Rotary vs centrifugal vs diaphragm pump


#1

Hello I’m in the market for pumps for my rotovap and distillation machine I just wanted to know what are the benefits to a rotary vane pump compared to a centrifugal pump. And whats the benefits of a diaphragm pump?


#2

Rotery pump will exceed the vacuum level needed for a rotery evaporator, it will require a cold trap and a vacuum controller. Not to mention frequant oil changes.

A diaphragm pump will provide the best option,for your rotovap. It wont overpower the whole show, and wont suffer from oil contamination.

Are you talking about a blower here or a water pump? Mabey reffering to a scroll type pump?


#3

I mean a sliding vane pump I apologize


#4

Also, what kind of pump do you recommend for my short path system? A diaphragm pump as well?


#5

Basically 3 different pumps you’ll use for the roto. There’s lots more but I’ll stick to the main 3 here. (listed in order of vacuum depth)

  1. diaphragm pump- these are the most common for style pump for use with the rotovap. They do not use any oil and are fairly chemical resistant. This makes it perfect for recovering fairly volatile solvents like alcohol, pentane, etc. If the pump ingests any solvent it simply spits it out of the exhaust. These are usually limited to lower vacuum levels. To reach medium vacuum depths (single digit Torr) they require multiple heads connected together and this increases the cost substantially.

  2. Dry scroll pumps-These pumps can operate at deeper vacuum levels and are also chemical resistant as they also do not use oil. Dry scroll pumps can be more expensive upfront but have the largest overall operating range. They can go down to ~50mTorr so they can even be used as a backing pump. They are usually used for operations which might require fairly deep vacuum, but they can be used for anything in between. Really nice to have around when you need to distill some higher boiling point materials.

  3. Rotary Vane Pumps- These pumps use sliding vanes and oil to achieve much deeper vacuum levels and are the most common, but are generally not used with a rotovap. They cannot operate for long periods at lower vacuum levels common with a rotovap. They can be used for things like freeze dryers and even distilling high boiling point materials in the roto like polymers and what not, but they must be operate at deep levels otherwise they tend to overheat. They also ingest anything from your vacuum stream so you’ll need to use cold traps. These style pumps are most commonly used with the short path distillation systems as either the main pump or a backing pump. They can typically reach vacuum levels of less than 1 mTorr when new or rebuilt.


#6

stick to a rotery vane for spd, deeper vacuum levels.


#7

Yeah but to maintain a longer lasting life to any of the 3, it’s smart to use a cold trap between them all for a rotovap extraction. Personally I use a cold trap between my diaphragm vacuum pump and rotovap because I spent almost 500$ on the thing and I don’t wanna have to replace anything for a long time. *Reducing corrosive chemical intake to any vacuum pump is probably one of the best ways to keep it alive longer.


#8

I’m not going to disagree. Frankly cold traps are always a benefit and terpenes will destroy any pump.
I would only add that a cold trap is simply a condenser, and with a rotovap you already have an oversized condenser so you just have to make sure not to overwhelm it. If stuff is condensing on the top 1/4 of the condenser you’re probably going too fast. I use a diaphragm pump without a trap while recovering the bulk of ethanol, but any other pump needs a trap.


#9

I use a diaphragm pump that is rated chemical duty for running DCVC and filtration via Buchner funnel. No other style is suitable. I do not run a cold trap in any scenario.

I use a dual vane pump for creating the vacuum needed for mean free path (MFP) flow conditions inside a distillation apparatus. For me I set the target no higher than 15 microns but typically can pull down to one micron during MFP operation of my sublimation apparatus. I remove the bulk of the lower boiling compounds than THC via a liquid to liquid extraction so am not ingesting much terpene but a little does foul the oil. This is easy to remedy by swinging the pressure from time to time and allowing fresh air to flush down through the system but avoiding the distillation process by valve placement. Ingesting terpenes does not harm this pump but will in time damage the oil to the point an oil change is needed. A simple operation.

It takes two pumps when coping with heavy fume first and requiring MFP conditions as well. The two do not cross over. I chose a dual vane pump for MFP operations because they are built like tanks and by design sacrifice the consumable pump oil first before the pump itself croaks. They cannot tolerate very much organic solvent fume though before failure and are simply the wrong tool for operations regarding fume. A diaphragm pump could never reach MFP conditions in a distillation rig but if outfitted as chemical duty as mine is they are rated to tolerate organic solvent fume all day long. The internal wetted path is all PTFE (teflon) and seems to tolerate even the inevitable hexane or ethyl acetate fume produced from DCVC. A dual vane pump would fail quickly after ingesting hexane and ethyl acetate fume, so each pump has a niche.

The higher end pumps get more esoteric and also tend to have power requirements and noise considerations beyond what I would ever set up for given my location at home.:nerd_face:


#10

I have this https://www.newstarenvironmental.com/rocker-300c-ptfe-coated-chemical-resistant-vacuum-pump.html but I still prefer to use a cold trap.


#11

I agree here - diaphragm pump is great for not only rotary evaporators but using with a Büchner funnel (or also if you’re just doing simple distillation with basic glassware)

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