Diff pump

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Jgn1
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Diff pump

Post by Jgn1 » Tue May 22, 2012 9:05 am


Hello there!

Is it mandatory to get an air-cooled Diff pump? Isn't a good idea to use water cooled ones? Which are the equivalent to the Welch, Edwards, Precision for the diff pumps?

Juan

Jerry Biehler
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Re: Diff pump

Post by Jerry Biehler » Tue May 22, 2012 10:05 am

Air cooled is more convenient. Water cooled works better for things that are buried in a cabinet with no air or temperature and vibration equipment around them. Like electron microscopes. If you have a source of water or a recirculating cooler with enough pressure (~45psi) go for it.

All the major manufacturers make DP's. Edwards, Varian, etc.

Though with the recent dumping of cheap turbo pumps on ebay and home brew controllers here a few are skipping DPs.

Jgn1
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Re: Diff pump

Post by Jgn1 » Tue May 22, 2012 8:59 pm

Thanks for the reply Jerry!

Well I have these two options:

http://www.ebay.co.uk/itm/EDWARDS-EXT70 ... 4292wt_758

This is a lot of money. Is this a very good price? Is it worth to make an ultra effort to get the money? Besides the Fusor I would like to perform many other experiments.

Does a Turbomolecular pump works? For example:

http://www.ebay.co.uk/itm/Balzers-Pfeif ... 500wt_1006

Same questions as 1.

Jeff Robertson
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Re: Diff pump

Post by Jeff Robertson » Tue May 22, 2012 11:45 pm

Hey Juan,

I would definitely recommend a diffusion pump over a turbo pump. They both serve the same purpose, but a diffusion pump is many times cheaper and (in my opinion) easier to maintain. Occasionally you can get a diff pump on ebay for under $100, while it's almost guaranteed to find a couple of them $100-200.

I use a water cooled diffusion pump in my fusor. It is a little more effort to rig a water cooling system, as opposed to an air one, but that shouldn't scare you away from it if you find a good deal or something. My pump had the spiral tubing around the diffusion pump (for the water cooling system) already in place, so I just bought some plastic tubing from Home Depot and an aquarium water pump from Petco (hah!). I just have the pump and the ends of the tubing in a large bucket of water, and it runs beautifully.

But yeah, I personally never saw the point in a turbopump unless you already have one lying around.

Jeff

Jgn1
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Re: Diff pump

Post by Jgn1 » Wed May 23, 2012 12:07 am

Thanks for reply Jeff!

hmm, I see. So what's the point of a Turbopump then?

I found this diff pump on Ebay Germany. You think this would work ok?

http://www.ebay.de/itm/Quecksilber-Diff ... _527wt_991

Could you upload or send me a pic of your diff pump set up?

About the Turbopump. 900 pounds still very expensive for that, right?

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Rich Feldman
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Re: Diff pump

Post by Rich Feldman » Wed May 23, 2012 12:27 am

Wow, that glass mercury-vapor diffusion pump is a classic.
If I lived in Germany, would bid on it, just as a collectible gadget.
I'm not afraid of boiling Hg, nor am I cavalier about its hazards.

Perhaps it will work with modern diffusion-pump fluid, instead of mercury.
Our vacuum experts may know whether the heater or nozzles need to be changed.

Rich

p.s. Haste will cost you money.
Not having a deadline, I eventually acquired an air-coiled oil diff pump with fan & throttle valve for $75. And a Tribodyn self-contained turbo-drag system (incl drive electronics & backing pumps) $300. Looks just like http://www.pchemlabs.com/product.asp?pid=1079
All models are wrong; some models are useful. -- George Box

Jgn1
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Re: Diff pump

Post by Jgn1 » Wed May 23, 2012 12:37 am

These are the spec. given by the seller:

"a 3 stage mercury diffusion pump that reaches a high vacuum of 1.3E-6 mbar at a pump rate of 360l/min. It has tobe supplied with 220V/50Hz and 500W. A backing pump is needed, that is able to pump down to 20mbar via the NS14 ground glass joint. The High vacuum side is connected by a NS29 joint."

"The pump is used but in good condition."

Juan

Jerry Biehler
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Re: Diff pump

Post by Jerry Biehler » Wed May 23, 2012 9:06 am

Turbo has a lot of advantages. One is pump down speed. You turn it on and spend up within a minute or two and is going. A DP has to warm up. Even the small one on my friends SEM takes about 20 minutes to warm up, same for the 6" in my deposition system.

Turbo pump is short for turbomolecular pump. There is also a Turbo-drag pump which is a subcategory. They allow for higher fore line pressures so you can run them from diaphragm pumps.

This may not seem like much of a deal, but if you are opening the chamber a lot it can save you the hassle of installing isolation valving around the DP so you can work on it and then pump back down.

One other thing about newer turbos is you can slow them down to throttle them. This will save you on D2.

Also DP's back stream without a cold trap. This means some of the oil vapor works it way back through the system.

But DP's a pretty indestructible. If you let a turbo up to pressure while it is still running it is probably going to be toast.

That being said, I will keep using turbos in the future. They are very reasonably price on ebay used.

That first pump with the complete setup is really nice. Complete dry system. No oils. Actually a pretty good price, I would say. Pretty much the perfect size for a fusor. Wont have to throttle it down as much.

Tyler Christensen
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Re: Diff pump

Post by Tyler Christensen » Wed May 23, 2012 11:15 am

A lot of turbo's take forever to turn off, making DP's just as good from a speed perspective. My little NW50 air cooled DP turns off about twice as fast as the little 4.5" turbos I use at work (which clearly don't have magnetic braking). With very careful gas bleeding that can be accelerated to about 1.5x slower for the turbo, but it still takes about 20 minutes. DP cooling can also be accelerated by putting a cold-liquid bath on the bottom.

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Dennis P Brown
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Re: Diff pump

Post by Dennis P Brown » Wed May 23, 2012 11:32 am

I have both systems - a turbo and diff. pump (oil) - on my accelerator. Both work very well (I do not run them simultaneously.) The diffusion pump gets down to the same vacuum level and is (once it gets to temp) very fast (I do not have a trap.) That said, I always use the turbo. Besides fast operation, no water is running and no cool down issue after shut down (that is important for Diff. Pumps! Otherwise you can crack the oil if any large amount of O2 gets to the hot oil.) By the way, my diff. pump has a special water connector for the hot oil (to rapidly cool) but I never hooked it up - the pump is a backup only. That said, look for one that does (mine is a Edwards) that would be a great time saver!

My turbo has a special inlet for rapid shut down. This works great because as one person pointed out, they take forever to shut down (don't free vent to the air!) My shut down vent is hooked up to a dry air filter and I use this to purge/back fill my system. This allows my accelerator to get under 5*10 -5 torr in under ten minutes after venting to the atmosphere.

I would say that cost wise, a diff. pump is far cheaper and will do the job - both units for a fusor, by the way, will need a main throttling valve/Gate valve on their intake.

Now and then, a turbo is overlooked on e-bay and a good deal can be had. Since that is rare (you need a controller, don't forget - check out Alexi's homemade controller for a very commonly available turbo pump) deals on good diffusion pumps occur all the time. That said, I'd NEVER own a Hg based diff. pump. Those vapors are deadly and without a cold trap, Hg will back stream and contaminate all your lines and the fusor. Then, every time you open the fusor, Hg vapors will leak. Remember, that Hg emits a lot of vapor at room temperature and that 70% of all Hg vapor you breath, is absorbed into the blood stream. Just saying.

Hg is not cheap to buy and must be disposed of legally and that isn't cheap - diff. pump oil is readily available on e-bay and the price is very reasonable (diff. pumps should never be sold with oil in them and if so, you need to get rid of that oil.)

By the way, my diff. pump is water cooled but I have water/drain system in my den (I installed. I really liked how the one person solved that issue using an aquarium water pump - really impressive!)

Your call on what suits your needs and wallet.

By the way, I have bought two outstanding two stage high performance vacuum roughing pumps on e-bay for under $100 for one and under $50 for the other (both these prices included shipping!) Deals on these units occur all the time (the other unit is in storage in the event that my primary fails. I like to backup all major systems.) Don't get me started on the amazing deals the Chinese are giving 24/7 on SS fittings/seals and connectors ... . Always watch e-bay and learn what key words work - the deals can be amazing!


That all said, waiting can be an issue and even then, someone else my out bid you or drive the price up. As Jerry Biehler said, that first unit is a really nice unit for the price. IF I had the money (I don't) I'd really consider that system. A top grade vacuum system (a dry fore pump means no oil trap for the main is needed) that gets down near/to 10-7 torr (and that looks to have a high volume capability) like that can be used for so many applications besides fusors - an deuteron accelerator, or vapor deposition system to name two (the roughing pump could handle any sputtering application.) Again, your call.

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