Sciencemadness Discussion Board - cheap vacuum pump that can get down to 17 torr

cheap vacuum pump that can get down to 17 torr

tnhrbtnhb - 13-1-2007 at 06:17

How can I get or build a cheap vacuum pump that can get down to 17 torr (enough to boil water at 20 deg. C) ? I've searched this site and others, the best I can find is venturi pumps that pump down to 42 torr or so (28.3 inches Hg below atmospheric) (http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnu... .) I have a small air compressor with a resevoir, just for car tyres type thing.

I have asked on a hv/ac forum, and those guys say the vacuum pumps used in their industry only pull aka get below atmospheric by 29.9 "Hg, plus they cost some serious $.

They also tell me using a fridge compressor will not get below 150 torr.

Sauron - 13-1-2007 at 07:17

Get on to labx and stalk your wily vacuum there, a second hand PTFE diaphragm pump is what you want.

I got a little KNF Neuberger on there that according to the stickers came out of an SKF lab (Smith Kline & French.

I think I paid $150 for it.

Later I bought a new Gast rotary vane pump that I paid $800 for locally, not worth a damn, the ultimate vacuum is not as good as my Eyela dual asprator pump which pulls well under 20 torr.

[Edited on 13-1-2007 by Sauron]

MargaretThatcher - 13-1-2007 at 07:44

Quote:

Originally posted by tnhrbtnhb
I have asked on a hv/ac forum, and those guys say the vacuum pumps used in their industry only pull aka get below atmospheric by 29.9 "Hg, plus they cost some serious $.

They also tell me using a fridge compressor will not get below 150 torr.

ac vacuum pumps are generally 2-stage rotary pumps. They will pump down to much less than 1 torr. You can pick up second hand ones fairly cheaply. Change the oil if you need to get down to really low pressures.

It depends what sort of fridge compressor you have. You can still find some of the older rotary pumps that will get down to 1 torr or so in large freezers and air conditioners.

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

Magpie - 13-1-2007 at 14:28

Checkout the specs for the Yellowjacket line:

http://www.yellowjacket.com/PDF/SuperEvac_Vacuum_Pumps.pdf

They claim an absolute pressure of 15 microns. I believe a micron is 10E-6 mHg or 10E-3mmHg. So 15 microns would be equal to 0.015 torr.

These Yellowjackets are frequently found on ebay.

MargaretThatcher - 14-1-2007 at 06:42

Those yellowjackets are much favoured by those over the pond. Can't see if it has got an oil mist filter - those are important if you don't want to inhale the stuff (and you don't).

Sauron - 14-1-2007 at 06:58

Vacuum pumps are not all created equal. Some pumps types that are perfectly fine for purging a Ac or fridge prior to putting in new refrigerant are simply not at all a good idea for a lab.

The issues are not merely performance.

You have to consider exposure of pump materials to corrosive vapors, because you cannot count on your cold trap all the time.

You have to consider how different pump types handle flammable vapors.

Oil pumps are a pain.

And that is why I prefer to work with oil free PTFE diaphragm pumps. My fave is the Buchi V-500 series and esp the V1000 which is two V-500 set in series for high capacity or parallel for low ultimate pressure. Not cheap new but sometimes turn up on LabX or eBay. I also have a V805 digital vacuum controller which is very handy, sure beats a manometer and McLeod at least till you get down to very low pressures.

The KNF Neubergers are also very good.

MargaretThatcher - 14-1-2007 at 18:26

I think he is after something cheap that will pump down to 17 torr. To me, that gives 3 choices: 1. recirculating water-jet pump (US aspirator) with cold water; 2. 2nd hand oil rotary pump (heating engineer pump etc.); 3. homebrew rotary pump from old freezer or a/c unit.

For many, a 2nd hand air rotary pump is the best combination of price/performance with minimal construction effort. Water-jet pumps are a cheap way to put something together that is resistant to corrosive and high vapour pressure oil contaminants.

Yes, a PTFE diaphragm pump is great for certain jobs, just like a Bentley is for certain trips. If I had the spare cash to buy one, I'd spend it on something else.

Sauron - 14-1-2007 at 19:09

I got that KNF Neuberger PTFE diaphragm pump for $150

If you go see what the price is for a Nalgene aspirator (just a handful of plastic) it isn't that far off.

I used to use one of those. But Bangkok does not have cold water. My Eyela recirculating dual aspirator new cost me $800 plus another $400 or so for gauge and chiller tube.

So all in all I hardly think $150 for a 2nd hand PTFE pump is splurging.

Cheap and dirty often does not get the job done. An unsuitable pump that results in an exlosion when you evacuate say, ether, or that gets corroded to death when evacuating say, HCl gas, to cite two frequent applications, are not much of anyone's bargain.

S.C. Wack - 14-1-2007 at 19:57

Quote:

Originally posted by Sauron
I got that KNF Neuberger PTFE diaphragm pump for $150

If you go see what the price is for a Nalgene aspirator (just a handful of plastic) it isn't that far off.

OK...*goes to www.nalgenelabware.com*...they're $11.27 each, in a case of 24. Cole-Parmer sells them for $12.40 for a single one.

Vacuum Gear

MadHatter - 14-1-2007 at 22:23

A picture of my vacuum gear is in this thread:
(4th post in thread)

http://www.sciencemadness.org/talk/viewthread.php?tid=1649#p...

IMHO, for most applications in chemistry, the hydroaspirator is still the best vacuum source.
Pulls a decent vacuum, cost effective, and washes many nasty fumes down the drain.
If mine goes up I'll pay the $12 for another one !

An example of water vapor pressures at given temperatures:

SELECT VAPOR PRESSURES OF WATER:
UNDERLINES USED TO MAINTAIN SPACING
KPA VALUES FROM CRC 85TH PAGE 6-8

_C__/_____F__/______KPA__/____TORR__/__HG(INCHES)

_0__/__32.0__/____.61129__/___4.585__/__29.74
_1__/__33.8__/____.65716__/___4.929__/__29.727
_2__/__35.6__/____.70605__/___5.295__/__29.712
_3__/__37.4__/____.75813__/___5.686__/__29.697
_4__/__39.2__/____.81359__/___6.102__/__29.681
_5__/__41.0__/____.87260__/___6.545__/__29.663
10__/__50.0__/___1.22810__/___9.211__/__29.558
15__/__59.0__/___1.70560__/__12.793__/__29.417
20__/__68.0__/___2.33880__/__17.542__/__29.23
25__/__77.0__/___3.16900__/__23.769__/__28.985
30__/__86.0__/___4.24550__/__31.843__/__28.667

Sauron - 14-1-2007 at 22:29

And in Thailand where I am the Nalgene agent gets about $40 as they want to make a profit and the import duty on plastic products is high for protectionist reasons.

I have used a Nalgene aspirator before here, with municipal water supply which is rather warm and indifferent results but adequate to evacuate a three liter rotavap.

Also used a pricier Nalgene hand vacuum pump with a gauge, local agent did not stock the gaugeless version, that one DID cost me about as much as the KNF Neuberger, of course I got a lot of useful hand exercise out of it.

I still liked the KNF better, although it was US voltage and I had to run it off of a stepdown transformer.

I seem to recall plans for building your own Siibata or Eyela style recirculating aspirator, single or dual, on Rhodium. That would be a simple project for the non-craft challenged (craft nonchallenged I mean) requiring a plastic tank with a lid, a sump, two asprators, and some tubing. Add icewater and away you go. That will get you <17 torr for cheap. You might want to throw in some ice once in a while, provide for overflow, and change the water every few days before it starts to stink or before accumulated acids can corrode anything.

I elected to throw money at the problem just because I have more of that than time and patience for DIY projects.

Sauron - 14-1-2007 at 22:38

If anyone is interested I can scan and put up the illustrated manual for my Eyela dual recirculating aspirator with accessories.

Much better illustrations than the DIY piece on Rhodium. The Eyela asprators are plated steel but no reason why the Nalgene jobs would not do.

Costliest component will be finding a sump (submersible electric pump) with right capacity. Hit eBay.

Let me know if anyone wants this.

[Edited on 15-1-2007 by Sauron]

A1000S.jpg - 16kB

Sauron - 14-1-2007 at 23:38

I am not suggesting that anyone do what I did but rather than you build your own for a small fraction of the selling price of the commercial one.'

The pump on this A1000S has 150W output power and it has more than enough displacement to keep two aspirators happy.

If the water is cold (5 C) this unit will achieve 13 torr. By my own experience its displacement is quite good. It is oretty much a copt of the Siibata model which Buchi used to sell under their own name.

Note that the two independent asprator ports can be joined with a simple Y-adapter to make a single vacuum line, or you can evacuate two systems at same time.

There's an overflow valve so you can just keep chucking in ice to maintain low water temperature. Or if you have a recirculating chiller to cool your condenser, you insert an optional cooling coil and plunb it inline. As my local mains water is warm, I use a chiller for this purpose.

Sauron - 14-1-2007 at 23:56

@S.C.Wack, this is OT but you mentioned Cole Parmer. I have their full catalog as well as their Encyclopedia Microflex.

I have bought from their local agent for years.

Recently I imported a Labconco glove box with gloves from USA second hand. It was properly declared and it included a pair of neoprene glove box gloves/gauntlets. US Customs did not require any special paperwork at all and neither did Customs here.

The gloves were old and needed to be replaced so I looked them up in Cole Parmer, expensive but what the hell. I got a bargain on the box and it is useless without gloves.

I ordered them. Three months later I was still waiting. After a number of outright lies the agent finally told me Cole Parmer was waiting for an EXPORT LICENSE approval from the US Government.

I'm a US citizen in a country that's a US major non-NATO ally (MNNA). It's a pair of ordinary neoprene gloves. I got mad and cancelled the order.

And now am looking for a vendor that is in a country that does not have its head up its ass.

The obstructing agency is the Commerce Department, the State and Defense Depts do not care.

What BS!

quicksilver - 17-1-2007 at 17:11

I know this is a bit OT but does Thailand import from mainland China? There must be a boatload of labware concerns made in China....

MargaretThatcher - 17-1-2007 at 17:17

I would have thought that Thailand itself would have some pretty good on-going concerns, especially for a resident Yank.

Sauron - 17-1-2007 at 17:22

@Maggie, please explain what you mean by your comment.

Do you mean that I should be worried about Thailand or vice versa?

Actually the answer is neither.

What are your concerns about Thailand? A very safe place for Thais and expats alike.

MargaretThatcher - 18-1-2007 at 04:38

I don't mean dangerous, I mean readily available lab. equipment and for a good price. I found a good outlet a while back in Bangkok.

I agree that it is a very safe and nice country.

(Edit: concern = business)

[Edited on 18-1-2007 by MargaretThatcher]

Sauron - 18-1-2007 at 05:25

@Mrs. T., sorry, I misunderstood.

Lab equipment companies in Bangkok are usually happy to do business with anyone with a local corporation or other form of business entity and not too happy about individuals. I do have a corporation, and am thinking about setting up a not for profit foundation for chemical research and education. It takes a million Thai baht ($20,000 US and change) cash or equivalent in goos, I have a lot more than that worth of lab equipment and chemicals. It takes ten people to form such a foundation and it has to be vetted by the National Culture Ministry and the Special Branch of the National Police but that is not a big problem. I've got appropriate people for that including a recent Thai chemist retiree from the National Research Council.

Vacuum Gauge

MadHatter - 18-1-2007 at 07:32

Sauron, that's cool if you can get a non-profit group setup. If it means easier access to
what you need it's well worth it IMHO. It sounds like, that beyond the initial vetting,
you'll have few, if any, problems with the authorities.

Back on topic. I just ordered a laboratory grade vacuum gauge from eBay. It goes from
0 to 750 mm(Torr) Hg. The only other gauge I have is on an automotive vacuum pump.
It reads in inches Hg and kPa. I don't have faith in the accuracy of this device.
When connected to the hydroaspirator the gauge shows over 29 inches Hg being
pulled but I want a more accurate device, and in Torr.

The biggest problem I had with the hydroaspirator was setting up the combination
of adapters to run it off the kitchen faucet. There was no convenient faucet-to-1/4" barbed
adapter in the hardware store. I already had the faucet-to-garden hose(3/4") adapter.
Got that one to run my still !

So the combination of faucet-to-3/4", 3/4"-to-1/2",
1/2"-to1/4" barbed, all wrapped with teflon tape was the only OTC method available.
The cost was low even for brass fittings and less then the hydroaspirator.

The nosy cashier at Lowes asked me what all that was for. I told her I needed it for a chemistry
application that requires vacuum. She got a dumbfounded look on her face at that point
which I interpreted as "What a fucking geek !". Better than "terrorist" or "meth-cook" !

Sauron - 18-1-2007 at 07:40

@MadHatter, I suppose so! Actually I had the same problem (adapting aspirator to faucet). Fortunately here the machine shops work cheap so I just had an adapter made up out of brass hex stock. Still had trouble because water temp was never cold and in daytime was downright hot.

And that's why I went to other systems.

What brand is the vacuum gauge?

Maya - 18-1-2007 at 08:01

the automotive vacuum , or ac/ refrigeration pump gauges are really bad for accuracy

Best for me was the digital kind, SUPCO VG64 DIGITAL VACUUM GAUGE

0-12,000 microns claimed

Sauron - 18-1-2007 at 08:24

@Maya, sounds nice. I have a digital Buchi V805 purchased new for godawful price, it's not just a gauge but a controller with a microprocessor to run a valve. Intended primarily for rotavaps. The display is in torr or mPa or psi at your selection, Variable hysteresis, programmable controls. I hardly ever used the control aspects and didn't much care for the "automatic distillation" stuff, but as a gauge it is good but overpriced. This one is nomainally 220V but runs perfectly on 110 anyway. However it does not have a bottom end as low as the one you describe.

What sort of $$ is the Supco?

[Edited on 19-1-2007 by Sauron]

Maya - 18-1-2007 at 08:27

I picked it up new for $80 or so at a well known place that sells these things. but they usually retail double that

The J-Kem controllers looked nice to me for programmable solutions until I saw their prices, tho still reasonable for academic purposes

Bourdon

MadHatter - 18-1-2007 at 10:01

Here's a picture of it. It's analog but it has to be better than that automotive vacuum pump
gauge.

BOURDON.jpg - 13kB

Magpie - 18-1-2007 at 10:42

Very nice Madhatter.

For those looking for ideas on adapters for kitchen faucets which are typically fine threaded for aereators, here's what I made up. I don't use these anymore as I have my lab in my garage now. The upper chrome plated brass part is available at the hardware store as well as the lower brass adapters. I believe the left brass one is 1/2"FNPT x 3/8"FNPT and the right brass one is 1/2"FNPT x 1/4"FNPT. The two pieces are soldered together as you would copper pipe. It takes a little patience and trial & error but both of these are liquid tight.

Edit: corrected thread sizes

[Edited on 18-1-2007 by Magpie]

faucet adaptors.jpg - 48kB

Maya - 18-1-2007 at 10:44

NO, plain and simple.

I have pretty much the exact same one and when put on the same vacuum source with a digital , it turns out that the calibration and accuracy on the analog is WAY off. Prolly by an inch of mercury. I would build a mercury one again to compare the three but they are a pain

MargaretThatcher - 18-1-2007 at 16:19

Maya,

It is the quality of the gauge rather than whether it is analogue or digital that governs the accuracy and precision of its measurements. High quality mechanical gauges that operate in the required pressure region are available, but expensive. Most gauges measure gauge pressure, i.e., the pressure wrt surrounding atmospheric pressure. Absolute gauges, which measure pressure wrt vacuum are more expensive.

Gauge pressure varies around absolute pressure by an inch or so of Hg because atmospheric pressure changes all the time. Hence you cannot accurately measure pressures within a few inches Hg of absolute vacuum using gauge pressure unless you correct for atmospheric.

vacuum pumps

chemrox - 18-1-2007 at 18:16

I'd recommend a two stage mechanicl pump. Sometimes incredible deals are on the net. I got a seargent welch duo seal for $75 on ebay.

a good water pump and cold water can get you down to 30 torr

calculator

chemrox - 18-1-2007 at 18:18

http://www.anver.com/document/company/Reference%20Guides/vac...

Maya - 18-1-2007 at 18:33

M T

I would respectfully say that the most accurate method would be against a mercury manometer.

Of course you compensate for sea level , which I live at + 5 FEET, but otherwise analog is not a good instrument compared to digital for consistent and reproducible readings unless you want inaccurate results

Take my word, Build a mercury manometor and see the difference in accuracy with the analog model, it is a world of greater in telling you the actual pressure

Sauron - 18-1-2007 at 20:01

@Maya is right. I have used manometer + McLeod; good but a little kludgy and a lot of Hg around in fragile glass.

More recently oil McLeods have come on market but I never used one.

Remember McLeods have A B and C scales so if you work at really low pressures you need more than one McLeod.

And that mitigates in favor of a good digital gauge instead like the one @Maya is talking about.

$160 is very low cost for 0-12,000 micron.

I have maybe $1500 in my Buchi, admittedly a controller not just a gauge but it does not have a bottom end that low. I forget the details but probably nothing below 10 torr. And resolution is +/- 0.1 torr IIRC. The same goes I think for the JKEM unit Maya referred to.

I'd cheerfully spend $160 to add a digital unit with a very low pressure capability and avoid having to get involved with McLeods and manometers again. Go price a McLeod new and you will see why. (Aldrich, Ace, etc.)

Gauge

MadHatter - 19-1-2007 at 20:16

Right now, I'm going to be happy with something that shows me Torr. Digital gauge ? Maybe
later. I don't need something that goes into the micron range - at least not yet.
I'll agree that a mercury manometer is the most accurate, but quite expensive as
already stated.

I've often wondered if I could adapt the manometer off a wall-mounted sphygmomanometer
like the one my doctor measured my blood pressure with yesterday. Any thoughts ?

[Edited on 2007/1/20 by MadHatter]

bio2 - 19-1-2007 at 20:52

.....if I could adapt the manometer off a wall-mounted sphygmomanometer.............

I suppose you could seal one end and make a Bennert
closed end manometer.

Maya - 20-1-2007 at 01:31

I made one with some mercury, a long small diameter tube sealed at on end, a one holed stopper , and a test tube with a side arm outlet. Very accurate from 1-100 torr.

Hilski - 20-1-2007 at 15:28

Quote:

IMHO, for most applications in chemistry, the hydroaspirator is still the best vacuum source.
Pulls a decent vacuum, cost effective, and washes many nasty fumes down the drain.
If mine goes up I'll pay the $12 for another one !

I always had a hard time believing that those dinky little jet pumps could pull such a high vacuum. But now I am thoroughly convinced. I build one the other day out of materials I already had, so it basically cost me nothing. Surprisingly, I was able to achieve about 30 torr with it. Today I added a longer piece of hose to the outlet, and just like that it goes all the way to 13 torr! I could hardly believe that something so simple could be so effective. And it doesn't get any cheaper than free.

Klute - 24-1-2007 at 01:15

I was also very surprisd by this kind of system, would never had thought it could beat the big fridge compressor I had before... the compressor gave ~40mmHg.. I built a recirculating setup, with an out-water pump that has 35m max height (I dunno the term in english, approx 3.5bars pressure), it cost me equivalent of 40$... Before, I used an immerged pump, 7500L.H-1, but it could'nt give out a good pressure, and it heated the water up very quickly..... With my new big pump, I get <20mmHg, when using ice cold water (I haven't got a decent vacuum gauge, I just mesure the temp of a boiling liquid and convert... very approx that's sure, but I can reconize the Bp of the products I distill) Let's say that water boils vigorously at ambient temp, which is something like 5-10°C.. I can roughthly regulate the vacuum by opening a vanne in the water outup, before the aspirator, but this is quite tricky as it's not at all precise... in only a few degres change, you can passs from a very low flow to something powerfull.. Once I did the stupid mystake of closing the vanne slightly, and even if I had a one-way valve on the vacuum outlet of the aspirator, water can throught in the recivers...
One of the problems here is that water does heat up appreciably with such an water pump, and instead of having constantly ice in the reservoir, I leave it around 20°C, and change water regularly by placing the end of the aspirator in a big bucket, until 2/3 of the reservoir are emptyied, before air can be sucked up by aspiration of the water, and immediatly replace with fresh (5-10°C) water in another bucket. When doing that 2 times in a row, water goes down to 10°C, and I repeat this after 30min/1h depending on how much time the pump is been on.. Of course, this isn't the best thing to do if you want steady vacuum, but I get sharp boiling points anyway.. Just depends on the application and the amount of money and freezer place you are ready to give for ice

The whole setup cost me perhaps eq.50$, and is perfect for what i use it for... no hassle with acid or solvent fumes, as they are very diluted in water, which is frequently changed, good vacuum, but a little noisy, and changing water while the pump is working is quite messy, but WTF. IMHO, these devices are worth builing for someone with a little budget, and needing vacuum up to 15mmHg...
I still dream of those masssive vacuum pumps at night, though

tnhrbtnhb - 15-2-2007 at 16:43

Quote:

Originally posted by Hilski

Quote:

What stuff did you use, parts etc.? What pressure was the water input?

BTW everyone, I just won an ebay auction for a bunch (7) vacuum gauges, that measure from 0 - 760 torr. But, I only need 2 (1 and 1 for backup) so if you want one of the other 5, I'll let them go for 7$ plus shipping. Email me at idrcon ot yahoo.com. I looked for a FS section around here, I think one would be appropriate.

[Edited on 16-2-2007 by tnhrbtnhb]

[Edited on 16-2-2007 by tnhrbtnhb]

[Edited on 16-2-2007 by tnhrbtnhb]

[Edited on 16-2-2007 by tnhrbtnhb]

[Edited on 16-2-2007 by tnhrbtnhb]

[Edited on 16-2-2007 by tnhrbtnhb]

[Edited on 16-2-2007 by tnhrbtnhb]

vacuumgauge1and2.jpg - 95kB

Hilski - 15-2-2007 at 20:14

Quote:

What stuff did you use, parts etc.? What pressure was the water input?

I used a 3/8 inch steel tee (the kind used for black steel pipe) and for the inlet I used a 3/8 inch brass hose barb with a copper tube glued inside it with epoxy. The same type of threaded brass hose barb connectors were used for the water outlet and vaccuum outlet. I basically used the plans from Frogfot's website, along with some tips and info from threads here on SM.

dual aspirator setup?

stoichiometric_steve - 18-2-2007 at 23:59

referring to that eyela aspirator,

are the aspirators set up in parallel or in series?