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The Plutonium Bunny
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[*] posted on 13-12-2024 at 21:26
Help fixing tar in vacuum pump


I just came into possession of an intact Varian SD 450 scientific grade vacuum pump (2-stage, 16 cfm, <1 mtorr ultimate pressure claim). The pump is very expensive new and would make a great roughing pump for some advanced experiments involving higher levels of vacuum, but there is one problem. What oil is in the pump has turned into a very thick tar, thick enough that it stands up on its own (see picture).

Is there any way on earth to rescue this pump? I imagine disassembly is necessary, but I'm not sure if there is a solvent for "vacuum pump oil tar". I haven't been able to find discussion of this issue elsewhere, but the oil/tar is the color of well-used motor oil, which leads me to believe this poor pump was abused in its past life. Interested in all suggestions!

IMG_6150.JPG - 1.4MB




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[*] posted on 14-12-2024 at 03:55


You’ll definitely want to disassemble it for a scenario like this. I’ve only repaired belt-driven Welch rotary vane pumps before. On my rotary pumps, I use flushing fluids you can buy to help intermittently remove sludge buildup during oil changes, but you’re well passed this stage on that pump though.

I actually found the manual for your pump:

https://www.ptbsales.com/media/productattach//s/d/sd-series....

And here’s the rebuild kit for your pump:

https://www.idealvac.com/en-us/Varian-SD450-Vacuum-Pump-Majo...

The website above makes great aftermarket repair kits for vacuums. For a lot of models they offer minor and major rebuild kits. You can look around to see if they have a minor rebuild kit for yours, as I only linked the major rebuild kit.

When I’ve rebuilt my Welch vacuums, all of the metal components would get soaked in petroleum ether, but a lot of solvents can substitute for this. There’s a chance your pump is ok and just needs a rebuild honestly. For how thick that sludge is, I’d imagine only attempting flushing fluid on this could harm the pump. You’ve probably got a mixture of degraded oil, contamination from not using a vacuum trap, and probably some metal particles in there.

In this manual, it shows a lot of the pump breakdown and mentions using “solvent” for cleaning parts, but nothing specifically except for “alcohol” being mentioned. Stuff like hexane, pet ether, and isopropanol should be more than suitable for removing all that sludge building. Not using wire brushes for cleaning rotary vane parts is a given. For stubborn gunk buildup, a soft, non-abrasive brush works fine. I have some cheap polypropylene soft bristle brushes I got on Amazon that I used for my rotary vane repairs.
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[*] posted on 14-12-2024 at 06:37


Quote: Originally posted by Eleutheria  
I’ve only repaired belt-driven Welch rotary vane pumps before. On my rotary pumps, I use flushing fluids you can buy to help intermittently remove sludge buildup during oil changes, but you’re well passed this stage on that pump though.


Those Welch pumps take a beating. I had one filled with methanol running on itself to help loosen up some garbage and one of my labmates unintentionally used it for a distillation, he was complaining to me that it was only pulling 50 mm and I said "That's pretty good for a pump that's using methanol in place of oil."

That being said a rebuild might put you in a good place to start. I don't know your particular pump, if you look though the specs and see that solvents won't hurt it though it might be worth a shot if the other option is a rebuild. It depends on the compatibility with the gaskets.




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[*] posted on 14-12-2024 at 07:51


Great, thank you for all the tips and sharing your experiences. I have taken apart some cheap pumps before during oil changes and have seen the sludge that sometimes builds up, and I don't even know if this pump has that. Last night I ended up taking off the oil reservoir (with much difficulty) and the entire charge of oil that was left in the pump (about 1/3 full) has polymerized, basically sticking everything together with its absurd viscosity. It's so bad that the oil polymer doesn't even stick to a bare finger, it just takes up a fingerprint.

I'll try some solvents and manual removal to get the oil tar out and report back. In any case, the pump itself is very stuck but the motor works on its own.




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[*] posted on 14-12-2024 at 08:00


What a nightmare. I’ve rebuilt a lot of pumps and never seen anything that bad. I would scrape off as much of the sludge as you can with a plastic putty knife first, then fully disassemble the parts and soak them in hexanes or pet ether as others have suggested, scrubbing with a soft bristle brush like an old toothbrush if necessary.



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[*] posted on 14-12-2024 at 09:30


I have a cheap HVAC pump that may need servicing,
I am considering petrol (standard RON95 from a pump) as the solvent due to cost,
any reason(s) to not use petrol/gasoline?




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[*] posted on 14-12-2024 at 16:55


Other than he stink and fire hazard. Petro/gasoline makes a great cleaner.
Problem is, if your purchasing aftermarket parts, your not going to afford he proper PPE.

But a properly labeled metal bucket with a lid in a yard with nothing within a 20ft radius, you could just put the parts in there to soak for a few days.




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[*] posted on 15-12-2024 at 03:33


If you have an ultrasonic bath, preferably heated, you can use a detergent solution or just boil them in a detergent solution. That's just for the metal parts and perhaps the O rings and the shaft seals. Probable not for the gaskets.

What I found was the above removed the oil sludge, leaving hard deposits next to the metal surfaces that has been below the sludge. Those hard deposits can be removed with stiff brushes and or plastic scoring pads.

Rinse with clean water and dry quickly, then coat with the vacuum oil you are going to use in the pump. Detergent washed steel parts rust quickly.

I noticed the service kit cost almost $500 Ouch !!!. I found that most of the O rings were standard sizes. Even the shaft seals. The only seal that defiantly needed replacing was the shaft seal between the motor and the outer housing of the pump. I replaced it with a double lipped seal. The original seal was single lipped, facing the oil. The doubled lipped seal will allow me to pull a vacuum on pump oil to decontaminate it of water and other volatiles.

The worn shaft seal can be caused by play in the shaft, though I failed to detect any play by hand.




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[*] posted on 21-12-2024 at 14:50


You might try using DCM to dissolve the polymerized oil, but that will wreck what is left of the gaskets. But they are likely toast anyway.
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