When to start the pump with discharge valve open ?
1. Usually we need to start the pump with discharge valve closed. because if we start the pump at rundown point, power requirement is very high. And possibility of tripping of pump or burning of motor. Where specific speed is less than 2000.
2. If the specific speed of the pump is above 6000 then power requirement is high at the shut off head or at zero flow and power requirement is less at rundown point.
3. That’s why we need to start the pump with discharge valve open is such a case. Where we have axial flow area.
4. lower specific speeds produce flatter curves, while higher specific speeds produce steeper ones. And It should be noted that the efficiency and power consumption were calculated at the BEP.