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Author: Subject: Which vacuum pump ?
metalresearcher
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[*] posted on 5-11-2016 at 02:12
Which vacuum pump ?


I am looking for a vacuum pump for obtaining pressures preferably under 0.01 bar.
I found several on amazon.com for prices ranging from $100 to $300.
But no description of a pump tells the pressure to be obtained.
And are two stages pumps for a better vacuum ?

Does somebody know which is best ?

https://www.amazon.co.uk/dp/B0105UV508?psc=1
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Sulaiman
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[*] posted on 5-11-2016 at 05:50


What is significant about 0.01 bar ?

What do you want your vacuum pump for ?

I bought a dual stage rotary rated at 0.3 pa thinking that it must be more useful than the cheaper single stage 5 pa types ...
(1 bar = 100,000 pa, 0.01 bar = 10 pa =
http://www.ebay.co.uk/itm/New-2-5CFM-1-4HP-Single-Stage-Rota...
wrong !
there is virtually nothing in hobby chemistry that requires such low pressure,

for mollecular distillation and thermionics, a mean free path of 100mm requires a vacuum of 0.1 pa ... too low for my dual stage rotary
https://en.wikipedia.org/wiki/Mean_free_path

then there is the problem of contaminating the pump,
the HVAC pumps are iintended to handle a little water vapour,
but the oil and aluminium can be damaged by most things that we are likely to filter or distill.
And unobtainable (for the average hobbyist) low temperatures are required for even simple traps.

chemically resistant membrane/diaphragm pumps should cover most needs, but ultimate vacuum is not as good as a rotary.

IF I was starting again, knowing what I now know,
I still could not choose :)

I think that you should specify (to yourself) what you want the pump for ... not easy.

If you do go for a rotary
I believe that the cheaper pumps such as the one pointed to above are good value
... check the cost of parts or service for (for example) an Edwards pump.

Also, there are endless threads on this topic here at SM :)
and the pump that you pointed to has "15 Microns " in the description, 15 um = 0.015 mm (Hg) = 2 pa = not very good for a two stage rotary.
(better to buy a cheap 0.3 pa Chinese pump, even allowing for 'enhanced' advertising specifications)

[Edited on 5-11-2016 by Sulaiman]




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wg48
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[*] posted on 5-11-2016 at 07:44


Quote: Originally posted by metalresearcher  
snip
But no description of a pump tells the pressure to be obtained.


I guess you missed this in the description of that pump: "Ultimate Vacuum: 15 Microns" which is about 0.000,015 bar. So until the oil gets too contaminated or the pump too corroded or worn it will reach 0.01bar.

As the prevous poster suggested you need to know what you want from the pump and of cause what your willing to pay Reading the discriptions will help a lot too LOL.
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metalresearcher
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[*] posted on 5-11-2016 at 09:19


What I want to do with it ?
Vacuum distillations of aqueous solutions, low pressure experiments with water and ethanol.
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yobbo II
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[*] posted on 5-11-2016 at 11:21


Get an aspirator
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[*] posted on 5-11-2016 at 14:26


Yobbo is right.
Water kills most other pumps, and an aspirator will drop the pressure to the point where water boils so that's as good as you need.
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Mush
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[*] posted on 7-11-2016 at 09:46


This vacuum pump def suits your need. 49.99 GBP . I wouldn't buy an expensive one unless I'm a pro user.
http://www.ebay.co.uk/itm/like/1-4HP-5Pa-220V-50Hz-2-5CFM-Si...

[Edited on 7-11-2016 by Mush]
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[*] posted on 7-11-2016 at 11:47


Quote: Originally posted by Mush  
This vacuum pump def suits your need. 49.99 GBP . I wouldn't buy an expensive one unless I'm a pro user.
http://www.ebay.co.uk/itm/like/1-4HP-5Pa-220V-50Hz-2-5CFM-Si...

[Edited on 7-11-2016 by Mush]


That pump will suit your needs until it gets killed by the water vapour. It might last a year, but I'd bet on shorter than that.
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pineapplechunk
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[*] posted on 22-6-2017 at 10:26


http://www.ebay.com.au/itm/180W-Water-Circulating-Vacuum-Pum...

Thoughts on this. Is this like an expensive version of an aspirator?
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elementcollector1
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[*] posted on 22-6-2017 at 10:46


It's an aspirator with a fancy outer casing, really.



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cjacob
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[*] posted on 20-9-2017 at 02:45


Karlsson Robotics is a brand that produces good vacuum pumps, I am sure you will get a good one from this brand. Try searching on Amazon as well.
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