Question good vacuum pump for short path distillation and rotovap

[mycelium]

What is the best pump to buy, to be used both for a short path distillation set up, and for a roto...probably even filtration. I don't want to spend 2 grand on the pump, but it has to do the job, and do it right...
I know some syntheses say to use reduced pressure, but some say to distill under 40mm Hg which is close to a full vacuum and probably not going to happen with a 100$ HVAC pump.
One that comes with a roto , in this picture, uses water in the bottom of the pump to make a vacuum...do you think it will get down to 40mm Hg?
Thank you

 

[mycelium]

Don't want this post to disappear.
Can you tell me what this kind of pump is called, with water down below
And won't cold water make it more vac, in which case it wouldn't do a real vac all the time...
I am going to look at the vacuum guys post...

 

[ruen]

have you heard of chatgpt? its this new cool ai thing kids are using to pretend they are smart

To compare 1.33 mbar and 40 mmHg, we need to convert them to the same unit. Let's convert 40 mmHg to mbar:

Conversion factors:​

• 1 mmHg ≈ 1.33322 mbar

So:
40 mmHg × 1.33322 mbar/mmHg ≈ 53.33 mbar
Now compare:

• 1.33 mbar vs 53.33 mbar

Interpretation:​

• Lower pressure means a better (stronger) vacuum.
• 1.33 mbar is much lower than 53.33 mbar, so:

1.33 mbar is a stronger (better) vacuum than 40 mmHg.

No, 40 mm Hg is not close to a full vacuum.
Here’s why:

• Atmospheric pressure at sea level is about 760 mm Hg.
• A perfect vacuum is defined as 0 mm Hg (complete absence of pressure).
• So 40 mm Hg still represents a significant amount of pressure—about 5.3% of atmospheric pressure remains.

In vacuum terms:

• 40 mm Hg absolute pressure = 720 mm Hg vacuum (since vacuum is often measured relative to atmospheric pressure).
• That would be called a partial vacuum, but not a "high vacuum".
• High vacuum typically starts below 1×10⁻³ mm Hg (or 0.001 mm Hg), and ultra-high vacuum is much lower.

Conclusion:
40 mm Hg is a moderate vacuum—not close to a full (or perfect) vacuum.

check this post to learn more https://bbgate.com/en/threads/providing-and-application-of-vacuum-in-a-laboratory.813/
nevertheless, apparently a simple water aspirator can reach 32 mbar. you could also use that circulating water to cool your condenser. and it is propably cheaper as well. my suggestion would be to get one of those instead.

 

[Osmosis Vanderwaal]

1.33322mnbar represents the rotary evaporator above this contraption, this vacuum pump/condensor pump says 0.098 m pa

 

[Osmosis Vanderwaal]

Is there something that says the vacuum pumps use the water? I thought there was a vacuum pump and a water pump for the condensor that were not the same apparatus, but it doesnt make clear what kinbd of pump it uses. If it can pull 0.098mbar, that boils water at 7c 44f so you thats pretty good vacuum. about 7350 microns

 

[Osmosis Vanderwaal]

It actually DOES pump them both from the same pump. It's a liquid ring vacuum pump and they work similar to a rotary vein pump, but the outside of the impellors move water so the air pressure is sealed but theres no friction. it has an offset shaft and the pricipal is similar to a rotary vein

 

[Osmosis Vanderwaal]

yes, it can get quit a bit lower than 40mm/hg, down to about 8-9mm/hg is the claim. Yes the water temperature affects it, so get that $99 mini ice machine too ( I have one)

 

[mycelium]

Well, a chiller comes w the roto, down to -5, but I can make a cooling bath to a lot lower if necc

 

[Osmosis Vanderwaal]

the last couple of vacuum pumps that I've bought I've stared at this unit for a week before I bought something way cheaper. I never really looked hard at how this thing worked, but now that I have, it's a lot more awesome than I thought. In the realm of vacuum, I don't think it's considered high vacuum, or maybe just barely, but in the realm of what we usually do, it's got some pretty great vacuum. Before I start a distillation I start filling up the bins with ice and put a 6 pack of water in the freezer too, then I just drop them in the bucket where resides my recieving flask and my aquarium pump and I perioducally scoop out some water and replace it with Ice and use the bottles in between. Even if a set-up isn't relying on the vapor pressure of water (ie the temperature of the water), you can distill faster with colder water because it condenses the liquid faster. Eventually, if you try to go faster faster faster, the gas escapes out of the far end of the condensor, or it's sucked into your vacuum pump because it didn't cool enough to condense. I've spent 1000 hours staring at a distillation rig or staring into a pyrex pie plate, waiting on crystals to form, or fiddling with that crap.
Some people might not know; if you take a piece of vacuum line and stick the end in your ear, you can go around your joints with the other end and hear air leaks easily. Sort of like a stethoscope