Centrifugal pump start reason after close the outlet valve
|Centrifugal pump driven by a motor in general, before starting the pump, the pump and the suction pipe is filled with liquid. When the impeller rotates at high speed between the blades of the impeller to drive the liquid along the rotation, due to the centrifugal force, the liquid thrown to the outer edge of the impeller (flow rate may be increased to 15 ~ 25m / s) from the center of the impeller, the kinetic energy increases. When the liquid enters the pump housing, since the pump casing volute gradually expanded in the flow path, the liquid flow rate decreases, a part of the kinetic energy into static pressure energy, so a high pressure liquid flows along the discharge outlet. At the same time, the impeller due to the liquid was thrown at the center and create a vacuum, and the pressure Pa at the level higher than that at the center of the impeller, and therefore, the liquid in the suction pipe into the pump differential pressure. Constantly rotating impeller, the liquid is sucked and continuously pressed out.
Since the motor at start-up phase, the rotor speed from slow to fast, to rating, its stator current was descending to reach the normal current. Motor starting current is generally up to 4-7 times the rated current value. For safe operation must try to make the motor start under light load conditions, to be entering the normal operation after the load is applied to the nominal value. When the pump starts to flow power determined to be about 1/3, so you can avoid the maximum current, the centrifugal pumps are off valve start. Standby group after speed and stability, open the valve open time should be as short as possible, generally no more than 3 to 5min, otherwise the pump will cause friction heat pump parts damage.