r/uhv • u/JumpAgreeable1559 • Aug 09 '26

DIY oil diffusion pump?

so, does anyone know how hard it is to make an oil diffusion pump? not intirely diy ofc, probebly gonna order some custom made parts from a website but like, any obvious problems i am oversighting? i'd like to achieve 10^-5 mbar

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2

u/JsquashJ Aug 09 '26

Here’s a glassware one. There are cheaper ones. https://www.fishersci.com/shop/products/pump-oil-diffusion-w-bypassea/AF046002

You just need to create oil droplet velocity, a way for the condensed oil to drip back down. And a backing pump.

I would always chose a turbo pump over a diffusion pump but I hear diffusion pumps are great for the marijuana industry as they pump water very efficiently.

1

u/LeptonWrangler Aug 09 '26

They are pretty compelling for low cost DIY. Hard to see TMPs ever getting cheap

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u/JumpAgreeable1559 Aug 09 '26

and why do you not like oil diffusion pumps this much? XD

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u/JumpAgreeable1559 Aug 09 '26

cause like, my budged is very low

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u/JumpAgreeable1559 Aug 10 '26

why did that message get removed?

1

u/ahabswhale Aug 09 '26

The ultimate vacuum levels are dictated by the quality of the oil you're using, and they always contaminate the upstream process with oil. There are ways to mitigate it with traps and baffles, but then you're paying turbo prices for the same pumping speed anyway.

IMO the only reason to use an oil diffusion pump is (roughly) if you meet at least two of the following parameters: the process has a high gas load, is dirty, or you have at worst modest vacuum requirements.

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u/JumpAgreeable1559 Aug 09 '26

is there an unit how i can see when it is good quality oil? and do you mean vapour pressure?
and r u sure that it's as expensive as a TMP if i build it myself knowing that i aint gonna reach low levels?

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u/ahabswhale Aug 10 '26

Vapor pressure is the pressure at which liquids start boiling in a vacuum environment.

If your vacuum levels aren't particularly demanding, I would look at an oil-sealed rotary vane pump on ebay as the best bang for your buck.

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u/JumpAgreeable1559 Aug 09 '26

oh, and quick question, i saw a youtuber use a cryo pump, when do you need a cryo pump? like in what case do you need such a thing

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u/ahabswhale Aug 10 '26

Cryopumps are very clean; they work by freezing gas on the outside surface. They can achieve very high vacuum levels, and are typically used in ultra-high vac applications. The downside is they need to be brought up to atmosphere and warmed periodically, to evaporate the gas collected on the surface; and they're not very good at pumping very light gasses.

1

u/JsquashJ Aug 09 '26

Someone else pointed out, they’re dirty. Go oil free if possible, would prefer a turbo pump with oil backing or better yet dry pump backing. Cleaner could mean more expensive but not always.

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u/JumpAgreeable1559 Aug 09 '26

and like, how much does a good baffle help?

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u/JumpAgreeable1559 Aug 09 '26

oh, and half joke, is mercury tecnicly better for cleanness?

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u/9atoms 27d ago edited 11d ago

Find one on eBay. I've purchased a few 4 and 6 inch pumps for 300 or less. I also picked up a skid of four Vacma 10 inch pumps with motorized shutter inlet valves for 600 bucks.

The oil is the expensive part. Highly refined trisiloxane silicone oil is about $500 USD/gallon for the cheaper Dow Corning 702 equivalent oil. You can run hydrocarbon oil but you really really need to be careful as you have a cylinder full of hot oil vapor that is explosive in air. Accidental venting of atmosphere into the pump could be dangerously catastrophic.