Power Requirement of a Roots Vacuum Pump

As already discussed, compression within a Roots vacuum pump being an outer compression is isochoric. 

In addition, also the mechanical power loss Ny of the machine needs to be provided  

As to the work on compression which needs to be provided, the following approximation applies  

Thus the rating for the drive motor for a given size of Roots vacuum pump depends on the permissible maximum pressure difference and the amount of mechanical power loss depending on the design in which also the amount of power required for starting up the pump must be taken into account. 

Examples for the power uptake of Roots vacuum pumps, dependent on the pressure difference, are given in Table 5.2 for a pump with a theoretical pumping speed of 1000 m h  

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Table 5.2 Power requirement of a Roots vacuum pump as a function of the pressure difference.

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