Looking at vaccum pumps

Ground Up Think Tank
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Hey guys, i was wondering what u all thought of this vaccum pump?

https://www.amazon.com/dp/B07WS97JWQ/ref=cm_sw_r_cp_apa_glt_fabc_ADNJF2QPRFC4VX8VB4ZN

I was gunna try it on a 2l roto and see if it would go good for a spd… i doubt it will

I was also looking at a wobl but i was worried it would be too much for my little roto lol ty

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Start here with a decent comparison chart of vacuum levels.

This pump has a stated spec of “-85 KPa”. Looking at the handy chart, you will notice that the “-” is not correct notation which should be a red flag right off the bat. Let’s go ahead and pretend that maybe they just have a shitty marketing department. 85KPa is nominal vacuum. A two year old could produce this vacuum level in a sippy cup.

For rotary evaporation you need around 40-50 Torr.

Moving forward, it is easy to check these things yourself if you are armed with the specs you need and know where to look. Your primary concerns are:

  1. Pump Size (volume) : this is the amount of gas it can move in a given time period. You will see this expressed in terms of volume/time like 3L/min
  2. Ultimate vacuum: (base pressure): this will be expressed in terms on the handy vac chart- Torr, Inches of Hg, Kilo-pascals KPA etc

Looking at the chart, you can see that some measurements are far more granular and expressive than others. For example, Inches Hg and Torr. Follow the chart from 28’ to ultimate vacuum and see what the Torr scale is like. the difference between 29.53 and 29.96 s the difference between passing a residual solvent test and not.

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For a 2L Roto, you’ll want a diaphragm pump that can reach your desired ultimate vacuum pressure. I know you’re probably not worried about solvent recovery efficiency, but use this link from one of my distributors as a general guide to understanding the process and dialing in parameters.
https://rotovaps.net/blogs/blog/putting-the-rule-of-20-into-practice

If you’re working with ethanol, you’ll want a pump that can reach at least 100-150mbar… but you’ll probably want something a stronger like @Sidco_Cat mentioned. I’d say your sweet spot for ultimate vac is anywhere in the 15-50Torr/mbar range. This of course depends on your coolant temp and your bath temp as well. Pumping speed is not a priority (compared to SPD) when it comes to a small 2L roto, but you’ll want something with at least 10~15 Liters per minute.

I’ll let the SPD folks give their input and recommendations… the pump you linked isn’t going to cut it for that.

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