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Fyndium
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Posts: 1192
Registered: 12-7-2020
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Is two phase vacuum pump overkill for distillation vacuum? For what types of distillations people generally use two phases? The price difference
between the two in ebay is so small I'd consider one.
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Dr.Bob
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Registered: 26-1-2011
Location: USA - NC
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Depends on the bp of the distillate. If you are distilling something that boils at 150 C at STP, then a simple vacuum pump might work fine. If you
are trying to distill something with a bp of 250C, then you may need to get a better pump. Like cars, the ability of a pump is not linear with
price, so paying 10 times more does not get you a 10X better vacuum, but might get you a mixture of higher vacuum, more capacity, and longer lifetime.
So you have to comparison shop and find the best deal for what you are doing. Most people won't need a 2 stage pump unless doing some serious work
or high BP distillation. But it will take an hour or more to do one, so the pump needs to work that long before it overheats or breaks. I have
seen some where I was not confident that it would last that long-I would skip those discount models, you need one rated for continuous use.
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Fyndium
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Posts: 1192
Registered: 12-7-2020
Location: Not in USA
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I have aspirator and 1-stage pump, and the 1-stage has been somewhat decent, but I was thinking if I need to distill some 200C+ bp liquids, I could
use the 2-stage for them. I'm not sure if they are suited for very long runs, the pump I already have sometimes makes occasional "chokes" when I run
it for more than hour, but other than that it doen't seem to take itself. It heats as all electric motors, but being only warm to touch it should just
do it's thing.
Only thing I'm worried as how to protect the pump from all kinds of contaminants. If there are any solvents, acids or something else the pump doesn't
like it. A method could be to strip lower bp residues with aspirator and then procceed to 2-stage when nothing comes over. I only can use CaCl2 ice
bath at 30-35 minus C for cold trap.
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RogueRose
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Posts: 1585
Registered: 16-6-2014
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I just got done using a $200 vacuum pump from Autozone and it performed FAR worse than any of the 4 compressors I took old AC's, heat pumps,
dehumidifiers, etc. The lowest the $200 pump could get was -25 or -26mm Hg while the compressors/pumps could pull down to -27 to -28.5 and they were
all FREE! I'd be really interested in if there would be any benefit putting all of these in parallel, or in some kind of series/parallel mix to see
if I can get an even greater reduction in pressure.
These are great for filtering liquids and ther may be some issues with vapors getting into the compressor, but you can put a dryer or AC in front of
the pump among numberous other things. I never did this though and they are still going strong for 5-10 years.
You can pick these up for $5-10 from some appliance scrappers, places that sell/service appliances, HVAC, craigslist, etc. I see no reason to spend
the $$ on a real vacuum pump unless you need to get down to micron levels (below 50 microns that is) , which will probably cost you $800-$5000+ for a
pump that can do that.
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