Sciencemadness Discussion Board

Diffusion pump oil

ElizabethGreene - 6-2-2017 at 12:29

Are there any common chemicals that can be used as a diffusion pump oil?

I'm hesitant to put $100 of oil in a pump I built for $20.

Thanks.

unionised - 6-2-2017 at 13:21

Interesting question.
What sort of oil did you build it to use?
Some of the hydrocarbon oils are a lot cheaper than the silicone ones. (Don't look at perfluorocarbon oils the prices will stop you sleeping at night)

ElizabethGreene - 6-2-2017 at 15:14

Sadly, in my haste to make something, I neglected to find out. :/

Source:
http://www.belljar.net/fbleediffpumps.pdf

Another sketch from the same source (http://www.belljar.net/hickman.pdf) mentions Butyl Phthalate and I _assume_ that these are designed for the same.

That same oil was mentioned here (fascinating book, btw) https://archive.org/details/ProceduresInExperimentalPhysics .

I made stupid rookie mistakes in assuming a. the oil in diffusion pumps was all interchangeable and b. not price checking it..

Heavy Walter - 7-2-2017 at 04:47

Hi
At my very begginings in the high vacuum art & science, I used succesfully Butyl Phthalate.
25 years later, only Polyphenyl Ether. Cleaner vacuum, higher resistance to harsh conditions (sudden involuntary air admission, reactive/corrosive gases).

DJF90 - 7-2-2017 at 05:15

Quote: Originally posted by ElizabethGreene  
That same oil was mentioned here (fascinating book, btw) https://archive.org/details/ProceduresInExperimentalPhysics .

I made stupid rookie mistakes in assuming a. the oil in diffusion pumps was all interchangeable and b. not price checking it..


Thanks for bringing that book to my attention; it looks really useful and interesting so I've just ordered a used copy from Amazon.

As for working fluids, mercury used to be used quite commonly, but a pump designed for mercury is not suitable to use with oil (and vice versa). Common working fluid for oil diffusion pumps is dibutyl phthalate, and also dioctyl phthalate (octyl in this case is not n-octyl, but 2-ethylhexyl) can be used.

ElizabethGreene - 14-2-2017 at 13:34

Follow-up on this.

I found a DIY diffusion pump instructable, and that chap used the non-volatile component of 3-in-1 Silicone Spray Lubricant for oil. According to the MSDS, it's 95-99% volatile hydrocarbons and 1-5% Poly-(dimethylsiloxane).

I _almost_ tried this, but decided to order proper oil instead of vacuum distilling off several cups of flammable mystery hydrocarbons through my shiny new vacuum pump.

I ordered from http://diffusionpumpoil.com, and will post results when I test it. Now I have to get a better vacuum gauge.