Diffusion Pump operation

Just curious while working on a 4” wiped film or larger do I need to use liquid nitrogen when using a diffusion pump to pull deep vacuum or will dry ice be okay? Currently using e2m30.

Dry ice is fine, diffusion pumps are hard to break even if you do contaminate.


Would you recommend a bypass valve for backing? What vacuum level should I expect to see compared to just roughing pump?

You can do it through a path. The 6" that I learned on didn’t have one but I’m positive it will keep your diff pump oil cleaner by not pulling lights past it. If your normal pump is seeing 1.0e-1 to 1.0e-2 torr, a working diffusion pump should pull it into the 9.0e-3 to >1.0e-4 torr through the duration of the run.


It would depend heavily on how well you devol your feedstock. It’s probably worth it if you don’t devol in a reactor

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Once the diffusion oil soaks it no longer works. If you want to use diffusion you need to ensure your vapor pathway is dry and nothing is getting past your main hardware body. I secret with diffusion is using large pumps, high end oils, and super accurate gauges with immediate responce on screen. Also sweep tech helps with pulling all wet vapors out of system with a wet pump first.


Is that why people are using those high com boosters? If I’m deeper in vac should I turn my evaporator temp down?

What pumps are beeing used now ?
Oops yust saw your running a Edwards
How much distillate running per hour and what s your vacuum depth at now with the Edwards ?

The boosters are more for moving molecules down when doing dry work. The diffusion is another monster on its own. It doesn’t want a booster nc they the booster will splash the oil.

What vacuum level should I turn on at? Currently 400 micron not working.

Where are you reading you vacuum? 400 should be well low enough. What pump?

Edit: also what are you using to hit that pressure/is that all you’re able to pull roughing in? If so you may be leaking faster than the diff can pull

Reading just past the cold trap. I don’t think I have vac leaks using ax-65 diff on e2m28 under no load I’m pulling like 150 micron and it still doesn’t work.


When you say “sweep tech” are you referring to dosing the vacuum inlet with inert gas or using inert gas on the ballast?

Yeah manual says it should run fine anywhere below 500 mtorr. 150 mtorr with a dry still on an m28 sounds like a good bit of leakage or your pump needs attention

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During Distillation the sweep gas enters above the fluid on flask.

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I assume what he means because the clarification wasn’t quite clear is that when you rough down, there’s still atmosphere in the flask even when the pump stalls. In order to push that last bit of atmosphere which is frequently water vapor, you can intentionally leak a little dry gas directly into the boiling flask to push that water vapor out.

Did I get that right @spdking?


Is the heater working. On the diff ?
Those heaters go bust quiet often ?

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Yeah it’s hot, it just won’t pull vac.

What is your diffusion opperation process. Those pimps have a very exacting Sop to operate. What oil did you use. Dod you clean the inside of the pump with acetone and sterilize it (finger print oils can prevent diffusion from working right on startup) , and or did you assemble the diffusion pimp and run it under vacuum for 4-6 hours and watch the guage dip.

You need to tell us what you’ve done exactly. Diffusion is a analog style process. Only works one way. Of you didn’t install it right and or run it isolated to test it you won’t be able to run diffusion on your hardware. Also you should be using multiple pumps for scaling the vacuum range to diffusion.

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