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When the multistage centrifugal pump is started, the outlet valve must be closed

2020-08-25

When the multi-stage centrifugal pump is started, there is still no water in the outlet pipe of the pump, so there is no pipeline resistance and lifting height resistance. After the multi-stage centrifugal pump is started, the head is very low and the flow is large. At this time, the pump motor (Shaft power) The output is very large (according to the pump performance curve), and it is easy to overload, which will damage the pump motor and circuit. Therefore, the outlet valve must be closed when starting to make the pump run normally.
 
Before starting the multistage centrifugal pump, two points must be guaranteed:
 
1. Fill the pump casing with water in order to form a vacuum;
 
2. The gate valve on the outlet pipe must be closed, so that the water 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 in time as the pump starts smoothly.
 
The multi-stage centrifugal pump lifts the water by the suction of the vacuum formed by the centrifugal force of the impeller. Therefore, when the centrifugal pump is started, the outlet valve must be closed and water is filled. The water level is above the impeller, and the air in the multi-stage centrifugal pump can be started. After starting, a vacuum is formed around the impeller to suck up the water, and it can be automatically opened to lift the water. Therefore, the outlet valve must be closed first.
 
About multistage centrifugal pumps
 
Multi-stage centrifugal pump is a kind of vane pump, relying on the rotating impeller in the process of rotation, due to the interaction between the vane and the liquid, the vane transfers mechanical energy to the liquid, so that the pressure energy of the liquid can be increased to achieve the purpose of transporting the liquid.
 
The multi-stage centrifugal pump has the following characteristics:
 
①There is a limit value for the head produced by the multistage centrifugal pump at a certain speed. The operating point flow and shaft power depend on the conditions of the device system connected to the pump (position difference, pressure difference and pipeline loss). The head changes with the flow.
 
② Stable work, continuous delivery, no pulsation of flow and pressure.
 
③Generally, there is no self-priming ability. It is necessary to fill the pump with liquid or vacuum the pipeline before it can start working.
 
④The multistage centrifugal pump is started when the discharge pipe valve is closed, and the vortex pump and axial flow pump are started when the valve is fully opened to reduce the starting power
 
Before the pump is started, the pump casing is filled with the liquid being transported; after starting, the impeller is driven by the shaft to rotate at a high speed, and the liquid between the blades must also rotate with it. Under the action of centrifugal force, the liquid is thrown from the center of the impeller to the outer edge and gains energy, leaving the outer edge of the impeller at a high speed into the volute pump casing.
 
In the volute, the liquid decelerates due to the gradual expansion of the flow channel, and part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipe at a higher pressure and is sent to the place where it is needed. When the liquid flows from the center of the impeller to the outer edge, a certain vacuum is formed in the center of the impeller. Because the pressure above the liquid level of the storage tank is greater than the pressure at the inlet of the pump, the liquid is continuously pressed into the impeller. It can be seen that as long as the impeller rotates continuously, the liquid will be continuously sucked and discharged.
   

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