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Author: Subject: High vacuum CHEAP and dirty!
Hermes_Trismegistus
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biggrin.gif posted on 28-11-2003 at 22:40
High vacuum CHEAP and dirty!


Y'Know

If I was really interested in pulling a decent vacuum over a longish period of time I would hook a Diffusion Pump to a pressure rated tank (like for an air compressor or two mounted in series or something)

I know for a fact that if you wanted to, you could cobble one together out of metal on a fairly humungous scale that would draw a vacuum on the level of interstellar space

or just plain inner solar system space if you only used a single-stage pump.

I think the only time consuming part to fabricate might be the Helix. So....I would find some small stainless grain/earth auger to use and base the rest of my apparatus around it..

Even if you aren't handy with metalworking tools (and this would need to be VERY tight work) a man could find a youngish machinist who definitely wouldn't ask many questions and work cheap.

The best place to get a good machinist is to look for a younger guy/gal with a solo shop stuffed in some dark corner....by the time a shop has enought customers to support multiple employees they charge far too much to be valuable.

shop around...sometimes they get a run of work and start jacking prices up to cope, or start to starve and will work for the change under the drivers seat of your car!

Just remember to bring a detailed picture of the conventional apparatus and ask about surplus stuff they might be able to use.

An hour of explaining will save tonnes of heartache and sticker shock.

Machinists know very little about scientific equipment so you would have to take time to explain the basic principle to him...after that he can usually take the ball and run with it.

HINT* if your planning on pulling ultra-high vacuum, make sure they cut open the pressure vessel and install internal baffles for strength.

and you might as well get him to install a good vacuum manifold/ cold trap/ dehydrating intake filter right off the top!

and let him know to degrease the interior before you

you would still be looking at a micro-fraction of the cost of a glass apparatus.




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[*] posted on 29-11-2003 at 05:29
wow!


what are you talkin of btw?

helix, compressor tank, hard to explain to a machinist.........

what is it?
diffusion pump?
nono.....
mercury?
tachyonen?
overenergy?
warpdrive?
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[*] posted on 29-11-2003 at 06:22


what about some antimatter?
it will annihilate the norml matter so leaving you with PERFECT vacuum, of course some virtual particles could be formed from the energy that is around, but if you are smart and do this at 0°K it won't be an issue.
:D




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DDTea
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[*] posted on 29-11-2003 at 07:23


I'm kind of following you... You're suggesting to find Machinist build a rather large and powerful vacuum pump. What would really be helpful is if you did a quick and dirty sketch for us in Paintbrush, because at the moment, my sleepy mind is not following very well.
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Hermes_Trismegistus
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[*] posted on 29-11-2003 at 11:57
BIG SIGH!!!


You guys know what a diffusion pump is!!!

From Wikipedia, the free encyclopedia.


Diffusion pumps use a high speed jet of fluid to direct residual gas molecules in the pump throat down into the bottom of the pump and out the exhaust. The high speed jet is generated by boiling the fluid (typically silicone oil) and directing the vapor through a multistage jet assembly. Often several jets are used in series to enhance the pumping action.

Unlike mechanical pumps, diffusion pumps have no moving parts and as a result are quite durable and reliable. They can function over pressures ranging from about 10-10 torr to about 10-2 torr. Diffusion pumps cannot discharge directly into the atmosphere, so a mechanical forepump is typically used to maintain an outlet pressure around 0.1 torr.

One major disadvantage of diffusion pumps is the tendency to backstream oil into the vacuum chamber. This oil can contaminate surfaces inside the chamber or upon contact with hot filaments or electrical discharges may result in carbonaceous or siliceous deposits. Due to backstreaming, diffusion pumps are not suitable for use with highly sensitive analytical equipment or other applications which require an extremely clean vacuum environment. Often cold traps and baffles are used to minimize backstreaming, although this results in some loss of pumping ability.
--------

also note that sophisticated multistage diffusion pumps with atomic scavengers have been able to pull repeatable vacuums in the range of 10 to the neg 21 torr

and some labs have claimed 10 to the neg 23 torr, although those results have been hotly contested (thats like one atom per meter cubed, or something equally ridiculous!)

anyway the point is that you would be able to have a strong vacuum on tap which might be good for ambient temp fractional distilliation/sublimation of some of these energetic compounds you guys keep talking about/

and perhaps you could use the "unused" vacuum to regenerate your drierite?

whatcha think?.... McGyver's and McGyvette's!

[Edited on 29-11-2003 by Hermes_Trismegistus]

diffusion Pump.gif - 24kB




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[*] posted on 1-12-2003 at 08:03
Jesus!


That pump sounds a bit strong! Can you still keep your glassware in place with kekel clips and clamps? Just wouldn't want to crack a buchner and have it into the super-pump.

What is wrong with just a water aspirator on your faucet? How much vacuum do you need?

Oh, and one question: would the vaccum on this be strong enough to use to evacuate gas from a home-made fume hood and then out the window via tubing?




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[*] posted on 1-12-2003 at 13:26
diffusion pumps


need a forepump to work. Usually a rotary vain or diaphragm pump are used for this work - under some circumstances a aspirator may be able to provide enough vacuum - mostly not.
Usually mercury is used in diffusion pumps what resembles another problem because of the rather large amounts needed and the inherent dangers of mercury in gaseous state.

As soon I am able to loadup something again I can provide some information on this if there is interest.

The best diffusion pump known to me, the Gaede-4-stage, works against a pressure of 40torr - and beats by doing so all concurrency by miles. So a source of at least 40torr vacuum is needed. If you can afford the Gaede - I cant.




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[*] posted on 1-12-2003 at 14:54


Most diff pumps use oil, partly because of the problems with mercury, partly because with a synthetic oil you can tune its properties.
With a vac of 10^-23 torr you would run into problems with cosmic rays. It is several orders of magnitude better than they estimate for interstellar space. How do they claim to measure a vacuum that good?

[Edited on 1-12-2003 by unionised]
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Hermes_Trismegistus
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[*] posted on 23-12-2003 at 01:24


Quote:
Originally posted by jubrail
That pump sounds a bit strong!

What is wrong with just a water aspirator on your faucet? How much vacuum do you need?

Oh, and one question: would the vaccum on this be strong enough to use to evacuate gas from a home-made fume hood and then out the window via tubing?


YUP! actually it would be strong enough to evacuate your whole damn fume hood out of your window via tubing, but it's not really for such an application, you may simply want to use a squirrel cage blower for something so easy.

the purpose I think such a pump would be good for would be to lower pressure quite a bit more substantially than that afforded by a duo-seal mechanical pump.

like say you wanted to distill high boiling fractions in AMBIENT temperatures, with a diffusion....I am sure you could boil water with the heat of your hand and such.

Lets say you wanted to distill a temp sensitive product (like nitroglycerin) it would be nice to do so without adding heat wouldn't it?

I am not an explosives guy, but I am certain high vacuums could provide HOURS of fun for many the amateur scientist (if not always practical)


Its just that I see them up for auction frequently on labx and they look soooo tempting and pretty :o

sooo PRECIOUSSsss, my preaashezzzzz!!




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[*] posted on 23-12-2003 at 10:29


This entire thread went very odd early on.

Ultrahigh vaccuum doesnt put much more force on glassware than an ordinary aspirator.

You cant evacuate a fume hood with a diffusion pump through a tube becuase fume hoods require high volume, and diffusion pumps provide very minimal actual flow.

In terms of the cheapest method to high vacuum theres one method that simply cannot be beat,

A round bottomed flask full of acivated charcol or molecular sieve and a few litres of liquid nitrogen to cool the outside with. Now thats what I call a cheap and clean vaccuum. Supposed to work directly from atmospheric pressure too.
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[*] posted on 23-12-2003 at 12:37


Sci. Am. ran a few columns on vacum techniques just before the amatuer science column went under :mad:. Molecular sieves are recommended instead of activated charcoal unless you're trying to form an explosive.
BTW, I like the rotary vain pump. From the "Journal of Unpublished Chemistry":
Quote:
On the Use of Futyl Ester Prodrugs in Pharmaceutical Research.
Prodrug design to improve the absorption characteristics of drugs with carboxylate functionalities has explored numerous alkyl groups. Previously, methyl, ethyl, propyl and butyl have been the mainstay, our findings demonstrate that improved absorption can be obtained by using futanol to give the futyl ester. Attempts to use the invane sidechain for esters have proved in vain.
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[*] posted on 23-12-2003 at 15:28


A water aspirator will give a good enough vacuum to let you boil water with the heat from your hand.
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[*] posted on 23-12-2003 at 23:05


Quote:
Originally posted by unionised
A water aspirator will give a good enough vacuum to let you boil water with the heat from your hand.



DEAR GOD.....!?!

It must be that we are talking about different products here, When I think of a water aspirator I think of those dinky little twelve dollar items that pull less vacuum than my shop vac!

as for the molecular seives and LN2 I am all for any thing using those little things, since I found a good and cheap supply (aquarium supply), but here where I am peoples look sideways at you when you ask for a gallon of LN2 and I dunno how cheap that would be over time (repeatability) also you'd need a sizable legal dewar to pick it up in and then have to feel comfortable working with it on a regular basis.(I am very clumsy)

It seems a little neater on paper than after looking at the logistics.

and yes I too like the rotary vane pump, anything using such simple tech floats my boat. It would represent a good investment for someone who eventually wanted to move up to a diffusion pump because it could act as the required fore pump. In fact there is a matching combo for sale on Labx right now!




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[*] posted on 24-12-2003 at 04:51


No, Its the same thing. That farty little thing you hook up to the tap will drop the pressure to roughly the vapour pressure of the water running through it. (about 17mmHg for water at 20C).
Your hand can warm the water to about 30 to 35 C so the vapour pressure is about twice as high.
Even if the pump is not working to it's theoretical limit it is quite possible to boil water this way.
If you use one to pump the vapour off ether you can make ice.
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[*] posted on 24-12-2003 at 10:39


Your logic is impeccable, Unionised. I think there I may be overpaying for my university education. , and Soooo... by running a medium with a much higher vapor pressure than water through the aspirator...like a heavy oil...sigh!:(

also, I have been meaning to ask you...Is your name related to a quip in an article Isaac Asimov wrote in the March 1963 issue of the Magazine of Fantasy and Science Fiction, "You Too Can Speak Gaelic"?:P




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[*] posted on 3-1-2004 at 08:59


No. My name is just a nice chemistry related ambiguity.
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[*] posted on 16-8-2004 at 09:53
Vacuum on the Cheap: the Refrigerator Compressor?


http://www.belljar.net/refrig.htm



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[*] posted on 21-9-2004 at 20:52


a freezer works better,try looking for a walk in unit thats getting trashed from a old dinner. some units pull down a lot of vac. just think bigger ..ok 440 3phase might be a little much but hey.



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[*] posted on 22-9-2004 at 13:15
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Well sir; I'll admit when I'm being educated.

I am still trying to figure out the practical aspects of how to make the conversion from refridgerator compressor to vacuum pump and had to buy a small commercial version in the interim.

I have so many questions about these freezer compressors that I don't know where to start.

How did you convert yours?

H Tris.




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[*] posted on 23-9-2004 at 17:10


What would be the capacity of such a strong diffusion pump 10-21 torr? I would guess it would be able to pull a large volume or no? Would it differ based on the size of the gaseous oil jet being pumped through?
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[*] posted on 23-9-2004 at 17:48


Quote:
Originally posted by Mendeleev
What would be the capacity of such a strong diffusion pump 10-21 torr? I would guess it would be able to pull a large volume or no? Would it differ based on the size of the gaseous oil jet being pumped through?


Mendeleev; re-Diffusion Pump, I have done a little research on this, but no more than perhaps three hours total.

From what I understand of the diffusion pump, the answer is about capacity is both yes and no.:D

Yes it does "exhaust" an amazingly large "volume", but since most only seem to be designed to begin work at pressures less than 1mmHg, (they require a mechanical forepump), it might not really add up to that much in the total mass of air moved. (moving hundreds of litres of almost total vacuum per minute is almost a peculiar concept to grasp intuitively)

and yes, bigger pump, bigger volume.

P.S. I have since found out that most common metals are pretty much totally unsuitable for making serious diffusion pumps, not only do they carry one helluva load of absorbed....?.adsorbed....?, aw fuckit....I can't remember...

Anyway, the gasses come out slowly out of the metal when you pull a high vacuum and kill your vaccuum. Metals can also be somewhat permeable to some enviornmental gases, most notably, stray helium atoms.

However, glass can be fairly easily "de-gassed". By strong heating and other means.




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[*] posted on 23-9-2004 at 18:28


Just out of curosity what kind of pump would a professional lab use for a high vacuum? i can already guess that they must be pretty pricey
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[*] posted on 24-9-2004 at 02:25


Quote:
Originally posted by rift valley
Just out of curosity what kind of pump would a professional lab use for a high vacuum? i can already guess that they must be pretty pricey


depends how high a vacuum and what sphere of science.

Pro Chemical labs seem to use almost everything water aspirators, piston pumps, diaphram pumps, and rotary vanes. (application dependant)

Serious physics labs tend to go directly to multiple rotary vane pumps hooked in series with multiple stage diffusion pumps.

Those physics boys certainly do like to be vacuous.:D




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[*] posted on 24-9-2004 at 02:30


I think that they use mechanical vacuum pumps. They can get a better vacuum than aspirators and require no water, but they do require cold traps and expensive pump oil, not to mention other maintenance.

Just a thought on uber-high vacuums: if the material your apparatus was made of was an alpa-emitter, your vacuum would keep getting contaminated with helium!
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[*] posted on 24-9-2004 at 05:32


Industry uses liquid ring pumps as forepump and turbomolecular pumps for the high and ultrahigh vacuum needed for example for the manufacturing of microchips.

Nothing for at home though.




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