Common Mistakes in the Use of Pipeline Pumps (86 views)
26 Apr 2023 08:45
1、 Pipeline matching of pipeline centrifugal pump
Some pipeline centrifugal pump users believe that this can increase the actual head, but in fact, the actual head of the water pump is equal to the total head to the loss head. After the water pump model is determined, the total head is fixed; The loss of head mainly comes from pipeline resistance. The smaller the pipe diameter, the greater the resistance, and therefore the greater the loss of head. Therefore, reducing the pipe diameter not only does not increase the actual head of the water pump, but also reduces it, leading to a decrease in pump efficiency. Similarly, when a small diameter water pump uses a large water pipe for pumping, the actual head of the pump will not be reduced. Instead, the loss head will be reduced due to the decrease in pipeline resistance, resulting in an increase in actual head. Organic experts also believe that when small diameter water pumps use large water pipes for pumping, it will inevitably greatly increase the motor load. They believe that as the pipe diameter increases, the pressure of the water in the outlet pipe on the pump impeller will increase, thus greatly increasing the motor load. Little did they know that the magnitude of liquid pressure is only related to the height of the head, and is not related to the cross-sectional area of the water pipe. As long as the lift is constant, the size of the impeller of the water pump remains unchanged, and the pressure acting on the impeller is constant regardless of the pipe diameter. However, as the pipe diameter increases, the water flow resistance will decrease, resulting in an increase in flow rate and an appropriate increase in power consumption. But as long as it is within the rated head range, the water pump can work normally no matter how the pipe diameter is increased, and it can also reduce pipeline losses and improve pump efficiency.
2、 High head water pump for low head pumping
Some pipeline centrifugal pump users believe that the lower the pumping head, the smaller the motor load. Under the misleading misconception, when choosing a water pump, the head of the pump is often chosen too high. In fact, for centrifugal pumps, when the pump model is determined, the power consumption is directly proportional to the actual flow rate of the pump. The flow rate of the water pump will decrease with the increase of the head, so the higher the head, the smaller the flow rate, and the smaller the power consumption. On the contrary, the lower the head, the greater the flow, and the greater the power consumed. Therefore, in order to prevent motor overload, it is generally required that the actual pumping head of the water pump should not be less than 60% of the rated head. So when high head is used for low head pumping, the motor is prone to overload and heat, and in severe cases, it can burn out the motor. In case of emergency use, a gate valve (or block the small water outlet with wood, etc.) must be installed on the water outlet pipe to reduce the flow (official account number: pump steward) and prevent motor overload. Pay attention to the temperature rise of the motor. If the motor is found to be overheated, the water outlet flow should be reduced or the machine should be shut down in a timely manner. This is also prone to misunderstandings. Some operators believe that blocking the water outlet and forcibly reducing the flow rate will increase the motor load. In fact, on the contrary, the outlet pipes of regular high-power centrifugal pump irrigation and drainage units are equipped with gate valves. In order to reduce the motor load during unit startup, the gate valve should be closed first, and gradually opened after the motor starts. This is the reason.
3、 There are many elbows on the inlet pipeline of the pipeline centrifugal pump
If too many elbows are used on the inlet pipeline, it will increase local water flow resistance. And the elbow should turn in the vertical direction, and it is not allowed to turn in the horizontal direction to avoid gathering air.
4、 When installing the water inlet pipeline, the horizontal section should be horizontal or tilted upwards
This will cause air to accumulate in the inlet pipe, reduce the vacuum degree of the water pipe and water pump, reduce the suction head of the water pump, and reduce the water output. The correct approach is to tilt the horizontal section slightly towards the direction of the water source, not horizontally, and not upward.
5、 The inlet of the pipeline centrifugal pump is directly connected to the elbow
This will cause uneven distribution of water flow through the elbow and into the impeller. When the diameter of the inlet pipe is greater than that of the water pump inlet, an eccentric reducing pipe should be installed. The flat part of the eccentric reducer should be installed above, and the inclined part should be installed below. Otherwise, air will accumulate, water output will decrease or water cannot be pumped, and there will be a sound of impact. If the diameter of the inlet pipe is equal to that of the water pump inlet, a straight pipe should be added between the water pump inlet and the elbow, and the length of the straight pipe should not be less than 2-3 times the diameter of the water pipe.
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