Rotary evaporators are among the most common applications for vacuum in chemistry labs. Yet how many people give a lot of thought to the pump used to provide the vacuum? Here are a few tips.

Decide first how much vacuum you need. Any solvent but DMSO can be brought to boiling at room temperature with a diaphragm pump, so the first step is to avoid using oil-sealed pumps whenever possible. The excess vacuum makes your evaporations too difficult to control, and you incur needless maintenance demands.

Next, avoid oversizing the pump. Remember, when the condenser on your evaporator is 20 degrees Celsius cooler than your sample, it will condense most of the vapors leaving the evaporator. That means that a small pump with modest pumping capacity – 1 cfm or less – will provide enough pumping to manage the residual vapors that reach the pump from most benchtop evaporators.

“Think about vacuum, pumping speed, controls and vapor capture.”

Then, consider vacuum control. Too much vacuum can cause foaming and bumping, and too little vacuum will slow your evaporations. A pump with electronic vacuum control will ensure that you optimize your evaporations for both speed and sample protection.

Finally, think about vapor capture. The vapors coming off the evaporation can condense in the vacuum lines as they cool. An inlet separator protects the pump from condensed liquids. A catchpot on the outlet will collect exhausted vapors that condense as the vacuum is released. Add an exhaust condenser to your pump, and you can bring vapor capture to 98 percent or more – and avoid discharging those vapors through your fume hood to the atmosphere.

For help selecting a pump for your rotary evaporator, try VACUUBRAND’s Vacuum Pump Selection Guide. Just answer a few simple questions about your process, and get a recommendation for the best pump for the job.

At VACUUBRAND®, we are experts in vacuum for science. To learn more about our laboratory and OEM vacuum pumps, please visit our website. If you’d like details about our modular, energy-saving alternative to central vacuum systems for labs, our technology microsite offers an overview. Or simply contact us today about your lab vacuum needs.