nannah - 22-7-2014 at 10:25
Hi, i am thinking about getting a vacuum pump, and would like to ask your opinion about this one i found on ebay? I will use it for distillation,
filtration. Basic stuff.
What CFM's, psi's and stuff like that should i look for?
Will this one do? Probably not, but it is cheap, and the shipping is free. 
http://m.ebay.co.uk/itm/321441411736?nav=SEARCH
Thanks in advance. /Nannah.
Burner - 22-7-2014 at 11:49
You might want to consider a water aspirator - good to about 25mm Hg (http://www.ebay.co.uk/itm/Waterbed-Drain-Venturi-Pump-/29118...)
Magpie - 22-7-2014 at 11:59
This looks like the typical Chinese made vacuum pump intended for use in air conditioner service. In the US they are commonly peddled by Harbor
Freight.
I have one rated at 2.5 cfm. I use it for vacuum distillations. Whatever you use it for you have to first consider what vapors might enter the pump
and contaminate your oil. If the vapors are going to mix more or less harmlessly with the oil then it's no big deal. But if they are NOx/HNO3 or
other such vapors then the metal pump wetted parts as well as the oil will likely incur severe contamination/corrosion. If this happens an immediate
oil flush/changeout would be required to save the pump.
If a cold trap is used ahead of the pump to condense out the noxious vapors then this will prevent or mitigate any pump/oil damage.
For Buchner filtrations and NOx I use my water driven aspirator instead of my vacuum pump.
In summary, it's a good choice as long as you understand its limitations.
Haber - 22-7-2014 at 12:26
Is there any advantage to use an stage 2 rotary pump instead of an cheaper stage 1 when it comes to vacuum distillations?
How big might the difference in vacuum achieved be?
Magpie - 22-7-2014 at 13:22
I get down to 2 mmHg absolute with my 1 stage $100 pump. For general chemical use this is more than sufficient.