1. Fill the pump casing with water to form a vacuum.

2. The gate valve on the outlet pipe must be closed so that the pump does not form a flow, which can reduce the motor starting current and facilitate the smooth start of the pump. The gate valve should be opened slowly and in time as the pump starts smoothly. The centrifugal pump relies on the centrifugal force of the impeller to form a vacuum suction to lift the water. Therefore, when starting the centrifugal pump, the outlet valve must be closed first and water must be filled. The water level must exceed the impeller part, and the air in the centrifugal pump must be discharged before it can be started. After starting, a vacuum is formed around the impeller, sucking the water upward, and it can automatically open to lift the water. Therefore, the outlet valve must be closed first.

 

③ Generally, there is no self-priming ability, and the pump needs to be filled with liquid or the pipeline needs to be evacuated before it can start working.

 

 

Centrifugal pumps are generally driven by electric motors. Before starting the pump, the pump body and the suction pipe are filled with liquid. When the impeller rotates at high speed, the impeller drives the liquid between the blades to rotate together. Due to the centrifugal force, the liquid is thrown from the center of the impeller to the outer edge of the impeller (the flow rate can be increased to 15-25m/s), and the kinetic energy increases accordingly. After the liquid enters the pump casing, the flow channel in the volute-shaped pump casing gradually expands, the liquid flow rate gradually decreases, and part of the kinetic energy is converted into static pressure energy, so the liquid flows out along the discharge port at a higher pressure. At the same time, a certain vacuum is formed at the center of the impeller due to the liquid being thrown out, and the pressure Pa at the liquid surface is higher than that at the center of the impeller. Therefore, the liquid in the suction pipe enters the pump under the action of the pressure difference. The impeller keeps rotating, and the liquid is continuously sucked in and pressed out. Since the centrifugal pump can transport liquid mainly by the action of centrifugal force, it is called a centrifugal pump.

 

Start-up of other centrifugal pumps

1. Large flow starting characteristics of axial flow pumps - fully open valve starting. The shaft power of axial flow pumps is maximum at zero flow conditions, which is 140%~200% of the rated shaft power. The power is minimum at maximum flow. Therefore, in order to minimize the starting current, the starting characteristic of the shaft power should be large flow starting (i.e. fully open valve starting).

2. Starting characteristics of mixed flow pumps - fully open valve starting. The shaft power of the mixed flow pump at zero flow conditions is between the above two pumps, which is 100%~130% of the rated power. Therefore, the starting characteristics of the mixed flow pump should also be between the above two pumps, and it is best to start with a fully open valve.

3. Starting characteristics of vortex pumps - fully open valve starting. The shaft power of the vortex pump is the largest under zero flow conditions, which is 130%~190% of the rated shaft power. Therefore, similar to axial flow pumps, the starting characteristics of vortex pumps should be large flow starting (i.e. fully open valve starting).