When starting a centrifugal pump, should the pump or the valve be opened first?

The starting sequence and valve status of the water pump directly affect its safety and efficiency, and different pump types have different starting methods.

Centrifugal pumps must be started by "closing the valve and filling with water". Fill the liquid and exhaust before starting to avoid idling damage. Closing the outlet valve can reduce the motor load and current impact during startup (20%-30% of full load) to protect the motor. Open the valve slowly after starting to avoid overload or vibration caused by a sudden increase in flow. The principle is to close the valve to limit the flow, reduce the impeller resistance, and improve the mechanical efficiency by about 15%-20%.

Axial flow pumps are suitable for large flow and low head, and need to be started with a "fully open valve". The shaft power is extremely high at zero flow (up to 140%-200% of the rated value), and starting with a closed valve can easily burn the motor. Fully open the valve to reduce the pipe resistance, so that the pump runs at the maximum flow, the shaft power drops to 60%-80% of the rated value, and the starting current is significantly reduced (about 50% of the closed valve). If the valve is not fully opened, it may cause vibration or abnormal noise, and it needs to be shut down immediately. The principle is that the fluid impacts the blades evenly at high flow, with low mechanical loss and high efficiency (80%-90%).

The characteristics of the mixed flow pump are between those of the centrifugal pump and the axial flow pump. The zero flow shaft power is about 100%-130% of the rated value. It is recommended to start with a fully open valve to balance the load (starting current is about 70% of the rated value) and avoid the risk of impeller cavitation (cavitation margin>3m).

The vortex pump is suitable for high head and small flow. The zero flow shaft power is as high as 130%-190% of the rated value. It must be started with a fully open valve. Running with a closed valve for more than 30 seconds may cause the pump body to overheat and damage the seal.