madcease
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vacuum pump decision
Hey guys i got 2 pumps i have in mind of buying but im not sure which one is more convenient for lab use can you guys have a look at these 2 ones 1.5
CFM the other 8CFM.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&Item
=200256629925&Category=1504&_trksid=p3907.m29
http://cgi.ebay.com.au/Vacuum-Pump-Javac-CS-40-
New_W0QQitemZ260291003403QQihZ016QQcategory
Z105778QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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madcease
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http://cgi.ebay.com.au/Vacuum-Pump-Javac-CS-40-New_W0QQitemZ...
http://cgi.ebay.com.au/NEW-REFRIGERATION-AIR-CONDITIONING-VA...
sorry thats easier 
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Magpie
lab constructor
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I have little experience with a vacuum pump but when I was considering buying one I didn't see why I would need one larger than 1.5 SCFM for lab use.
I think the larger ones are useful to refrigeration techs as they have to evacuate piping systems.
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chemrox
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I don 't think either of those pumps are very good for chemistry work and are too expensive for what they are. You can buy a very good used pump for
not a lot of money if you wait and search a little. Get a two stage pump designed for science as opposed to refrigeration or automotive work.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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stoichiometric_steve
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those pumps are good, unless used without a vapor trap (CO2/Acetone).
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franklyn
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Apart from bee like visits here , does anyone actually check
for previously posted info. Look close , except for capacity
it's the same pump !
http://www.sciencemadness.org/talk/viewthread.php?tid=10978
.
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chemrox
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we should check and we should search first for what the SE is worth. I rarely disagree with stoich but I think those pumps are lousy deals and he'll
want something better soon enough. You can use those for a lot of distillations and filtration but you can't use them for really low pressure
distillation and the main thing is you can get such good ones used for less than he's going to spend on the single stage jobs. I got my Welch 1400
Duo-seal for $25 and shipping.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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garage chemist
chemical wizard
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What kind of work do you intend to use the pump for?
If there is ANY chance of corrosive vapors, like HCl or HNO3, occuring in your apparatus, a rotary vane pump like the one you linked to on ebay is
absolutely unsuitable!
You HAVE to use a chemically resistant membrane pump, preferrably a two-stage one, for such work.
Recently, I and another fellow chemist bought such a pump as a component of a complete "pump stand" containing a digital vacuum controller with
manometer and magnet valves and a solvent recovery system on the output side of the pump that allows recovering volatile solvents without having to
use dry ice for cooling.
The medium to be pumped only comes in contact with PTFE inside the pump and any kind of aggressive vapor can be pumped.
It was an investment of EUR 500 (from ebay, it would have cost EUR 2500 if we had bought it new), probably the best one we ever did.
I will post pictures of this fine piece of equipment soon.
[Edited on 26-9-2008 by garage chemist]
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madcease
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Thanks for all your input. I think for distillations of things that dont contain HCL or and other acid or base should be fine with this.
Chemrox why do you say with low pressure distillations it is not suitable?
Cant a controller of some sort take care of that to lower vacuum.
How much do you think the MM Hg would be using that 4.2cfm pump?
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madcease
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The 4.2cfm pump was bought and runs a great vacuum of about 25" Hg
I found that when under full vacuum the pump starts to smoke out the exhaust.
Im used to pumps spitting a bit of oil out but not to the extreme where it fills the place up with smoke.
Is there a problem with the pump? Oil level was checked and thats fine.
I was thinking maybe a bucket of water with hose attaced from exhaust in there but scared it might draw back water into the oil contaminating even
worse.
Even ghetto pumps from a fridge worked better than this.
Got me buggered
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2bestyle
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| Quote: |
Im used to pumps spitting a bit of oil out but not to the extreme where it fills the place up with smoke. |
Thats absolutly normal for an oil pump, because the oil gets warm. You need an oil mist filter when you run the pump over a longer time.
A Oil pump you should never practice without cooiling trap, because the substance you destillate will get into the oil and will degrade your vacuum
and even water can corrode your rotary valve.
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