I’ve only used turbo pumps personally and I find the leybold turbovacs to be sufficient enough for distillation down to 0.4mTorr when there’s relatively little volitals in the system. I’ve noticed a lot of folks like to run diffusion pumps, and looking at some on eBay I’m considering one.
Anyone with more experience with these pumps would be beneficial to discuss their experience.
The biggest issue with diffusion pumps is that they can backstream, the value in them is there is basically no maintenance and can take whatever damage you want to throw at it. You’ll need to watch out on the type because they often contain mercury to move the molecules through them… which you could imagine how bad it would be to backstream mercury into your material. Turbo’s require a much cleaner environment and can be catastrophically damaged by particles in the vacuum. There is a massive amount of kinetic energy in them operating 30-90k RPM so particles hitting blades at that speed can cause it to self destruct. The value is that there is nothing to backstream so they are extremely clean, but any maintenance is a costly one.
The guys at fusor.net have a lot of great vacuum information, particularly the faq in the vacuum sub Vacuum Technology (& FAQs) - Fusor Forums However they are very picky about requiring use of real names when posting on their forum.
With a turbo I would expect to get much lower than .04 mTorr, my rotary vane Edwards e2m28 goes to .75 mTorr, but my Varian Turbo V-301 goes to 3.7e-7 (.00000037) mTorr
Diff pumps today dont contain murcury (unless you get an antique off ebay), there are a few different types of fluids one could use (maybe discuss in its own topic cause they all aint anything i would eat) You are correct in that they can backstream, especially in the ranges we use them (not if you startup/shut down correctly, and have vacuum lines designed to condense any backstreaming particles)
I hear of some folks using the Turbos on their wiped films, and it makes me cringe. Those high rpm’s a turbo requires wont last if a single drop of entrained material (terps) enters inside it.(I can immagine it woudl be pretty violent situation) Im sure folks are running them with little issues, and would think such system would greatly benefit from a N2 blanket/purge/sweep. Knowing that Chemtech is providing lybolds, I cant help but to wonder if turbos may be a bit more resillient to our process than I have thought. But my gut tells me it would need be a perfect situtation every day to ensure a turbo’s successs. Maybe with 2 traps and entrainment separator I could use a turbo with confidence.
I want to add Vapor Booster pump to this discussion.I have not tried one on cannabis wiped film yet, but waiting for the right opourtunity. They are not dry pumps, and closer to diffusion pumps than turbos.
I have run a turbo on a WFE successfully before, with only one incident in 1.7 years with terpene fouling, the key is to have your traps as effective as possible. The leybold turbos are pretty resilient, but how you orient them and set up your vac line can determine success. Putting a manual valve between the trap and the roughing pump/turbo and pulling vac on the rest of the system with an auxiliary roughing pump when changing collection vessels and such is key. The turbos do not like to have a sudden pressure spike if you introduce positive too quickly (such as pumping a new collection flask down from 1 ATM to mTorr)
That doesn’t mean I’m utilizing it correctly, always looking to improve that WFE rig.
Not to mention there’s not too many places in North America that can ballance the turbo pumps rotor. Maintenence and absolutely no room for error are the two biggest issues with the turbo pump. The possibility of oil back streaming into the foreline is the only drawback to the diffusion pump in my opinion. A good cold cap will mitigate that .
It seems like so far the opinion is leaning towards modern diffusion pumps?
Based off what @drPaul said perhaps turbo pumps have also made enough advancements that the risk of a long lead time on fixing a turbo might be worth the risk of operating one.
Modern turbopumps are nice, if you choose that route I would definatly have a a spare in Stock.
Here is a nice pic I found of some poor lads pump that ate itself.
@Soxhlet, how exactly does one do that to their turbo? Poorly balanced?
We learned the hard way about spare turbos the one time ours did get fouled up. It was a solid 2 weeks of running just roughing pumps. Thank God for decent pumps though.
My take on turbos: Turbo pumps are excellent for DRY systems, where you need consistent low pressures, but are definitely NOT introducing liquids (think: particle accelerators, mass spectrometers, etc.); many turbo pumps are sensitive to contamination and pressure pulses, either of which can trigger a controller shutdown. Depending on the controller type, the pump may have to spin down quite a bit before it can be restarted, all of which would cause significant grief in the middle of a distillation!
On top of that, rebuilds are costly, and definitely NOT in the field-service category. Keep in mind that the larger pumps spin in the thousands of rpm, and some of the smaller units rev up to 30,000 rpm or higher. I’ve seen turbos that ‘blew’ where all that was left of the previously beautiful vanes were what looked like steel wool (significantly worse than Soxhlet’s photo…like, nothing resembling vanes left, at all!). Not suitable for the kind of applications we’re discussing!
Diffusion pumps, on the other hand, have no moving parts, can tolerate a good deal of junk flying around (terpenes? loose crud?), and are easy to service…pour out the used oil, clean with acetone and a little steel wool on carbonized deposits, and you’re good to go. Cheaper, too. While turbos, even on the eBay market, may start out at a few hundred dollars, keep in mind that they need to be mated with a specific controller, and the latter are often not part of the eBay offerings. It can get pricey.
I didn’t read any of this thread and I know this is the right answer. We run several difftaks and they are the bees knees. All bought used, they’re rugged AF
Roots style vacuum pumps are the shit but they don’t go quite deep enough for most of our applications. They run about a decade higher than rotary vane pumps. That being said, they are the shit for backing pumps. We run out entire lab including a few diffusion pumps off one ADS602LM. Bought used for $3k it’s not a cheap pump but for what we get out of it there’s no alternative
Blowers can only be used if they have magnet decouplers built in or else they can over pressure a backing pump. They are used in distilling when there is excess pressure from degassing at rapid rates. And as a third stage sometimes. They are perticular for large pumps where the curve dives off at low micron.
