Sciencemadness Discussion Board

Parting out rotovap from ebay questions

LD5050 - 28-3-2017 at 17:51

I was thinking of putting together a rotovap with different parts found on ebay. I was thinking of buying the main housing with the motor and everything that isn't working for around 200 dollars. I was wondering tho, why do these crap out typically? Is it usually just a wire issue or the motor just craps out? If its the wires that would be great if its the motor I'm sure you could just find a similar cheap electric motor and replace the old one?

Also the condensers, there is two different kinds I tend to see. The coil type and a "cold trap" type I guess you would call it. The cold trap kind I'm talking about has a removable concave glass piece that it seems you would maybe fill with dry ice?

Does the coil type condense low bp solvents under vacuum or would I need the cold trap type condenser? I don't know much about rotovaps so any info would be great.

organicchemist25 - 28-3-2017 at 20:47

I did the same thing, except I got everything from the university of Utah selling a whole setup, but non-working (eBay). It was a nice rig and paid a little more than 200$. My uncle works at a place that rebuilds electric motors. That's what was wrong with mine. It is a Buchi. In most instances, I'd say the motor fails.

If you can try looking for a whole unit that isn't working, if you have not already been doing so. Its either a rheostat or the motor. Its a very simple setup electronically. There could also bad seals. I also guess the heating element could be bad, but that would be pretty inexpensive.

All in all I got mine up and going for around 600$ for a complete original setup. It is 3500$ or more new.

Texium - 28-3-2017 at 21:44

Quote: Originally posted by LD5050  
Also the condensers, there is two different kinds I tend to see. The coil type and a "cold trap" type I guess you would call it. The cold trap kind I'm talking about has a removable concave glass piece that it seems you would maybe fill with dry ice?

Does the coil type condense low bp solvents under vacuum or would I need the cold trap type condenser? I don't know much about rotovaps so any info would be great.
I use a rotovap in the lab I work in all the time, and we actually use both types of condensers, with the dry ice/IPA filled Dewar condenser connected between the coil condenser and the pump. It depends on the solvent you're using. Normally for me it's either DCM or hexanes/ethyl acetate. With DCM, the dry ice filled Dewar condenser is definitely necessary. With hexanes/ethyl acetate, the water cooled coil condenser will catch the majority if the water flowing through it is ice cold, but if the rotovap is left on for a long time, it will evaporate again and be caught by the Dewar condenser. So if you don't want to fill your vacuum pump with solvent vapors, the Dewar condenser is kind of a necessity.

LD5050 - 29-3-2017 at 07:02

Any experience with the chinese models? There is a 2l rotovap for about 600 dollars brand new but made in china. I wonder how well these work/are made?