If the centrifugal pump uses three-phase power source, it doesn’t need any capacitor. In case of single phase power source, the capacitor of the pump’s motor is used to change the phase angle between motor starting winding and motor operating winding. In other words, the capacitor will produce rotary magnetic field. Normally, the difference among the three phases is 120 degrees, single phase 180 degrees. The forces will be balanced and the motor will not run. That problem is solved by adding a capacitor.