Laboratory managers specifying vacuum pumps have much to consider when evaluating the four basic types of pumps, and the tasks the pumps must perform.

Rotary-vane vacuum pumps reach deep ultimate vacuum levels and have high displacement capacity, making them a good choice for freeze-drying applications. Image source: Labconco.Labconco marketing content coordinator Allison Schach describes in a blog post how laboratories should go about selecting the right vacuum pump for the application at hand. Schach presents the features and benefits of four pump types—rotary vane, diaphragm, hybrid (combination of rotary vane and diaphragm) and scroll—and describes their use in typical lab applications, including freeze drying (lyophilization), evaporation and concentration.

(See the Engineering360 guide to vacuum pumps, their operation, specification, and product and supplier lists.)

Rotary-vane (RV) vacuum pumps, compared to other types, have a lower up-front cost, are smaller and can be used in multiple applications. They reach deep ultimate vacuum levels and have high displacement capacity, making them a good choice for freeze-drying applications. RV pumps work particularly well for aqueous samples and solvents with high boiling points, whose vapors can be easily trapped before they reach the pump.

Diaphragm vacuum pumps are dry pumps (no oil required) that use a pulsing motion that opens and closes valves to move air. The valves often are made of polytetrafluoroethylene, making the pump resistant to corrosives and less susceptible to damage from vapors. Therefore, almost any type of sample, even those containing a combination of solvents and acids, can be used with these pumps. This makes diaphragm pumps a good choice for evaporation and concentration. Diaphragm pumps cannot be used for freeze drying, since they lack sufficient depth of vacuum.

Combination or hybrid vacuum pumps use a diaphragm pump to keep the oil of an RV pump under negative pressure. This reduces or eliminates vapors going through it and condensing in the oil, keeping the oil cleaner and allowing for less-frequent changing; oil lasts up to 10 times longer.

Hybrid pumps are recommended for freeze drying corrosive or volatile samples--acidic samples and those containing harsh chemicals such as TFA, acetonitrile, HBe and nitric acid.

Finally, scroll vacuum pumps also are recommended for freeze drying, as they can be used with aqueous and solvent samples including acetonitrile. They also may be used with concentration applications.