Sciencemadness Discussion Board - High vacuum CHEAP and dirty!

High vacuum CHEAP and dirty!

Hermes_Trismegistus - 28-11-2003 at 22:40

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.

wow!

Organikum - 29-11-2003 at 05:29

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?

Nevermore - 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.

DDTea - 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.

BIG SIGH!!!

Hermes_Trismegistus - 29-11-2003 at 11:57

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

Jesus!

jubrail - 1-12-2003 at 08:03

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?

diffusion pumps

Organikum - 1-12-2003 at 13:26

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.

unionised - 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]

Hermes_Trismegistus - 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

sooo PRECIOUSSsss, my preaashezzzzz!!

Marvin - 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.

Geomancer - 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.
DM, UK

unionised - 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.

Hermes_Trismegistus - 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!

unionised - 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.

Hermes_Trismegistus - 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"?

unionised - 3-1-2004 at 08:59

No. My name is just a nice chemistry related ambiguity.

Vacuum on the Cheap: the Refrigerator Compressor?

Democritus of Abdera - 16-8-2004 at 09:53

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

sarcosuchus - 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.

sarcosuchus

Hermes_Trismegistus - 22-9-2004 at 13:15

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.

Mendeleev - 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?

Hermes_Trismegistus - 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.

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.

rift valley - 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

Hermes_Trismegistus - 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.

neutrino - 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!

Organikum - 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.

Mendeleev - 24-9-2004 at 15:06

Yeah, them physics people love absolute vacuum, fictionless sufaces, and massless ropes and pulleys, etc

. The job of applying it to real world is up to the engineers. Also while looking wikipedia at that vacuum pump article you mentioned Hermes, I also found this:

Ion pump
From Wikipedia, the free encyclopedia.
Help us expand access to all human knowledge. Take part in our US$50,000 fundraising drive (http://wikimediafoundation.org/wiki/Fundraising).
We have crossed the $15,000 threshold! Still $35,000 to go!
Sputter ion pumps are a class of vacuum pump designed to operate in very low pressure (i.e. very high vacuum) conditions. They operate by ionizing a gas within a magnetically confined cold cathode discharge. The events that combine to enable pumping of gases under vacuum are:

Entrapment of electrons in orbit by a magnetic field.
Ionization of gas by collision with electrons.
Sputtering of titanium by ion bombardment.
Titanium gettering of active gases.
Pumping of heavy noble gases by ion burial.
Diffusion of hydrogen and helium into titanium.
Dissociation of complex molecules into simple ones for pumping ease, e.g., CH4 breaks down into C and 2H2. Hydrogen is pumped separately. Carbon is no longer part of the residual gas and resides in solid form.
Burial is the basic means of pumping heavy noble gases. Argon ions neutralized via glancing collisions with a sputter cathode impact the pump wall and are coated with sputtered titanium. Triode pumps are specially designed to maximize the kind of collisions that produce energetic neutrals.

Argon is permanently pumped on the wall behind the cathode in these pumps. The wall area receives titanium for inert gas burial but, because of a retarding electric field between the cathode and the wall, it is not subjected to ion bombardment and thus gases are not resputtered.

Not too shabby eh?

Jen - 8-11-2004 at 11:32

For electron microscopy which requires ultra-high vacuum we use a rotary pump for 'roughing', then a diffusion pump, and usually several ion getter pumps and a cold trap (running on LN2) to keep things going. The rotary pump is turned off when the pressure is low enough for the diffusion pump as it creates too much vibration.

http://lerch.no-ip.com/atm/Trap.htm - home-made cold trap, using Rp22 instead of liquid nitrogen as the coolant.

basicelectromechanic - 7-12-2004 at 15:08

As mentioned earlier by Democritus, the compressor from a junk refrigerator can be used as a cheap ( or free ) improvised vacuum pump. In my line of work we bench test used compressors and one that pulls a respectable vacuum against a test manifold ( and does not lose vacuum to discharge valve leakage after power is removed ) is considered fit for use.
This method will not pull a deep vacuum though, 50 to 80 torr ( 50 000 to 80 000 microns ) at best. Old beat compressors are not capable of pulling down like new due to piston to cylinder wear and valve wear.
With hermetic and semi hermetic pumps the vapor, lubricating oil and motor windings all are enclosed in the same space. Polyolester lubricant used with the newer HFC's is VERY hygroscopic. Long term use for this duty for which the pump was not designed will result in pump failure, particularly if you intend to vacuum distill strong acid, as this will atack the motor winding insulation resulting in " hermetic burnout ".As a short term cheap solution to a breif exercise where high vacuum is not required such a pump fits the bill.
For a deeper vacuum a two stage rotary in good maintain can pull 20 microns or better. Routine change of vacuum pump oil really makes a difference in ultimate vacuum achieved. Such pumps are available new from a refrigeration wholesaler or used and very cheap at auction.

If you intend to use an old compressor as a vacuum pump select one from your junkyard that has the start components attached and intact, if those components have been removed or disassembled odds are that the pump is failed. Also look at the paper or plastic label ( if present ) on the can, if it is browned instead of white this can has run at elevated temperature for a long time and should be passed by.
A compressor designed for use with R134 or R12 in a domestic unit will pull a deeper vacuum than one designed for use with R22 in an air conditioner. Coupling compressors together in series as shown on the previously mentioned website is not advisable, at high vacuum the motor winding insulation can fail.

[Edited on 7-12-2004 by basicelectromechanic]

Magpie - 12-12-2004 at 22:01

I am interested in buying a vacuum pump for common lab applications like filtering and vacuum distillation. Much of the previous discussion in this thread is about diffusion pumps and high vacuum. This seemed beyond my needs. So I have done some looking in catalogues. I soon realized that there are many types of pumps, even just for lab use. I felt I needed to establish my criteria, so, without much experience to base this on, here is what I have:

1. ultimate vacuum: 5-20 mm Hg absolute

2. noncondensable gas capacity: ~1 cfm

3. reasonably quiet

4. reasonably compact

5. relatively maintenance free

6. <$200

I think I'm reading that if I want to reliably get down to the vacuum of my criteria I will need a 2-stage pump. Then I must choose:

1. piston type, or
2. rotary vane

And then:

1. oil-less (PTFE/Kalrez), or
2. oil-filled

I would appreciate comments and recommendations, especially from those with some experience. If I have failed to list all needed criteria or missed some pump types, I'd like to hear about those too.

Even to meet my relatively modest needs it seems a new pump will be over $1000. This is beyond my budget. But there are a great deal of used pumps advertised on the internet for much less. I'm hoping I can get one for <$200 that won't require a rebuild right off the bat. Does this sound possible? Thanks for any help you can give.

Mendeleev - 12-12-2004 at 22:11

I would go to ebay. I got welch duo type vacuum pump for $75 1.2 cfm and a max vacuum of under 1 mm Hg. It's one of those old oil pumps that has a separate motor turning the pump using a rubber belt. It's not the prettiest pump but it gets the job done.

Magpie - 13-12-2004 at 22:43

Thank you Mendeleev. I have seen the Welch belt driven single stage pumps advertised. Apparently the belt drive provides low pump speed. This in turn allows reaching a 1 mmHg vacuum with only 1 stage. It also decreases pump wear.

It looks like selecting a lab vacuum pump is about as confusing as trying to decide what type of boat to buy. They all have their pros and cons.

I think it signigicant, however, that the mother of all lab supply houses only offers a 2-stage, oil-filled, direct drive pump (rotary vane I presume) for their "high" vacuum.

[Edited on 14-12-2004 by Magpie]

ADP - 3-6-2005 at 20:33

This is similar to a water jet vacuum I believe. I was wondering what type of vacuum one of these was able to pull. It is a pyrex type glass vacuum. 20 torr maybe?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=1...

Aspirator

MadHatter - 3-6-2005 at 22:20

Like any aspirator, it should pull down to the vapor pressure of water at 17 mm Hg (@ 20 C) as
Unionised stated in an earlier post.

ADP - 14-6-2005 at 08:06

Sorry for my ignorance but would a hand pump such as this one that produces 25inHg vacuum produce 634mmHg after you convert inches of Hg to mmHg? That seems like a really good vacuum for a hand pump. I was just wondering, the idea of vacuums interest me.

http://sciencekit.com/category.asp_Q_c_E_439390

neutrino - 14-6-2005 at 15:24

Yes. That does look like a good vacuum, but I doubt you could quickly evacuate something with 15cc strokes. Also remember the ridiculous price tag... I've seem better aspirators on ebay for <$2.

S.C. Wack - 14-6-2005 at 17:17

I got the same thing for much less a few years ago at Harbor Freight. Cynmar sells it for $20. $10 without the gauge. The second that I got it out of the plastic packaging, I noticed the flimsy handle and wondered how long it would last. Not long at all, it soon broke above the fulcrum despite some epoxy reinforcement. You get what you pay for. It is convenient for mobile application but a tire pump is at least less fragile.

Vacuum

MadHatter - 14-6-2005 at 20:47

I have a couple of those hand pumps. I find they're great for vaccum filtrations through
an Erlenmeyer flask, but for acid distillation you really do need an aspirator because of the
constant vacuum needed. I have a rotary vane pump(pulls down to 29" Hg) but I limit this
to air conditioning systems because acid vapours are quite corrosive. Stick with those cheap
little hydroaspirators for distillation work. There's not much(hydogen fluoride excepted) that
will hurt them. They're definitely worth the low price ! Besides, they'll wash any noxious
vapours down the drain as well.

For me price comparisons as follows:

Hand pump - $30
Hydroaspirator - $11
Rotary Vane pump - $200

It really depends upon your needs, but I'll stick with the hydoaspirator for most of my work !

[Edited on 15-6-2005 by MadHatter]

ADP - 20-6-2005 at 03:59

The only downside to a little hydroaspirator for vacuum distillation is the vacuum is pretty weak. It does have many pros, but is the weak vacuum it pulls really going to have a noticeable effect on the BP of the substance in your distillation setup?

unionised - 20-6-2005 at 12:37

Have you read the thread?
If so, did it occur to you that, if a water aspirator can drop the pressure to the vapour pressure of the water running through it, then it can boil water that is marginally warmer than that cold water?

ADP - 23-6-2005 at 15:20

Reread the thread, thanks for the help. I think I'll experiment with the hydroaspirator and examine the results.

S.C. Wack - 9-1-2009 at 18:57

http://books.google.com/books?id=msgAAAAAYAAJ&pg=PA77

This aspirator-assisted Sprengel pump, which recirculates the liquid mercury (not a novel idea, but a good design that one can improvise easily), makes me wish that I had some. The vacuum produced is on the order of vapor diffusion pumps. OMFG MERCURY! posts in 3,2,

watson.fawkes - 10-1-2009 at 08:14

Quote:

Originally posted by S.C. Wack
This aspirator-assisted Sprengel pump, which recirculates the liquid mercury (not a novel idea, but a good design that one can improvise easily), makes me wish that I had some. The vacuum produced is on the order of vapor diffusion pumps.

You could use the same basic design with an oil designed for a diffusion pump. It's not as dense, so your loop should probably be taller, but the same tuning principles apply. You'll need to find a tubing diameter than matches the surface tension of the oil. You need to adjust the head losses in the pumping loop (that's what the stopcocks are for) to get the right pulse widths of oil and gas. And there's less worry about containment, contamination, and cleanup.

Paddywhacker - 28-2-2009 at 16:58

Quote:

Originally posted by sarcosuchus
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.

Just cut the copper tubing with a hacksaw to vent the refrigerant (you wicked puppy!), cut the wires from inside the fridge and unbolt the compressor.

You will have to short out the wires that came from the thermostat, but that's not hard to figure.

Leave the compressor running for a few hours to purge it of lubricating oil, and there you have it... either a vacuum or a source of compressed air. The air might need a filter to catch entrained oil.

I've done toluene-based Dean & Starks that boiled from the heat of my hand.

[Edited on 1-3-2009 by Paddywhacker]

chemrox - 1-3-2009 at 01:42

I have a water aspirator, an aspirator pump, two, two vane mechanical pumps. My "high vacuum" requirement is 0.5 mm Hg. While an oil diffusion pump would help me get past some leaky connections, it is cheaper to track down the leaks and seal 'em up.
Cheers,
CRX

-jeffB - 4-3-2009 at 13:03

Quote:

Originally posted by watson.fawkes
You could use the same basic design with an oil designed for a diffusion pump. It's not as dense, so your loop should probably be taller, but the same tuning principles apply.

If I'm not mistaken, your loop will need to be something like fifteen times taller. Between that and the viscosity of the oil, it's not at all clear to me that this could be made to work.

It might be possible to make it work with indium-gallium eutectic, but that sticks to glass, and would probably be quite messy. It's also a lot more reactive than mercury, which could be a problem depending on what you're pumping down. And, of course, it's many times more expensive.

tryptamine - 7-3-2009 at 05:26

Quote:

Originally posted by chemrox
I have a water aspirator, an aspirator pump, two, two vane mechanical pumps. My "high vacuum" requirement is 0.5 mm Hg. While an oil diffusion pump would help me get past some leaky connections, it is cheaper to track down the leaks and seal 'em up.
Cheers,
CRX

A diffusion pump couldn't keep up with a leak anyways rox, they are for molecular scavenging to micro torr vacuum, and always require a good two stage roughing pump on the front end.

Air compressor into vacuum pump

Eclectic - 5-9-2009 at 16:56

or you can pick up a vacuum pump cheap at Harbor Freight.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnu...