There are three main pipeline centrifugal pump performance curve curve: flow - head curve, traffic - power curve, traffic - efficiency curve.
A, flow - head characteristic curve
It is the basic of centrifugal pump performance curve. Specific speed is less than 80 of the centrifugal pump has the characteristics of rising and falling (curved) under both raised among, both sides, said hump performance curve. Specific speed centrifugal pump has between 80 ~ 150 flat performance curve. Than revolutions in the more than 150 centrifugal pump has a steep fall in the performance curve. Generally said, when the traffic hours, head high, with the increase of traffic head will gradually decline.
B, flow - power curve
Shaft power is increases with flow rate, when the flow rate Q = 0, the corresponding shaft power is not equal to zero, and to a certain value (about 60% of the earth's normal operation). The main power consumption on the mechanical loss. Is full of water in the pump at this time, if the long run, will lead to pump temperature rising, the pump shell, bearing will be fever, serious when can make the pump body thermal deformation, we called "stuffy head", the head of the maximum, when gradually open the discharge valve, the flow rate will gradually increase, shaft power also slowly increase.
C, flow - efficiency curve
Xiangshan head shape, its curve when the flow rate is zero, efficiency is also equal to zero, with the increase of flow rate, efficiency is also increased gradually, but efficiency has decreased after increased to a certain value, there is a high efficiency, near the highest efficiency point, efficiency is high, the region known as the high efficiency area
Eight pipeline centrifugal pump use erroneous zone
A, pipeline centrifugal pump pipe way of matching
Some pipeline centrifugal pump users think it can improve the actual lift, but the actual head loss = total head ~ head of pump. When the water pump model is determined, the total head is certain; Head loss mainly comes from the pipeline resistance, the smaller the diameter is obviously the greater the resistance, and therefore the greater the loss of head, so reduce the pipe diameter, the actual head of pump instead of increased, it will reduce, to lower the pump efficiency. By the same token, when small diameter water pump with large water pumping, also won't erode the real value of the pump head, may because of the line in order to reduce the loss of the head with the decrease of the resistance, the actual lift have improved. There is also a machinist think small diameter water pump with large water pumping, will greatly increase the motor load, after they think diameter increases, the water in the outlet pipe of pump impeller pressure is big, so will greatly increase the motor load. Little imagine, the size of the liquid pressure only associated with head high and low, and have nothing to do with the size of the pipe sectional area. As long as the head must be, water pump impeller size remains the same, no matter how big pipe diameter, pressure effect on the impeller is certain. Just pipe diameter increases, the flow resistance will decrease, and make the flow rate increases, power consumption are increasing. But as long as within the scope of rated head, no matter how to increase the pump diameter can be normal work, and also can reduce line losses, improve the efficiency of the pump.
Second, high lift water pump used for low-lift pumping
Some pipeline centrifugal pump users think the lower water head, the smaller the motor load. Under this false understanding of misleading when water pump of choose and buy, often the selection of the pump head high. In fact for the centrifugal pump, when the water pump model is determined, the size of the consumed power is proportional to the actual flow pump. And pump flow will decrease with the increase of the head, and the higher the head, the smaller the flow, and the smaller power consumption. Conversely, the lower the head, flow rate, the greater the consumption of power. Therefore, in order to prevent the motor overload, general requirements the actual water use head of the pump shall not be less than 60% of the labeling head. So when the high-lift pump used for low head pumping motor easy to overload and fever, serious when can burning motor. If emergency use, must be in the outlet pipe with a gate valve is used to adjust the water yield (or use the content such as wood wall small outlet), to reduce the flow, to prevent the motor overload. Pay attention to the motor temperature rise, if discover motor overheating, should be timely down outlet flow or turn it off. It is also easy to produce misunderstanding, some machinist think blocking outlet, forced to reduce traffic, can increase the motor load. In fact just the opposite, formal power centrifugal pump irrigation and drainage units are fitted on the outlet pipe of gate valve, in order to reduce the unit startup motor load, should be closed gate, after waiting for motor start and gradually open the gate.
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