Centrifugal pump this grinding leprechaun, at the start, need to pay attention to a lot of matters, do not close the outlet valve when the centrifugal pump starts? Shock! The answer turned out to be...
1
Why do you have to close the outlet valve when starting the centrifugal pump?
When the centrifugal pump starts, there is no water in the outlet pipe of the pump, so there is no pipeline resistance and lifting height resistance. After the centrifugal pump is started, the centrifugal pump has a low head and the flow rate is very large. At this time, the pump motor (shaft The power) output is very large (according to the pump performance curve), it is easy to overload, it will damage the motor and the circuit of the pump, so the outlet valve should be closed when starting to enable the pump to run normally.
If an axial-flow pump is used, the situation is reversed. It must be a valve-opening start. At this time, the power of the motor will have a large flow due to no resistance for a short time. Pump vibration, noise, and even motor overload will often occur. Burn the motor. Close the outlet valve, which is equivalent to setting the resistance pressure manually. With the normal operation of the pump, slowly start the valve and let the pump work gradually along the regularity of its performance curve.
Two points must be ensured before starting the centrifugal pump:
1. The pump casing is filled with water in order to create 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. With the smooth start of the pump, the gate valve should be opened slowly.
Centrifugal pumps lift the water by the suction force that forms a vacuum by the centrifugal force of the impeller. Therefore, when the centrifugal pump is started, the outlet valve must be closed and the water must be poured. When the water level exceeds the impeller area and the air in the centrifugal pump is discharged, the air can be started. After the start, a vacuum is formed around the impeller and the water is sucked up, which can be automatically opened to lift the water. Therefore, the outlet valve must be closed first.
2
About centrifugal pump
Centrifugal pump is a kind of vane pump. Relying on the rotating impeller, due to the interaction between the vane and the liquid, the vane transfers the mechanical energy to the liquid, so that the pressure of the liquid can be increased to achieve the purpose of conveying the liquid. Centrifugal pump work has the following characteristics:
1 The centrifugal pump has a limit value for the head produced at a certain speed. The operating point flow rate and the shaft power are dependent on the condition of the device system connected to the pump (position difference, pressure difference and line loss). The head changes with the flow.
2 work is stable, continuous transmission, flow and pressure without pulsation.
3 Generally, there is no self-priming ability. The pump must be filled with liquid or vacuumed before starting work.
4 Centrifugal pump is started when the discharge line valve is closed. The vortex pump and axial flow pump are started when the valve is fully open to reduce the starting power.
Before the pump is started, the pump casing is filled with the liquid to be conveyed; after starting, the impeller is driven by the shaft to rotate at a high speed, and the liquid between the blades must also rotate. Under the action of centrifugal force, the liquid is thrown from the center of the impeller to the outer edge and obtains energy, leaving the outer edge of the impeller at a high speed into the scroll casing.
In the volute, the liquid is decelerated due to the gradual enlargement of the flow passage, and part of the kinetic energy is converted into static pressure energy. Finally, the liquid is discharged into the discharge pipe with higher pressure and is sent to a desired place. 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. Since the pressure above the liquid level of the reservoir 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 is constantly rotating, the liquid is continuously sucked in and discharged.
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Start of other centrifugal pumps
The above are all centrifugal pumps. For other types of pumps, the situation is as follows:
1. Axial flow pump's large flow start feature - fully open valve start
Axial pump in the zero flow conditions when the shaft power is the largest, the rated shaft power of 140% to 200%, the maximum power at the minimum flow, so in order to start the current minimum, the shaft power start-up characteristics should be a large flow start (that is, fully open Valve start).
2, start-up characteristics of mixed-flow pump - fully open valve start
When the mixed flow pump is in zero flow condition, the shaft power is between 100% and 130% of the rated power. Therefore, the start-up characteristic of the mixed flow pump should also be between the above two types of pumps. start up.
3, the starting characteristics of the vortex pump - fully open the valve to start
The vortex pump has the largest shaft power at zero flow conditions, which is 130%~190% of the rated shaft power. Therefore, similar to the axial flow pump, the start-up characteristic of the vortex pump should be a large flow start (ie, full open valve start).
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