Edwards inlet
view inside with the lower stage stuck in place (before cleaning)

The other pump is a CVC PMCS-2C which came with a cold trap attached; I posted about it in the other thread viewtopic.php?f=10&t=11117
I had some time today and disassembled this one too for cleaning. I was hoping to find what the "con-o-ring" mentioned in the CVC manual is, but...no. After I loosened and removed the 6 bolts holding the 2 together, I couldn't pry them apart. I had to use a screwdriver tip inserted between the 2 to twist the joint open. After I was able to separate them, I found out why. They had been glued together!
At first I thought there had been an aluminum O-ring placed between the 2 flanges as there were traces of something silver-colored in a ring on the flanges. It was really well stuck and after rubbing it with acetone and alcohol it become rubbery and I was able to take it off with a lot of work (I didn't want to scrape with anything harder than my fingernail). It looks like some sort of silvery glue. It's not epoxy. I dunno what it is, any ideas?
Anyway, I managed to get most of it off from the vacuum trap flanges; I ran out of time and couldn't get the pump flange cleaned. The pump was pretty clean inside, just a tad of carbon residue on the inside of the stack that came off very easily.

20170907_130813.jpg
CVC pump inlet
pump inlet

20170907_130819.jpg
cold trap inlet
matching flange on the cold trap; notice the silver compound on both

20170907_132525.jpg
stack after cleaning
stack after cleaning

20170907_133954.jpg
20170907_134010.jpg
cold trap after cleaning
20170907_134237.jpg
CVC partially cleaned
reassembled and cleaned pump, upper flange not really cleaned yet.
Last edited by Silviu Tamasdan on Fri Sep 08, 2017 10:14 am, edited 6 times in total.
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Richard Hull
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Re: Diff pumps cleanout

Post by Richard Hull » Thu Sep 07, 2017 7:34 pm

Of course, no images came through in the above post.

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Re: Diff pumps cleanout

Post by Jerry Biehler » Thu Sep 07, 2017 8:59 pm

Kinds looks like some silver silicone. You can just use a razor blade to clean it up. It will be fine.

My guess is they couldn't find a replacement seal and went with sealant to put it back together.

Silviu Tamasdan
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Re: Diff pumps cleanout

Post by Silviu Tamasdan » Thu Sep 07, 2017 9:04 pm

I've edited the post, can you see the images now?

About the seal, now that I think about it the texture is about right for silicone, and the fact that with solvents it would swell a bit but not dissolve. Of course that doesn't fix my own problem of finding an appropriate seal.
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Richard Hull
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Re: Diff pumps cleanout

Post by Richard Hull » Fri Sep 08, 2017 7:10 am

Images came through fine now.

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.

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Re: Diff pumps cleanout

Post by Jerry Biehler » Wed Sep 13, 2017 1:51 am

You could do a wire seal: https://www.pfeiffer-vacuum.com/en/know ... tal-seals/ I would probably use indium.

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Richard Hull
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Re: Diff pumps cleanout

Post by Richard Hull » Wed Sep 13, 2017 4:23 am

I used indium seals exclusively until I went conflat in 2004. They worked out fine for me.

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.

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Dennis P Brown
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Re: Diff pumps cleanout

Post by Dennis P Brown » Wed Sep 13, 2017 9:43 am

You could easily cut your own circular gasket (depending on the quality of vacuum you need - for a fusor that would work well.)

Silviu Tamasdan
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Re: Diff pumps cleanout

Post by Silviu Tamasdan » Wed Sep 13, 2017 12:46 pm

Indium seals are a great idea! Wish I had thought of it earlier.
I actually have indium, but... it's not wire. I have about 200g of indium beads. It's very malleable and ductile, I wonder if I could carefully hammer it into shape... or melt it and cast in the shape I need. Not sure what I would make the mold out of. Silicone maybe? I'll have to investigate.
(edit) seems like there are some answers here https://chemistry.stackexchange.com/que ... ing-indium
I wonder if this would work:
1. make a mold out of silicone in the shape of an O-ring
2. break the indium beads into small bits
3. place the indium uniformly in the mold
4. use a heat gun to melt the indium in place, and let it solidify in the mold
Hopefully something like this would work for making the mold out of: Permatex 81160 High-Temp Red RTV Silicone Gasket https://www.amazon.com/dp/B0002UEN1A/re ... 8IUJY?th=1
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Re: Diff pumps cleanout

Post by Jerry Biehler » Wed Sep 13, 2017 6:03 pm

Indium will melt on a hot plate, I used it to bond targets to backing plates for sputtering and used a hot plate to solder them.

That silicone wont work for molds it will take forever to cure. If I were to try that I would use a platinum catalyst silicone or just good old plaster. Personally I would just buy some wire, you can get more than you will ever need for seals for $20 on ebay: http://www.ebay.com/itm/Pure-Indium-Wir ... 0507.m3226

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