Edwards Diffstak disassembly and cleaning?

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Rob MacLachlan
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Real name: Rob MacLachlan

Edwards Diffstak disassembly and cleaning?

Post by Rob MacLachlan » Thu Nov 30, 2017 5:36 pm

I picked up a Diffstak 63 on ebay. Looks nice on the outside, but seems it's pretty gunked up on the inside. Does anyone have a manual for Diffstak pumps or have experience with taking this apart? In conventional diffusion pump design it seems that usually the jet assembly will just fall out. I'm not seeing anything like that, but it looks a lot different inside due to the builtin cold cap/baffle arrangement.
dp_parts_scale.jpg
I took off these parts, the retainer bar that comes off just by turning it, the cap, and the spring underneath.
dp_innards_scale.jpg
Now I see this large aluminum part. It does not fall out, and does not seem to move at all, to rock or rotate. The only suggestive/odd thing is that there is a threaded hole in the top center which does not have any bolt in it. It occurs to me that I could use that to pull with if I could find the right bolt (probably metric). I also wonder if there is a missing part, though it couldn't be very big because the spring sits in that circular recess.

My top theory is that the jet assembly is glued in by a tar or carbon deposit. I have mineral spirits (petroleum distillate) in there, and have flushed it out, getting a lot of what look like carbon particles, enough to make a jarful look black, but not to significantly discolor small amounts. My feel is that I am not really dissolving anything, just flushing out loose carbon.

Has anyone run into something like this? Lacking any better info, if the mineral spirits isn't doing anything, I'm going to try heat next, combined with pulling on the jet assembly. I could also just try seeing if it works after flushing out all the crud that I can.

Rob

MatthewL
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Re: Edwards Diffstak disassembly and cleaning?

Post by MatthewL » Thu Nov 30, 2017 6:34 pm

Rob,

I have taken apart one these as well. The aluminum part is the top of the Christmas tree, and turning the whole pump upside down after removing the retaining bar should allow the whole assembly to fall out. You are most likely right in your assumption about the assembly being stuck by tar or carbon deposit. From what I can tell you don't seem to be missing any parts. The top threaded hole is there because a threaded rod is screwed into it from the other side to hold the rest of the jet assembly together.

This is the only information that I have been able to find on it http://www.idealvac.com/files/brochures ... _Pumps.pdf
Maybe Edwards would be willing to give you a more detailed manual.

-Matthew

Rob MacLachlan
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Re: Edwards Diffstak disassembly and cleaning?

Post by Rob MacLachlan » Thu Nov 30, 2017 8:08 pm

Thanks for the info! I'll press on. If moderate heat from the heater won't do it, I'll take off the heater and try a propane torch. Even if it's pure carbon it should be possible to burn it out without melting aluminum.

Do you know anything about the seals on the oil fill/drain plugs? Some mention of o-rings in the Edwards online info for current version of the pump, but what's in there now is pretty much a cone shape. Possibly it just distorted due to time, heat and pressure?

The cooling water inlet is at the top, and water outlet near the backing connection?

If this is the stock compression fitting on the water lines, do you have any idea what it is? A 6mm compression fitting, whatever that means in the UK. I'm guessing I have to either cut it off or use a rubber tube and hose clamps.

Rob

MatthewL
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Re: Edwards Diffstak disassembly and cleaning?

Post by MatthewL » Sun Dec 03, 2017 12:00 am

The seals for the drain and filler plugs are small, round Viton o-rings. New ones can be ordered from Edward's, but shipping to America can be sort of long and trying to make an account with Edward's can be difficult as well. I would recommend just ordering some Viton o-rings from a place like McMaster-Carr. I ended up ordering them from Edward's and the dimensions are 10mm OD and a 5mm ID.
For the water cooling inlet and outlet I just use hose clamps and rubber hose. My pump also has those compression fittings, but I haven't gotten around to getting a proper connection made. I wouldn't recommend cutting off part of the pipe incase your want to use the fittings later. I just unscrewed the nut and stretched the hose over the ferrules. For the cooling water inlet I have just used the top inlet, and the pump works fine.

-Matthew

Rob MacLachlan
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Re: Edwards Diffstak disassembly and cleaning?

Post by Rob MacLachlan » Sun Dec 03, 2017 10:50 pm

I made some progress. I was able to get a manual pdf just by asking Edwards customer service nicely, though my saying I was from CMU on the contact form may have helped. I've put it up on the net here:
http://humancond.org/_media/wiki/user/r ... manual.pdf

Here's a cutaway drawing from the manual:
diffstack63_cutaway.png
I was able to pull out the jet stack after heating it up using the heater. It turns out that the tapped hole in the top of the jet assembly is for a puller, although the tool is not described in the manual. The threads are M5. I've described my adventures thus far here:
http://humancond.org/wiki/user/ram/vacu ... diffstak63
See this page for pictures of my rusty-screwdriver actuated puller.

I tried, and it turns out that the water fittings on mine are 1/4 NPT. Interestingly the tubing itself is 1/4", not 6mm.

Yes, it seems the seals are supposed to be o-rings. If the o-ring looks like a cone, I guess that would be an example of the "heat set" referred to in the manual. Thanks for the replacement ring dimensions.

Rob

ian_krase
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Re: Edwards Diffstak disassembly and cleaning?

Post by ian_krase » Mon Dec 04, 2017 12:40 am

The OringStore sells irons
Orings in single quantities.

John Futter
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Re: Edwards Diffstak disassembly and cleaning?

Post by John Futter » Mon Dec 04, 2017 6:43 pm

Rob
Please try to post all your relevant info to this site and do not link other sites for content as when it inevetibly happens the external site stops for whatever reason this thread becomes worthless

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