Sciencemadness Discussion Board

Vacuum pumps

thunderfvck - 8-3-2004 at 21:22

Hello.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=2...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=38016...

I'm wondering if these two pumps would be satisfactory in terms of purifying nitric acid and filteration (I know the first link would filter fine, it's the same one we use at school). Would they also be good for any other vacuum-required procedures I may run into in the future? My limited experience inhibits me from being specific here, but I think you know what I mean. In a general sense. Also, if you had the choice, which would you choose?
Thank you!

[Edited on 9-3-2004 by thunderfvck]

vulture - 9-3-2004 at 01:02

First one. Oil pumps cannot be used for even slightly corrosive vapors, nitric acid will cause it to burn out in less than a few hours.

thunderfvck - 12-3-2004 at 23:27

You may be pleased to know that I am now the owner of the Barnet vacuum pump (the first link). Most excellent. $77.99 US was the closing bid. Brand new this baby costs $180 US. Gotta love ebay!

Vacuum gear

MadHatter - 21-12-2004 at 20:02

Various gear for various applications:

From left to right:

Rotary vane pump: air-conditioning
Hydroaspirator: acid distillations
Hand-held: filtrations

VPS.jpg - 138kB

Magpie - 22-12-2004 at 11:11

MadHatter has presented us a nice range of vacuum devices suitable for the home chemist, depending on application.

I have limited experience with vacuum use but have been giving it alot of study lately. I have some tentative conclusions that I would like to share:

1. If you have a hydroaspirator this will suffice for most lab applications as it will take you down to about 25 mmHg absolute. One must, however, keep in mind the 1st Law of Ecology: "Everything must go somewhere." So, if putting the evacuated gases/vapors down your drain is not a problem, you're set to go.

2. Mechanical vacuum pump selection takes you down a complex, branching path. These can provide "high vacuum," but who in the chemistry lab needs this? I'm talking in the micron range here, i.e., 1 micron = 10^-3 mmHg! This appears to be a toy for physicists. This is also where high cost comes in (>$1000). I think you are paying for equipment made to very fine tolerances.

For the chemists who needs to go below 1 mmHg absolute? Here you luck out as there is a wide selection of reasonably priced (<$200) vacuum pumps that are used by air-conditioning technicians. They use them to evacuate condenser coils before they load them with coolant (Freon, etc). These are typically oil-filled, rotary vane, 2-stage. But you just can't evacuate any shit into them. As Vulture has said acid vapors will ruin them. You also would not want to send a bunch of methylene chloride solvent into them. So, you have to pretreat the evacuated vapors by using cold traps, neutralization chambers, etc. You end up sending only inert gases like air through your pump. And then to be extra sure you change your pump oil if you have any doubts about its purity.

Note: All equipment in the vacuum train must be implosion proof!

So I don't see anything "cheap and dirty" about high vacuum. This rant is meant to get a discussion going so give me both barrels:P.

[Edited on 22-12-2004 by Magpie]

Rotary vane

MadHatter - 22-12-2004 at 18:48

Magpie, you mentioned "implosion proof". That's an excellent point. I wouldn't even think
of using the diaphragm or piston style vacuum pumps for anything that is even remotely
flammable.

My rotary vane pump is not nearly as noisy as I thought it would be. It's also pre-lubricated -
no oil to change ! The beast is heavy though - about 25 LBS. But for evacuating air-
conditioners it's excellent !

I find that the cheap little hydroaspirator is the best for lab work. It's great with acid
distillations because, as you previously stated, it washes those noxious fumes down
the drain. IIRC, I paid $9 for it. Now that's cheap vacuum !

For small, non-corrosive, filtrations through a funnel the hand-held from the auto parts
store works very well. It doesn't even object to hydrazine.

Magpie - 22-12-2004 at 19:24

I just past up the chance to buy a Ritchie Yellow Jacket, NIB, 2 cfm, 15 micron vacuum pump for $199. This is rotary vane, oil-filled, 2-stage. It's not that I don't think it was worth the price - I lusted after it mightily :(. I just couldn't justify it when I think that a hydroaspirator will fulfill 98% of my lab needs. Also, I will not have to deal with pretreatment of vapors - the more I thought about Dewars, dry ice, acid vapor neutralization, etc, the more I sobered up.

MadHatter - by implosion I mean violent vessel collapse. This is a serious safety issue with high vacuum (<25 mmHg) systems. If your glassware is not vacuum rated or is faulty, say has a star crack, it can implode. This event has the distinct possibility of making a mess of your hands, arms, face, etc. You would likely have to visit a doctor so that he could remove said shards.

[Edited on 23-12-2004 by Magpie]

Implosion

MadHatter - 24-12-2004 at 12:42

Magpie, sorry, I misunderstood what you were saying. I should have said "explosion". This
is something that would concern me with flammable solvents. Any diaphragm or piston
pump would scare the shit out me with those substances. On the topic of implosion, don't
use that cheap Bomex glass with vacuum. All of my filtration flasks are heavy-walled Kimax
or Pyrex and stand up well to vacuum applications.

neutrino - 24-12-2004 at 13:42

Quote:
Originally posted by Magpie
implosion...is a serious safety issue with high vacuum (<25 mmHg) systems

Wouldn’t the implosion problem be about the same for .001mm vacuums as 50mm vacuums? The only thing that matters is the pressure <i>difference</i>, right?

Magpie - 24-12-2004 at 20:23

Neutrino: yes. I don't think there would be any more risk with a "micron" pump than a 25 mmHg pump. I arbitrarily picked 25 mmHg, but just exactly at what vacuum a given piece of glassware fails would depend entirely on said piece of glassware.