US Patent 7114889 Powdery particle conveying system and roots blower operating method

A powdery particle conveying system is provided in which electric power consumption can be saved when powdery particles are conveyed by use of a roots blower. In the case where the powdery particles are conveyed to a reservoir tank near the roots blower, the frequency of a power source of a roots blower driving motor is reduced, thereby reducing an output of the roots blower. In contrast, in the case where the powdery particles are conveyed to a remote reservoir tank, a voltage of a commercial frequency is applied to the motor.