Wizzard
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Pump not working correctly?
Recently purchased a damaged vacuum pump- ULVAC brand.
Pump had dirty oil in it, I've worked pumps before (hence the purchase of this broken one). Machine disassembled, and cleaned thoroughly- Reassembled,
now working BUT...
Pumps water down to boiling at about 55*F. I don't have an accurate vacuum gauge, so that's my measurement. It's expected to reach about 50 microns in
it's state.
2nd problem- The new oil went from a lovely pale yellow to a creamy white- What caused this? The pump has since become extremely difficult to turn,
and the motor will hardly move it- I've almost burned it out!
Any clues? The vacuum is small, and direct-drive, and I've used the correct oil and of course reassembled it correctly- I don't need an especially
high vacuum, just a functional one 
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unionised
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"The new oil went from a lovely pale yellow to a creamy white- What caused this?"
This
"Pumps water down to boiling at about 55*F."
Pumps don't like pumping water vapour, it ends up emulsified into the oil which raises the viscosity.
Flush out most of the buttery stuff, refill it with clean oil and then run it to drive out what's left.
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Wizzard
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Ah, should have figured... It's what I had thought, but I didn't imagine the water would have such a detrimental effect!! Once I emptied it out, it
became clear some of it was floating upwards- I'll let the oil settle overnight, see what it looks like. I have about 750mL of extra oil from my last
purchase, I just prefer not to waste it
Thanks for the confirmation.
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xwinorb
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I assume you have a rotary vane pump, looks like.
I strongly suggest to you to get a good electronic vacuum gauge. You can buy one for around $ 400.00, worth the price if you use your pump regularly.
Otherwise, it is difficult to know what your vacuum is at.
I have one HyVac rotary vane, one stage. After each distillation, the oil is usually white and opaque, like you saw yours. This is caused by solvent
and impurities and water dissolved ( emulsified ) in your oil. I think it is not worth trying to clean it, just change the oil.
Also, after use the vacuum should have degraded from say 0.8 mm Hg to anything from 2 - 20 mm Hg, depending on how dirty my pump oil is.
Best thing to do is to change it regularly, buy pump oil by the gallon.
Also, sometimes the vanes got stuck, don't move as they should, then your vacuum is very poor. This usually fixes after the pump warms up a bit,
sometimes you have to disassemble it and clean it.
It is a good idea to check what your pump vacuum is at before each distillation. My pump when clean and with clean oil reaches around 0.80 mm Hg. I
guess kind of typical of rotary vanes.
The figure you gave of 50 microns is a kind of theoretical number but I doubt any rotary vane to perform like that.
Another alternative is to use a cold trap, but it is not easy to do it.
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Contrabasso
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I know it's an odd concept but vac pumps are for pumping vacuum not solvent, in fact that's what kills them as you are discovering.
If you need to pump solvent (inc water) or corrosives (acid vapours) then you need to use a filter pump on a tap. This way you dispose of the carrier
medium without usually eating up the pump.
If you need the sort of vacuum that comes from vane or rotary pumps with diffusion pumps (do they still use boiling mercury?) then you must scrub the
vacuum free of anything that night contaminate or corrode the pump or it's oil
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xwinorb
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Forgot, also do not use BP of water to measure your vacuum pump vacuum. It is OK to use it for aspirators, but water vapor ( solvents vapors also )
and rotary vanes don't mix well as you saw.
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Wizzard
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Got it now It was actually 50/50 the emulsified oil, and a slightly
out-of-position motor... The bearing in the back also controls the phase of the motor- A mm or two in rotation greatly changes motor performance.
I ended up taking it apart again to clean it in full, I also managed to find the motor problem, and adjust the seals in the rotors to stop backflow of
oil into the vacuum. Seems to work very nice now
I've been considering buying a vacuum gauge, and $400 is a reasonable price, until one considers I purchased this pump for less than $75!!
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xwinorb
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Two links on vacuum gauges :
http://www.gaugestore.com/
http://www.tcvacuum.com/
I have the 500 model from JC, good one, from 0.01 mm Hg till 20 mm Hg.
I also use a course automotive vacuum gauge for my aspirator. Not so accurate but works. You could also use it to trouble shoot the vacuum pump
when/if it malfunction. This one costs around $ 25.00 only, but it is not accurate enough for low vacuum. Even at aspirator vacuum level it is not
very accurate.
Try Google also.
Looks like you did a good fix in your vaccum pump.
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tcfh
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Rotary vane pumps often have a gas ballast valve.
If you want to pump vapors of water or solvents (non corrosive), the pump should warm up for some time and the gas ballast valve should be opened a
bit, but the vacuum will not be as good as with completely closed valve.
It is also good for oil decontamination. When the oil is milky, decontaminate it by closing the entry of the pump and opening the gas ballast.
For this you should use a good oil filter, because there will be a fog of oil coming out of the pump.
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Wizzard
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Ah, mine has not a gas ballast- I had planned on heating the oil to about 80*C and then dumping it in a pan- Should remove most the water.
I've replaced the first batch of oil- Now the new oil I have in there is getting cloudy, from only removing semi-humid air from test tubes to be
evacuated 
Is it possible to retroactively install a gas ballast valve? Through 3 disassemblies, I'm very confident with the inner workings of my vacuum pump.
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tcfh
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This is how the gas ballast works:
h**p://userpage.chemie.fu-berlin.de/~tlehmann/gp/laborpraxis/oelpumpe/oelpumpe.gif
"Einlass" = Inlet, "Auslass" = Outlet
The gas ballast opening is in the cavity and I do not know, if it is possible to install a gas ballst valve to the inlet or without the danger to ruin
the pump by modification
You could dump the "wet" oil into a large jar and just add Na2SO4 or something like this and stir to dry it. It should get clear again and then filter
it with a Büchner funnel and paper or sintered glass disc. If the Na2SO4 particles are big enough a normal sieve should work very well.
Without a gas ballast you could install a cool trap with ice/salt or dry ice, or an absorber with a drying agent, that should not glue together.
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xwinorb
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I don't think ballasts are an effective way of outgassing water, solvents and other impurities in your pump oil.
I don' t think it is practical to try to clean dirty vacuum pump oil. It is lighter than water, but thick and difficult to filter I guess. If you wash
it you will have solvents and/or water mixed in with the oil, exactly what you want to get rid off.
Pump oil can be distilled but the BP is too high.
I would advise just clean your pump, get rid of any water left in the bottom and refill it with clean oil.
Check your pump and measure how it is performing regularly and before using it.
[Edited on 29-3-2010 by xwinorb]
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Wizzard
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Thanks for all the replies, guys I've got fresh oil in it again, and the oil
I've had sitting on the top shelf (the butter) has since cleared slightly- There is a transparent layer floating on top.
I think what I might try is evacuating a medium sized vessel (I have some nice canisters meant for this) filled with the oil- What this I HOPE will do
is cause the water to boil out and equalize the pressure, then I will heat it slightly, boiling out the rest of the water- When allowed to cool, and
the air let back into the container, the steam/vapor will condense and then settle across the TOP of the oil, as opposed to emulsified into it.
Step 2 would be just boil it at 100*C and see what happens
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tcfh
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I think it is quite useful to reuse "old" pump oil. If you do experiments with solvents or light corrosive gases/vapors you could use it once and dump
it out after the experiment.
Water is not a real problem in the pump, if it gets milky it is too much water and a cool trap should be a good idea.
I have a small rotary vane pump, which works perfectly at a rotary evaporator. After some time the pump gets warm enough that solvents do not solve
(only little) in the pump oil to affect the mechanical parts. The only effect is tha the end pressure is a bit higher.
If you pump vapors, even with only small quantities of corrosive gases (HCl,..) get the oil out of the pump because the steel parts get rusty.
And you could try to dry the oil with solid sulfates (Na2SO4), it is easier than heating the oil and it works. The solids settle on the bottom and
filtering is not necessary if you decant the oil carefully.
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Wizzard
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Ah, that I could do! I'll grab some sodium sulfate and hop on that I'd only ever
pump water throgh my pump, and even then I'm slightly concerned about rust!
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