Sciencemadness Discussion Board

Is there a solvent I can use to wash my vacuum pump oil reservoir?

Sidmadra - 29-5-2018 at 09:17

I've noticed with time there is colored material accumulated in my vacuum reservoir. I can only assume much of this is perhaps solvents that have oxidizer in the reservoir, or similar material. Changing the oil doesn't seem to clean most of this material out.

Would it be safe or effective to run a solvent like isopropanol or something similar through to clean this? I would use acetone, but would be concerned about chemical compatibility with any seals that may be inside.

Dr.Bob - 29-5-2018 at 12:56

The biggest issue with doing that is any solvent left in the pump can wreck it when you restart it. I would just put clean oil in it, run it for 24 hours under vacuum, and then drain that oil and replace. If the material does not dissolve in clean pump oil, then it is likely not hurting much. We have 20 year old Welch pumps that have black crap inside them, that still run fine.

If you take the pump apart to clean it, cleaning the metal parts in degreaser (TCE, PCE, DCM, hexanes, etc) is likely fine, which will remove much of the crud, but then you can make sure the parts are clean and dry before reasssmbling. The rubber seals are not good with most solvents, and alcohols and acetone will not likely dissolve the sludge, but might be OK with the rubber. But I have found that halogenated solvents are the best to dissolve the crap inside the pump, but only on the metal parts. And you don't want to clean the bearings with it, unless you completely clean and dry them and then regrease them.

coppercone - 29-5-2018 at 15:47

How do you degrease stuff like bearings? Use progressively lower boiling point solvents in a soxphlet?

Sidmadra - 29-5-2018 at 17:47

Quote: Originally posted by Dr.Bob  
If the material does not dissolve in clean pump oil, then it is likely not hurting much. We have 20 year old Welch pumps that have black crap inside them, that still run fine.


Well, I had a problem in the past where I just let gunk progressively build up in there, perhaps from letting old oil stay in there from too long, and the pump soon started to jam, stop rotating, and so on. It had some sort of mechanical failure relating to the pump housing and chemicals/residue in the oil. I was hoping to prevent that from happening again.

BromicAcid - 29-5-2018 at 18:24

Depends on what type of pump you have, what materials are in contact with the pump oil. The gaskets in there might not play nice with isopropanol. I've seen people flush the pump with solvent while the pump is running and collect it out of the exhaust. I've seen others remove the oil, replace it with a solvent, run the pump for awhile and suck out the oil with vacuum. In all cases the issue remains how to get ride of the residual solvents? I've seen some seal the pump and pull under vacuum to remove the solvents. Others refill with oil, run for awhile and toss the oil. Again, depends on the pump. Some manufacturers will specify how to 'power flush' their pump and their guidance should be followed.

alking - 30-5-2018 at 17:48

I've cleaned mine with DCM before and then let it sit outside in the sun to evaporate. I'd imagine ether would be even better, but I wouldn't want to waste it for that. I only do so because there's already DCM in there anyway so I figure it wouldn't be too acutely damaging to actually flush it with some. If you really want to get it clean you'll have to disassemble it, but I don't think it's really worth the work, vacuum pumps are cheap enough.

If you want to prolongue your vacuum pump's life you could also pickup a water pump and a water aspirator, you can use that for stripping solvents that would cause the most damage and then use the rotary for applications where you need a deeper vacuum.

Dr.Bob - 30-5-2018 at 17:55

DCM will kill the gaskets, seals, and metal in pumps, so don't let that get into the pump if possible. That (and TFA and other halogenated solvents) is one of the worst solvents to get inside a pump, which is why traps are good for them. If you try to rine it with a hydrocarbon, the pump can heat up enough to catch fire, which is exciting. Heard about it, never seen it myself, when fire shoots out the exhaust from too much hexane.

Degreasing parts is usually just soaking them in solvent; machine shops and auto supply stores sell various solvents for that. I try not to mess with the bearings unless they are really bad, but pushing new grease into them is almost always a good idea. There are tools for that, but a gloved hand also works.

If the pump is really bad, the only real solution is taking it apart, but we usually wait until it seizes to repair it, routine rebuilds are too expensive for most places, except on air plane engines. A good mechanical pump can be rebuilt several to many times unless really abused. Kinda like an old Ford 302, but simpler.

NeonPulse - 30-5-2018 at 21:32

I would agree that disassembly and cleaning the parts is probably the best way to get it clean. It’s what I’ve done a few times with my little 2 stage. Even though it was under $200 to buy (cheap as far as rotary vane vacuum pumps go) I still want to keep it in optimal condition. It is not as hard as I first thought it would be. Mine had actually seized after a few runs in which solvents and water with sodium hydroxide had been sucked into it. It was gunked up good.The fix was easy. Pull apart, degrease and re polish rusted surfaces with 1500 grit sandpaper and a dremel scotchbrite bit. Fresh oil in and off it goes again working as good as the first time it ran. Easy enough to do and it ensures that it will get a pretty long life.

Justin Blaise - 31-5-2018 at 04:43

In my lab we use flushing oil as part of our pump maintenance procedure. It's a lower viscosity oil that, I assume, is better able to dissolve and dislodged contaminants. We drain the old oil, then add the flushing oil, then run the pump for a couple minutes, then drain the flushing oil, and replace with new oil. It may not be able to get out baked-on tar, but it's been pretty effective at preventing its buildup for us.

It's a product similar to this one. We use Edward's brand, but that probably isn't important.

https://www.amazon.com/VacOil-Grade-Vacuum-Flushing-Fluid/dp...

alking - 31-5-2018 at 08:32

Quote: Originally posted by Dr.Bob  
DCM will kill the gaskets, seals, and metal in pumps, so don't let that get into the pump if possible. That (and TFA and other halogenated solvents) is one of the worst solvents to get inside a pump, which is why traps are good for them. If you try to rine it with a hydrocarbon, the pump can heat up enough to catch fire, which is exciting. Heard about it, never seen it myself, when fire shoots out the exhaust from too much hexane.

Degreasing parts is usually just soaking them in solvent; machine shops and auto supply stores sell various solvents for that. I try not to mess with the bearings unless they are really bad, but pushing new grease into them is almost always a good idea. There are tools for that, but a gloved hand also works.

If the pump is really bad, the only real solution is taking it apart, but we usually wait until it seizes to repair it, routine rebuilds are too expensive for most places, except on air plane engines. A good mechanical pump can be rebuilt several to many times unless really abused. Kinda like an old Ford 302, but simpler.


I agree, like I said I wouldn't use it if there wasn't already DCM in there. An ice bath trap isn't enough to capture it effectively and if I purchased some CO2 every time I'd be spending more on that than I have on the pump, and probably more for what my time is worth going to pick it up. I just get the cheapy pumps and accept that they will die one day. I should take my own advice and pickup a water aspirator setup to strip such things, but my pumps generally last a year or more so ~60$/yr isn't bad.

weilawei - 31-5-2018 at 10:13

A cylinder of CO2 for dry ice only costs me about $40 to fill, and the rental is about $50/year. That way I can run the pump as frequently as I want and avoid putting nasties into it.

alking - 1-6-2018 at 11:52

Exactly. A cheap rotary vane pump costs ~$60. Why would I spend 50$/yr and 40$ everytime I need to fill it when it costs less just to buy a new pump?

weilawei - 1-6-2018 at 12:47

Or buy a cylinder for 200$ and save 20$ every year? It pays for itself in 10 years if you use the absolute cheapest possible pump, but much faster if you use a nicer pump (say, two stages for a start). 2 stage pumps start around 130$, which already makes it cheaper to buy CO2/rent the cylinder. If you buy it, you break even in just under 27 months.

[Edited on 1-6-2018 by weilawei]

alking - 1-6-2018 at 13:17

Wouldn't you save 50/yr that way, where do you get 20? (nevermind, got in before your edit) However sure, but how many times do you refill your cylinder per year? 1.5 refills and you've paid for the pump, and that assumes the pump only lasts a year.

You're also expending electricity and additional equipment costs to freeze the CO2, how are you even doing so for that matter? Most of us don't have the equipment for that. Actually if you can freeze CO2 then why do you even need the CO2 to cool the trap in the first place?

If I wanted to protect an expensive higher end vacuum pump I simply woudn't use it to strip solvents and instead pickup a cheaper dedicated pump just for that, you can even get an aspirator setup and not have to worry about it eventually dying from corrosion/worn gaskets.

[Edited on 1-6-2018 by alking]

DavidJR - 1-6-2018 at 13:55

Quote: Originally posted by alking  
Wouldn't you save 50/yr that way, where do you get 20? (nevermind, got in before your edit) However sure, but how many times do you refill your cylinder per year? 1.5 refills and you've paid for the pump, and that assumes the pump only lasts a year.

You're also expending electricity and additional equipment costs to freeze the CO2, how are you even doing so for that matter? Most of us don't have the equipment for that. Actually if you can freeze CO2 then why do you even need the CO2 to cool the trap in the first place?

If I wanted to protect an expensive higher end vacuum pump I simply woudn't use it to strip solvents and instead pickup a cheaper dedicated pump just for that, you can even get an aspirator setup and not have to worry about it eventually dying from corrosion/worn gaskets.

[Edited on 1-6-2018 by alking]


You don’t need anything special to freeze CO2, all you need is, well, boyle’s law.

weilawei - 1-6-2018 at 16:02

Quote: Originally posted by alking  
Wouldn't you save 50/yr that way, where do you get 20? (nevermind, got in before your edit) However sure, but how many times do you refill your cylinder per year? 1.5 refills and you've paid for the pump, and that assumes the pump only lasts a year.


So far, it looks like perhaps 2x50 lb fills per year. I've been using the cylinder for about half a year now, or about 100lbs of CO2/year. My math did assume once a year, but I also make heavy use of it, for the cold trap as well as other cooling. I do also keep a dewar of chilled isopropanol, so I don't always need the dry ice.
Quote:
If I wanted to protect an expensive higher end vacuum pump I simply woudn't use it to strip solvents and instead pickup a cheaper dedicated pump just for that, you can even get an aspirator setup and not have to worry about it eventually dying from corrosion/worn gaskets.


You raise an excellent point, and this is in fact what I do. I have an aspirator, and that serves for stripping particularly obnoxious vapors (excessively low BP, highly corrosive, etc.). I won't use the pump for pulling bulk solvent out of something (drying a product is one thing, but I'd rather distill over solvent than force it through my pump). I frequently recover some small amount of product from my cold trap that might otherwise be lost. If it's not product, it's still something I don't want in my pump.

As to freezing CO2, my tank is filled with a liquid (gas headspace) and a siphon tube extends internally to the bottom. I use a small snow horn and pressure gage to blow the dry ice into a "sock" for collection. Just crack the valve and collect!

[Edited on 2-6-2018 by weilawei]