Author Topic: Homemade Diffusion Pump  (Read 19647 times)

Geoffroy B

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Homemade Diffusion Pump
« on: December 22, 2008, 07:56:41 PM »
In much of the amateur litterature, I have read about the possibility of building diffusion pumps from standard fittings, but there is never much details. I wanted to blow my diffusion pump in lime glass, but then feared thermal stresses, if I ever tried forced cooling. I have then decided to go with copper fittings. Now what I want to know is if there are critical values for the pump to work. I'm not talking about efficiency here, just the essential. Also, if someone know which parameters affect the ''rated'' backing pressure and the pumping speed. Thank you for your help.
Regards,
Geoffroy B.

P.S.: Sorry for any spelling mistakes, english is my second language.

RLM56

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Re: Homemade Diffusion Pump
« Reply #1 on: December 23, 2008, 04:55:03 PM »
Hi,

I'm a beginner too but I have been reading the literature and buying old books on vacuum for over 2 years now.  Right off the top of my head I remember that you can't use copper for the diffusion pump body because copper will catalyze hot oil.  You need to plate the copper with nickel.  The pump body could also be made from stainless steel or regular steel.  As far as parameters of the actual shape, size and fit of the pump body and components you would be best off to copy an existing design.  Although from what I have read it would seem that you could make a pump of this type by following a few simple rules about the angle of the chimney cones and the clearance between the walls etc.  The type of oil you choose will determine how well your home made pump works too.  The performance you might realize from a home made pump is anybody's guess.  Possibly the best solution would be to buy one of the many surplus diffusion pumps that show up regularly on EBay.  You could buy more pump for under $100 that you might ever build in a month of Sundays.  Not that I'm against building anything but some things are a much better deal bought used/surplus than made at home.  I have found that in many cases you spend more on materials and tools than a used item would cost.  Unless you are doing it for the sole purpose of seeing if you can build a functioning diffusion pump by hand.......then by all means go for it!!

Roy

Steve Hansen

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Re: Homemade Diffusion Pump
« Reply #2 on: December 24, 2008, 05:30:09 PM »
Over the years I've heard from a goodly number of people who expressed a desire to build a diffusion pump. I even gave a fellow a 4" commercial pump as he wanted to copy it. So far I'm not aware of anyone who has done this. It's certainly not from the complexity of the task. I think that it is simply because it's fairly easy to buy an old pump off of eBay or similar.

If anyone really does want to build a pump, there are some old books that have dimensioned drawings and Frank Lee did a design for a 1" two stage pump that's in the First Five Years compilation. Somewhere in my stack of stuff are some of the commercial drawings and if someone is really interested I could make copies.

Geoffroy B

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Re: Homemade Diffusion Pump
« Reply #3 on: December 24, 2008, 11:47:49 PM »
Good advice for the copper, but I've read the deterioration of the oil is not too fast, plus I'm really not into welding. Do you know of any good solder wire for steel brazing?

Diffusion pumps are not that costly on eBay, but it would be rather difficult to get a pump under a hundred dollar for me (that's counting shipping to Canada), and for my project, a commercial diffusion pump is a bit overkill and takes too much place. What I need is a small booster pump of low pumping speed (really small chamber)  just to help my HVAC pump to reach 1 microns in short time (I will never go under 0.1 microns). These pumps are not showing often on eBay, and I doubt they even exist on large scale production, so I wondered if I could make a simple, but functioning diffusion pump (standard fittings are really cheap!). Also, a micromaze setup is not what I'm searching for because they're a bit costly with the added cost of sequential valves, etc. If you have any other cheap ideas to accomplish this goal, they're welcome! If I have no other options, I will try for a homemade diffusion pump and will post my results here.

Thank you for your help,
G.
Regards,
Geoffroy B.

P.S.: Sorry for any spelling mistakes, english is my second language.

Steve Hansen

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Re: Homemade Diffusion Pump
« Reply #4 on: December 25, 2008, 09:46:09 AM »
The copper thing is not an issue with synthetic oils (someone correct me if I'm wrong). However, it's a lot easier to machine aluminum.

I'll dig out some dimensioned drawings. I've got them in a box somewhere.


Geoffroy B

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Re: Homemade Diffusion Pump
« Reply #6 on: December 26, 2008, 03:06:39 PM »
Yeah, well, with the shipping it's more like $ 50, but still REALLY reasonnable. I saw the listing about one day ago, but the ''cryopump'' in the title made me fear it needed LN2, also, it doesn't look like any other pump I've seen. I concluded it was a kind of trap wrongly listed. But then a little googling seems to indicate it is a pump. For such a low price I'm almost ready to play my luck...
Regards,
Geoffroy B.

P.S.: Sorry for any spelling mistakes, english is my second language.

Geoffroy B

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Re: Homemade Diffusion Pump
« Reply #7 on: December 27, 2008, 12:15:30 AM »
Thinking about it, I am still curious to know if a simple design with standard fittings would, at least, ''work''. A single stage upjet or downjet pump like in the picture attached is really simple to assemble :
You could use standard 1/2" copper tubing for the chimney, 3/4" fitting for the condenser with intake and output, and 1/2" to 1" adapter, capped, for the boiler. The only metal work to be done would be soldering and drilling holes to solder the (1/4" flexible?) oil return. Now, I ask you, are the dimensions in a diffusion pump critical to assure functionality, or rather are they to enhance performances? Do this simple pump has a chance to work? I'm eager to try!

Thanks for the help!
« Last Edit: December 27, 2008, 12:24:52 AM by Geoffroy B »
Regards,
Geoffroy B.

P.S.: Sorry for any spelling mistakes, english is my second language.

Gerten Gertenbach

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Re: Homemade Diffusion Pump
« Reply #8 on: December 28, 2008, 09:28:52 AM »
See http://www.cientificosaficionados.com/tbo/difusion/difusora1.htm for detail of home made diffusion pump.
It's in Spanish, you can use Google or similar translating service to convert to English.


Geoffroy B

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Re: Homemade Diffusion Pump
« Reply #9 on: December 29, 2008, 05:13:52 PM »
Thank you for the link!
Regards,
Geoffroy B.

P.S.: Sorry for any spelling mistakes, english is my second language.

Steve Hansen

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Re: Homemade Diffusion Pump
« Reply #10 on: December 31, 2008, 11:20:49 PM »
Nice piece of work in that pump.

I found one dimensioned drawing for a "homemade" pump in a Los Alamos document from 1952. The pump is a 4" 2-stage unit with ejector with a speed of 200 liters per second. The pump was listed as compatible with silicone, Octoil-S or any other "conventional" pumping oil. Here is the link to the drawing: http://www.belljar.net/forum/dp001.pdf

This pump would represent a fairly complex project but it is fully dimensioned.

I have some other dimensioned drawings and will post them as I find them as I unpack

Steve Hansen

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Re: Homemade Diffusion Pump
« Reply #11 on: January 01, 2009, 12:40:33 PM »
I have compiled some notes and letters from Frank Lee concerning his thoughts on small homemade diffusion pumps. These are based on the Edwards EO1, a nice little 1 inch 2-stage pump. This may be found in the Frank Lee section on my articles page http://www.belljar.net/articles.htm. Scroll to the very bottom of the page. The file is in Acrobat format and is about 2.3M in size.

Gerten Gertenbach

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Re: Homemade Diffusion Pump
« Reply #12 on: January 01, 2009, 08:49:01 PM »
Thanks for sharing this. I'm one of those who once toyed with the idea of building a diffusion pump - allow me to share what I've learned in this quest:

The book "Creative glasblowing"(1968) by Hammerfahr and Stong have details how to build a two-stage mercury diffusion pump. You need to be skilled in working with boro-silicate glass (oxygen flame) to build this. I discussed this design with my local glassblower who told me his teacher passed away b4 he completed his apprenticeship, but the old master did tell him that the nozzles dimensions are very critical for the proper functioning of the pump. The book is out of print, I found a used copy via Amazon. It's a an excellent introduction to glass blowing, both scientific and artistic (my glasblower will not agree with this statement, but he's from the modern European school, the book describes the vintage American method using cross-fires)

I get the impression that with the exception of some Neon shops these designs are no longer used in industry. The only company that I could find that sell glass pumps are SVP http://www.svpneon.com/diffusion_pumps.html. Of interest is the controversy surrounding the usefulness of these single-stage pumps as mentioned by Coyne on p.368 of "The laboratory companion" (1997). Blazek&Blazek in "Neon - the next generation"(2003) mention that they have found very few working diffusion pumps in the US Neon industry...

Soft glass do not need an oxygen flame, but I doubt if even a well anealed piece of soft glass will be able to handle thermal stresses (as mentioned by Geoffrey). And finding soft glass with the right dimensions might no be that easy.

In the "Proceedings of the A.S.G.S. 1995 Symposium" Wheeler describes how to  build a 4" Glass Oil Diffusion Pump. Wheeler copied the dimensions of a commercial metal pump and achieved better performance than the original (375 l/s). I've attached some pictures out of the article, the dimensions look very similar to the Los Alamos design posted earlier by Steve. Once again you need to be well skilled in working with boro-silicate glass (at least a journeyman). Limited extra info at http://www.public.asu.edu/~aomdw/GLASS/DIFFUSION_PUMP.html

The manuals of metal diffusion pumps often contain detail of the internals, free downloads of manuals are available on both the Edwards and Varian websites. I've attached a picture I found in a Varian AX-65 pump manual. Looking at the drawings it should be easy to scale and copy using a small lathe (using Aluminium?). If you change the design finding the right heat input might need some experimentation.

As DIY'er the question I ended up with was if it would not be better and easier to build a Zeolite trap and not a diffusion pump? Published results suggest that you can equal the performance of diffusion pump with a Micromaze zeolite trap. I guess this refer to ultimate vacuum and that the pumping speed of trap will much slower? And unless I'm missing something the Micromaze is a commmercial simplification of what Kendall and David described in the article "High vacuum for teaching and research" in Am J.Phys 36(3),234, March 1968 (see tBJ summary http://www.belljar.net/82trap.pdf). It's a relatively simple device with a heater to bake it out, the 13X zeolite is not that difficult to source. Not freely available is what's called 'Columbine formula 6' to bind the zeolite to the metal surface, but somewhere I read that you might be able to use water glass....

Jan ;D

PS. Another example of (unfinished) homemade diffusion pump can be found at http://www.fusor.net/board/download_thread.php?site=fusor&bn=fusor_vacuum&thread=1172191668

Steve Hansen

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Re: Homemade Diffusion Pump
« Reply #13 on: January 01, 2009, 10:35:14 PM »
Jan,

I'll just pick up on a couple of items you mentioned. On the glass neon DPs, in a discussion back along with Mars Hablanian (I believe he actually did the tests), the specific pump was the Hickman upjet pump. As I recollect, he found that there's no real pumping action but the pump does act as a "stop" for backstreaming vapors from the mechanical pump. Therefore it's more of a trap than a pump.

And, speaking of traps, I really do like the micromaze but it has to be used with a small and pretty clean system to be effective. I calculated the effective pumping speed of my trap to be slightly less than 1 liter/second. It doesn't boost the speed of the backing pump but it does keep backstreamed component under good control.

Geoffroy B

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Re: Homemade Diffusion Pump
« Reply #14 on: January 03, 2009, 03:28:37 PM »
Thank you all for your answers!
I will keep you informed of my little experiment on a homebuild hickman type pump/trap in copper fittings. I know these kind of pumps will not permit deep vacuum work, but a small boost to the base pressure of an amateur vacuum system is the goal. And considering the cost of my project (about $40 with more oil than you could ever need for it), I think it is still interesting.
Regards,
Geoffroy B.

P.S.: Sorry for any spelling mistakes, english is my second language.