Rotary Plunger Vacuum Pump

As for the rotary vane vacuum pump, condensation of pumped solvents in the vacuum pump resulting in a dilution of the lubricating oil can only be accepted to a very limited extent, preferably not at all. 

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Grculatory-ljubricated Rotary Vane and Rotary Plunger Vacuum Pumps... 

If this is not accomplished, condensation occurs in oil-sealed rotary vane or rotary plunger vacuum pumps, resulting in a severely impaired ultimate pressure and pumping speed and, moreover, these vacuum pumps may suffer significant damage. 

Fig. 6.2. Internal-vane, external-vane, and plunger-type rotary vacuum pumps. It will be noted that the internal-vane pump involves a rotor concentric with the drive shaft, but which is off-center with respect to the stator. By contrast, the external-vane and rotary-plunger pumps have a rotor which is asymmetric with respect to the shaft however, the shaft is centered in the stator. All three involve close tolerances, so the high-vacuum performance is impaired by particles of dirt or corrosive gases. Some pumps are partially constructed from soft die-cast metal, which is eroded by mercury. Special corrosion-resistant pumps and inert flourinated pumps are used in the semiconductor industry.

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