Identifying Diff Pump Inlet Type

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John Beutz
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Identifying Diff Pump Inlet Type

Post by John Beutz »

I ordered a diffusion pump off eBay, unwisely assuming that the inlet was a 2.75" CF.
s-l1600 2.jpg
While the pump was shipping, the seller told me this when I asked about the flange:

"I haven't found a matching flange via googling. It is similar to a Conflat, but doesn't have the required knife-edge to seal against a copper gasket. And it's about halfway between 2 3/4" and 4 1/2" Conflats, so it is not a Conflat. The closest I have found is an ISO 63 F-style flange, but those have a narrower cutout where the seal centering ring fits as compared to this, and again this is between sizes so it isn't that. It's either proprietary, or something obsolete I can't find. It probably was an o-ring set into the gland on the pump, and the pump bolted to a flat surface with matching threaded holes, and whoever bought these new could easily machine their vacuum chamber to match this. Since it should seal against a flat plate with holes, it should be relatively easy to make something work, depending on your application."

Since the inner diameter of the diff pump inlet is approximately similar to the outer diameter of my KF50 chamber, I was thinking of maybe simply welding a 90 degree KF50 cross to the diff pump inlet. Unless, of course, somebody here can identify the flange type. Then I'll just buy an adapter, if I can find one for a reasonable price. Is there any reason why welding the KF directly to the diffusion pump inlet is a bad idea? I'm really not 'in the business' of spending a weekend or two slaving over machining my own custom SS flange, but it may be necessary if this pump's inlet was some custom made oddity. Thanks as always,

John
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Rich Feldman
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Re: Identifying Diff Pump Inlet Type

Post by Rich Feldman »

John, please don't do any welding that will interfere with pump cleaning & maintenance.

How about following the hint from your ebay seller? Permanently attach your chosen fitting to a flat plate with a round hole in the middle and a bolt pattern that matches the pump flange. If the plate warps from welding or brazing, make it sufficiently flat & smooth again. Seal the new adapter to pump with an O-ring, or a gasket cut from rubber sheet. This assumes that you are making a fusor & not some high-vacuum apparatus.

The adapter could be a place to drop in different-sized apertures to cheaply limit the pumping speed.
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Richard Hull
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Re: Identifying Diff Pump Inlet Type

Post by Richard Hull »

Surplus diff pumps are famous for oddball flanges related to some manufacturer's custom design and I would say 80% of all diff pumps have really odd, non-standard flanges.

It is incumbent upon the buyer to adapt it to something standard by manufacturing a custom adapter plate and stock flange suitable for his system. Diff pumps with conflat fittings are just never, ever encountered, Though I am sure you could order one new for $$$$.

The oddball flanges are due to the pump being part of a custom system designed to do a job that the manufacturer would like to keep in-house for repairs and use his specialty fittings. Many of these diff pumps offered with odd flanges are removed from salvaged gear where the vacuum system was just a small part of the whole.

If you buy a diff pump from a normal manufacturer, in the vacuum market, new, it will always have a standard flange. Odd flanges are just salvaged items from custom shops and builders of systems.

You are out on a very common and familiar limb.

Richard Hull
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Jerry Biehler
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler »

Yep, dont modify the pump, just make an adapter. A simple plate will do with he six bolt holes and then a hole in the center to fit a KF50 centering ring and use a bulkhead style clamp to attach your KF fitting to that: http://www.mdcvacuum.com/DisplayProduct ... 1.h&g=m1a1

Just make sure you dont drill all the way though when you drill and tap for the bulkhead screws. You can make the adapter out of a lot of things, aluminum, brass, stainless and even some plastics like PEEK and Vespel.
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Rich Feldman
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Re: Identifying Diff Pump Inlet Type

Post by Rich Feldman »

Better & better, eh? I'd forgotten about bulkhead clamps, which is sad 'cause I've used them to put KF25 flange on a flat plate.
viewtopic.php?f=10&t=3977&p=25528#p25528

3/8" plate is thick enough to make the closed-end threaded holes. 1/4" is thick enough for the stiffness you need, even in aluminum. As Jerry said, you don't need stainless steel for this. Needless cost & machining trouble.

You _could_ simply drill & tap all the way through, then seal off the holes on vacuum side. Or run longer 10-32 screws through with heads on the vacuum side & use nuts on the bulkhead clamp side. Details are left as an exercise for John.
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Silviu Tamasdan
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Re: Identifying Diff Pump Inlet Type

Post by Silviu Tamasdan »

Thank you for this thread. I guess it explains this:

Image

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My latest find, a CVC PMCS-2C with attached cold trap BC-20A. Couldn't find any information on the trap, but I did find the manual for the pump - first somewhere else, then on this board too. The pump and the trap seem in good condition, the heater tests at 48 ohms which is the right ballpark for the stated 300W/120V. But that inlet is nonstandard, 4" OD and 2.25" ID with that inner ridge (it's actually a groove on the pump per the manual) where a proprietary "con-o-ring" is supposed to go. I have in the manual the part number for the ring from the now defunct CVC, fat good that will do. But I suspect there is one of the infamous con-o-rings between the pump and the cold trap, I'll find out when I disassemble it for cleaning (won't have time until next week). Perhaps I'll be able to find or fabricate a suitable replacement. The pump came with some plumbing attached, including this:

Image

Looks a little deformed but hopefully still works. If not, oh well.

I'm thinking that probably the best way to go about it is to standardize my high vacuum end connections on KF-50. That's because my other pump (Edwards EO 50/60) uses that also, and it's size appropriate for this pump too. Probably a flat plate bolted to the intake, with either a half-nipple KF-50 welded. or a full nipple attached with bulkhead clamps. This way I could change pumps easily if I need to. And probably convert the forepump connection to KF-10 as the Edwards pump has for more flexibility.
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ian_krase
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Re: Identifying Diff Pump Inlet Type

Post by ian_krase »

Con-o-ring? That sounds like the "Econo-rings" sold by Duniway and others.
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler »

Looks like you can get a o-ring for that here: http://www.idealvac.com/svpproduct.asp?pid=660892230
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Re: Identifying Diff Pump Inlet Type

Post by John Futter »

Silviu
please get rid of that teflon tape that you have attempted to seal off to your vacuum gauge
Use locktite 290 or preferabley soft solder to seal.
Teflon tape is to seal gas and water pipes not vacuum fittings
Silviu Tamasdan
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Re: Identifying Diff Pump Inlet Type

Post by Silviu Tamasdan »

John Futter wrote:Silviu
please get rid of that teflon tape that you have attempted to seal off to your vacuum gauge
Use locktite 290 or preferabley soft solder to seal.
Teflon tape is to seal gas and water pipes not vacuum fittings
Of course, it's on the to-do list. I'm not the one who used the tape, it came that way. Soldered joints is what I plan to use. I will remove all of the old added hardware especially since some of the pipes are bent shut and make my own custom fittings.
Jerry Biehler wrote:Looks like you can get a o-ring for that here: http://www.idealvac.com/svpproduct.asp?pid=660892230
Good find, thanks. I will have to disassemble the pump from the cold trap and measure the oring that I suppose I will find inside that joint to make sure that the one in the link has the correct dimensions.
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler »

Honestly, on the roughing side of things teflon tape is fine. Don't solder stuff, especially using regular solder, you need to silver braze.
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Re: Identifying Diff Pump Inlet Type

Post by Silviu Tamasdan »

Well I don't intend to solder directly the diff pump to the forepump if that's what you mean. :) I want to solder (or braze, but using solder would be easier) a KF-10 adapter to the diff pump outlet so I can use KF-10 hardware between it and forepump.
I've read in several places that using lead-tin solder is fine, especially on the low-vacuum side.
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler »

Chances are the fitting is going to be stainless and that wont solder with standard solder. You either need silver solder or sil-phos.
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Re: Identifying Diff Pump Inlet Type

Post by ian_krase »

I prefer Loctite 290 because I can take it apart.
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Re: Identifying Diff Pump Inlet Type

Post by John Futter »

Jerry
Hard Silver solder is not good for stainless where as ordinary solder works just fine
You have to have the right flux (killed spirits of salts with a 20 drops of Phosphoric acid added {and two drops of HF acidif you can get it})and not over heat the stainless, vacuum tight joints to 10 to the minus nine millibar no problem

Teflon tape is shit in the hands of the amateur I see this post has already slavered some other compond over the tape presumeably to try to fix a leak.
Teflon creeps so a leak that is sealed today will be a horrendous leak tomorrow.
The correct way to use it is to minimize the amount so it is used as a lubricant to allow the joint to be made by compression/ interference --not some huge amount of extremely slippery tape packing that moves to reduce pressure in the joint and allow a leak

We make Ln2 coolers for our systems and all use soft solder (60:40 tin lead) (you could use other soft solders especially those with a few percent silver) to join copper to stainless these joints go room temp to -197 Degrees C several times day
and do not leak according to our Helium leak detector, the final proof of ultimate vacuum of 2 by ten to the minus 8 millibar using a pfeiffer turbo.
If you use silver solder (hard solder silfos etc) it will crack sooner than later. Our experience a couple of weeks before a leak opens up, soft soldered joints now going ten or more years with no leaks.

Usually soft soldered threaded joints can be unwound by using a little heat (nowhere the melting point) and the bonus is you can redo them with out heating and they reseal perfectly.

I've only been doing this for forty years and no failures yet
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Re: Identifying Diff Pump Inlet Type

Post by ian_krase »

Wait, silver brazing lasts *weeks*? How big are these leaks?

Because that would suggest that my entire system would be leaking like a sieve which it isnt.
Silviu Tamasdan
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Re: Identifying Diff Pump Inlet Type

Post by Silviu Tamasdan »

It may definitely depend on what conditions the joint is exposed to. If it goes through several cooling/warming cycles a day to LN2 temperatures, I can see how a stiffer solder could develop cracks where a softer one wouldn't. Whereas if it's more or less at RT all the time that wouldn't happen.

Thanks for the information everyone, it's pretty much in line with what I had been reading. I have experience with soft soldering (mostly for electrical work) so that would be an easier approach for me (though I've never done copper to SS before; I knew about that flux formula though). I did order a small amount of silver braze and flux and will be experimenting with it - I don't have oxy-acetylene equipment though, I hope a MAPP torch will work. The pump outlet is a 3/4" pipe connected to a several pounds mass of metal, so I may run into issues with heat transfer. If a regular torch doesn't work, I have parts to assemble an H2/O2 generator (fortunately those are relatively cheap and plentiful due to the "HHO" craze) and may use that to fuel an oxy-hydrogen torch.

John, about that flux. The only kind of HF I seem to find is 10% gel for dental porcelain etching, like this one: http://www.ebay.com/itm/PORCELAIN-ETCH- ... SwZ1BXegWW Do you think that would work in this application?
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John Futter
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Re: Identifying Diff Pump Inlet Type

Post by John Futter »

Silviu
I do not like flame type soldering very much
If your MAP torch is heating a soldering bit OK
I use an electric 150 watt iron.
First I clean the area with a SS wire brush then using a cotton bud or similar
I coat the area to be soldered with flux
with a reasonable amount of solder on the bit I hit the fluxed surface and rub the bit back and forth
all going well the area should be perfectly tinned.
If you overheat the area you have to regrind all affected areas and start again

not sure about your gel
but alot of hardware shops sell glass frosting fluid (30% HF)

Ian
Yes a Fusor with hard soldered joints will fail due to the heating and cooling due to fusor runs
has alot to do with the differing contraction /expansion rates of the solder the SS and any other metal / alloy introduced
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler »

HF? Be very careful with that stuff, goes right through your skin and attacks your bones. Then you get to have a calcium gluconate drip so it goes after that instead of your bones.
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