Diff Pump Design

[Quantum]

I've spent considerable time over the Christmas period researching diff pump design, Steve Hanson's Bell Jar site has been useful, but so far, I've not yet come up with a design that satisfies all of my requirements.

I've found several designs, with drawings, ranging from one inch single stage pumps upwards.

I've decided I probably want a three stage design, and I've read somewhere that it's possible to arrange the oil 'feedback' so that lighter fractions are boiled off first, and are directed to the lower stages, leaving the heavier fractions to be directed to the top stage. This minimizes backstreaming.

None of the designs I've found satisfy these criteria, so unless anyone here can point me towards a suitable design it looks like I'll have to design one from scratch.

As usual, any assistance here will be appreciated.

[Carl Willis]

Ash,

Almost all modern commercial diffusion pumps are three-stage, fractionating designs.

Fusor-suitable diff pumps with aforementioned features routinely sell for under $100 on eBay.

I doubt there's any particular virtue to reinventing the modern diff pump, unless purely for personal edification on the subject of diffusion-pump engineering (in which case go for it, just don't expect to save money or get to fusion more quickly by fabricating one-off custom designs).

-Carl

[Chris Bradley]

Unfortunately for Ash, he is in the UK where I've not see a diff pump come up for several months. (There's been several turbos come up, though, in that price range - I know, I bought 'em all!! )

Ash, I hope you do try building one and not just talk about it. For a fusor, you won't need the ultra e-9 vacuums, but just enough to 'augment' a rotary pump and help clear out the contaminants before feeding in the D, so you might pull it off with a home-brew single stage. As Carl says, depends what you want to get out of it. It'd be good if you got on and built something, but probably easier and cheaper to get on with a fusor build and ship a diff pump in from the US if you're not actually that interested on diff pump tech.

[Tyler Christensen]

I ironically had my diffusion pump sent over from the UK, nice little NW50 air cooled pump brand new from Edwards Clearance Center. It was on ebay but it looks to be a pretty official source since all they sell is Edwards vacuum parts. You might try getting in touch with them to see if they could help you find one (nothing listed right now but who knows what they have in stock). Their ebay username is edwards_vacuum_clearance_centre

[Chris Bradley]

50% of all the vacuum kit in my lab is from them. Thoroughly recommended! The last diff pump from them I saw was, infact, the last one I've seen on ebay UK (maybe that was the one you bought!!).

[Quantum]

The only diff pumps I've seen for a reasonable price from the US recently were 11" ones. If I could find what I want, I'd buy it.

We've established that 2" diameter is sufficient. Three stage, fractionating, water cooling, and a cold trap are the rest of my criteria.

I'm sure if one did happen to come up on Ebay, We'd all be bidding for it.

[derekm]

I have a diffstak 63 in pieces at the moment. I could do some measurements and photographs for you

[Quantum]

That's exactly what I'm after, Derek.

That would help me enormously.

BTW, How is your Peltier cold trap design coming on?

I'm interested in what device you plan to use, and how you intend to incorporate it into your system.

I've asked this in the backstreaming thread, but I don't believe you've posted a reply yet.

Maybe you are still at the planning stage?

Thanks in advance for photos/dimensions of the diffstack 63.