Fresh-Oil-Lubricated Rotary Vane Vacuum Pumps

Fresh-Oil-Lubricated Rotary Vane Vacuum Pumps 

Basically, multicell pumps are equipped with more vanes per impeller (commonly six vanes). The vanes of a multicell pump can only be moved by the centrifugal force and pressed against the inside wall of the pump chamber. 

When oil-lubricated rotary vane vacuum pumps are used in connection with a chemistry application, then usually fresh-oil-lubricated vacuum pumps will be chosen. The oil which in all rotary vane vacuum pumps serves the purpose of inner sealing and lubrication is constantly fed into the pump chamber and thus passes together with the gas, respectively vapour flow through the pump. 

The oil quantities within the pump chamber are relatively small, since the use of too much oil is prohibitive in view of the then occurring waste oil quantities. Because of the thus unavoidably restricted possibility of dissipating the compression heat, the active pumping section is cooled by means of a double water jacket. Fresh-oil-lubricated vacuum pumps which are intended for deployment in chemical production lines are manufactured with pumping speeds ranging from 50 to approximately 700 m h . The ultimate pressure attainable by these two-stage pumps reaches values down to 0.5 mbar (abs.) 

As in these vacuum pumps the oil passes only once through the pump, the purity of the separated oil is of far less significance compared to rotary vane pumps with circulatory lubrication. Even so, also in the case of fresh-oil-lubricated pumps, the aspect of vapour tolerance must be taken into account because here too the oil may suffer from dilution or the oil film in the pump chamber may be even washed away with the result of very rapid and considerable wear within the pump chamber giving rise to high repair costs. 

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Since in practice maintaining of these conditions was frequently found to be extremely difficult and since any early condensation within the rotary vane vacuum pump would result in considerable damage and thus high repair costs owing to the dilution of the oil, fresh-oil-lubricated rotary vane vacuum pump types were perfected for deployment in the chemical process industry. 

In this type of pump, the avoidance of condensation is no longer an absolute requirement as for oil-lubricated pumps with circulatory lubrication, even though it is still desirable to prevent any condensation also in fresh-oil-lubricated rotary vane vacuum pumps (risk of diluting the fresh oil too much). In any case, condensate which forms here can be discharged, since the exhaust of these pumps is not located at the highest point as is the case for types with circulatory lubrication, but instead the exhaust is located at the lowest point. 

Figure 5.9 Sectional drawing of a fresh-oil-lubricated rotary vane vacuum pump. (With permission from Dr.Ing-K. Busch GmbH, Maulburg, Germany.)...

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