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Magpie
lab constructor
Posts: 5939
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Location: USA
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Mood: Chemistry: the subtle science.
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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]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Maya
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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
\"Prefiero ser yo extranjero en otras patrias, a serlo en la mia\"
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MargaretThatcher
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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.
The reformative effect of punishment is a belief that dies hard, I think, because it is so satisfying to our sadistic impulses. - Bertrand Russell
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chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
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vacuum pumps
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
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chemrox
International Hazard
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calculator
http://www.anver.com/document/company/Reference%20Guides/vac...
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Maya
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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
\"Prefiero ser yo extranjero en otras patrias, a serlo en la mia\"
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Sauron
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@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.)
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MadHatter
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Gauge
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]
From opening of NCIS New Orleans - It goes a BOOM ! BOOM ! BOOM ! MUHAHAHAHAHAHAHA !
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bio2
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.....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.
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Maya
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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.
\"Prefiero ser yo extranjero en otras patrias, a serlo en la mia\"
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Hilski
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| 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 $12 for another one ! |
I always had a hard time believing that those dinky little jet pumps could pull such a high vacuum. But now I am thoroughly convinced. I build one
the other day out of materials I already had, so it basically cost me nothing. Surprisingly, I was able to achieve about 30 torr with it. Today I
added a longer piece of hose to the outlet, and just like that it goes all the way to 13 torr! I could hardly believe that something so simple could
be so effective. And it doesn't get any cheaper than free.
\"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety. \"
- Benjamin Franklin
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Klute
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I was also very surprisd by this kind of system, would never had thought it could beat the big fridge compressor I had before... the compressor gave
~40mmHg.. I built a recirculating setup, with an out-water pump that has 35m max height (I dunno the term in english, approx 3.5bars pressure), it
cost me equivalent of 40$... 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
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tnhrbtnhb
Harmless
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Registered: 13-1-2007
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| Quote: | Originally posted by Hilski
| 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 $12 for another one ! |
I always had a hard time believing that those dinky little jet pumps could pull such a high vacuum. But now I am thoroughly convinced. I build one
the other day out of materials I already had, so it basically cost me nothing. Surprisingly, I was able to achieve about 30 torr with it. Today I
added a longer piece of hose to the outlet, and just like that it goes all the way to 13 torr! I could hardly believe that something so simple could
be so effective. And it doesn't get any cheaper than free. |
What stuff did you use, parts etc.? What pressure was the water input?
BTW everyone, I just won an ebay auction for a bunch (7) vacuum gauges, that measure from 0 - 760 torr. But, I only need 2 (1 and 1 for backup) so if
you want one of the other 5, I'll let them go for 7$ 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]
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Hilski
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| 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.
\"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety. \"
- Benjamin Franklin
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stoichiometric_steve
National Hazard
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dual aspirator setup?
referring to that eyela aspirator,
are the aspirators set up in parallel or in series?
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