[Babcock_Hall]

Is there a trick to improving water aspirator pump performance?  The best I have done recently in removing solvents such as water, toluene, and pyridine is a bath temperature of about 50-65 °C, which seems high.   I try to monitor the temperature of the water in the pump, and there is a slow flush of this water with tap water.  I also have a second water aspirator pump from a different manufacturer, but the last time I checked, its performance was worse than the first pump.

[discodermolide]

Is there a trick to improving water aspirator pump performance?  The best I have done recently in removing solvents such as water, toluene, and pyridine is a bath temperature of about 50-65 °C, which seems high.   I try to monitor the temperature of the water in the pump, and there is a slow flush of this water with tap water.  I also have a second water aspirator pump from a different manufacturer, but the last time I checked, its performance was worse than the first pump.

Well I would give it a clean out, perhaps the thing is gummed up! Change all the rubber tubing, check the seals on the rotavap. etc.
And I would use a vacuum regulator and run the aspirator with the tap turned on full.

[Babcock_Hall]

We just replaced the seal and the hoses last month, but I have not checked for clogs yet.

[discodermolide]

We just replaced the seal and the hoses last month, but I have not checked for clogs yet.

If that doesn't work attach a membrane pump to the rotavap.

[orgopete]

I don't know whether this is poor performance or not. I always had a vacuum gauge on my rotovap. The other side of this is expectations. You could calculate the amount of heat required to evaporate your solvents. If you want to evaporate it faster, use a higher bath temperature to overcome the low heat transfer of glass. The bath temperature is not the vapor temperature either. Just drop the bath, wait a few seconds, and feel the flask, is it hot? I'm guessing it is not.

In doing any distillation, I found the bath temperature was often around 15-20°C above the boiling point, depending on the boiling point.

[Wastrel]

Aspirators vary, some are better for volume some for ultimate pressure.  Water pressure in our labs, and hence ultimate vacuum, used to vary according to how much was being used at any one time.  We didn't have non return valves and I'd have liked the safety net, do they reduce ultimate pressure?

Something I didn't get to try with a rotavap, but works well with regular vacuum distillation, pump down, seal off and cool the receiving flask.

[AlphaScent]

Have you thought about making your own aspirator pump?  With this you can control the temperature of the water and you do not waste water down the drain; you reuse it in a cyclic fashion.  If interested, I can elaborate. 

[milo2112]

I have found the cheap ones from VWR or Fischer are the best. I think they come in packs of 20. It is important, especially for metal aspirators to clean them out once in a while. Also, using cold water tend to get you better vacuum. As far as bath temperatures goes, I routinely use a bath of 80C. Water, glycol, pyridine, NMP etc all come off at that temp and aspirator pressures (although the NMP tends to take a while). As long as you are using DI water (i.e. no salts), there is no reason your bath cannot be at close to boiling.

[Babcock_Hall]

Have you thought about making your own aspirator pump?  With this you can control the temperature of the water and you do not waste water down the drain; you reuse it in a cyclic fashion.  If interested, I can elaborate. 

This sounds interesting.  We circulate our cooling water for similar reasons.

[Babcock_Hall]

As far as bath temperatures goes, I routinely use a bath of 80C. Water, glycol, pyridine, NMP etc all come off at that temp and aspirator pressures (although the NMP tends to take a while). As long as you are using DI water (i.e. no salts), there is no reason your bath cannot be at close to boiling.

I have a BOC group on the product of interest, and I am a little bit worried about decomposition at higher temperatures.