Why does the centrifugal pump start to close the outlet gate valve? Let us explain this reason today.
The centrifugal pump is generally driven by an electric motor, and the pump body and the suction line are filled with liquid before starting the pump. When the impeller rotates at a high speed, the impeller drives the liquid between the blades to rotate together. Due to the centrifugal force, the liquid is swept from the center of the impeller to the outer edge of the impeller (the flow rate can be increased to 15 to 25 m/s), and the kinetic energy is also increased. When the liquid enters the pump casing, the flow velocity in the volute casing gradually expands, the liquid flow rate gradually decreases, and a part of the kinetic energy is converted into static pressure energy, so that the liquid flows out along the discharge port with a higher pressure. At the same time, a certain vacuum is formed at the center of the impeller due to the liquid being pumped out, and the pressure Pa at the liquid level is higher than the center of the impeller. Therefore, the liquid in the suction line enters the pump under the pressure difference. The impeller rotates continuously, and the liquid is continuously sucked in and out. Since the centrifugal pump is capable of transporting liquid, mainly by the action of centrifugal force, it is called a centrifugal pump. So, what are the reasons for the centrifugal pump to start after closing the outlet valve?
Since the pump motor is in the starting phase, its rotor speed is from slow to fast, reaching the rated value, and its stator current is from large to small, reaching normal current. The starting current of the pump motor is generally up to 4 to 7 times the rated operating current value. In order to operate safely, it is necessary to try to start the motor under light load conditions, and then add the load to the rated value after entering normal operation. When the pump is started, the flow power is determined to be about 1/3, so that the maximum current can be avoided, so the centrifugal pump closes the valve to start. After the standby group speed is stable, open the valve, the opening time should be as short as possible, generally no more than 3 to 5 minutes, otherwise the friction inside the pump will cause damage to the pump parts.
