Fusor Forums

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:
upper stage diffuser

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.

pump inlet

matching flange on the cold trap; notice the silver compound on both

stack after cleaning

cold trap after cleaning
reassembled and cleaned pump, upper flange not really cleaned yet.

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

Richard Hull

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.

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.

Images came through fine now.

Richard Hull

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

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

Richard Hull

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

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

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

The issue I have had with Indium is that it is single use. Has to be replace each time the components are dis-assembled. Also, steel expands a lot with temperature and Indium does not easily accommodate such expansions without being deformed in a permanent manner (when further compressed, it is going to have issues when the metal re-contracts) - that could be an issue for a diffusion pump that cycles. May not be an issue but do consider that.

Unless the issue is cryogenic mating surfaces or ultra-high vac (10^-7 and higher), I have no issues with low cost gaskets.

Isn't it also imminently remeltable though?

Yep, it is. Its very soft too, you can put dents into it with your fingernail.

Indium is one of the softest of all the elements. I makes lead look like stainless steel. Some of the nasty metals like those on the extreme left of the chart might be softer but are unusable structurally or for most all purposes in the real world.

You can stand over a molten vat of indium, 153 deg C, with an inverted funnel and hose leading to your nose and snort th' stuff as it has, effectively, no vapor pressure until it gets near is monstrously high boiling point 2000 deg C.....3000+ deg F


You can write very nice, long, conductive paths on paper or wood with a stick of indium metal. I have had my hands turn silver handling the stuff. According to the "Rare Metals Handbook" there is no recorded case of industrial Indium heavy metals poisoning. As with many metals, there are rare instances recorded of contact dermititus with long term repeated handling.

Aluminum has far more industrial contact dermititus instances reported.

Indium is a fun metal, one of my favorites, and I have about 5 kilogams on hand.

Richard Hull