Misunderstandings in the use of centrifugal pumps
1. High-lift pumps are used for low-lift pumping. Many operators believe that the lower the pumping head, the smaller the motor load. Under the misleading of this kind of misunderstanding, when buying a water pump, the head of the water pump is often selected very high. In fact, for centrifugal pumps, when the pump model is determined, its power consumption is proportional to the actual flow 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 and the lower the power consumption. Conversely, the lower the head, the greater the flow, and the greater the power consumed. Therefore, in order to prevent the motor from overloading, it is generally required that the actual pumping head of the pump should not be less than 60% of the calibrated head. Therefore, when the high head is used for pumping water with a low head, the motor is easily overloaded and heats up, and it can burn the motor in severe cases. In case of emergency use, a gate valve for adjusting the amount of water must be installed on the outlet pipe (or block the small outlet with wood, etc.) to reduce the flow and prevent the motor from overloading. Pay attention to the temperature rise of the motor. If the motor is overheated, turn off the water outlet flow or shut down in time. This is also easy to misunderstand. Some operators think that blocking the water outlet and forcibly reducing the flow will increase the motor load. In fact, the opposite is true. The outlet pipe of a regular high-power centrifugal pump drainage and irrigation unit is equipped with a gate valve. In order to reduce the motor load when the unit starts, the gate valve should be closed first and then gradually opened after the motor starts.
2. Large-caliber water pump with small water pipe for pumping. Many operators think that this can increase the actual head. In fact, the actual head of the pump = total head ~ loss head. When the pump model is determined, the total head is fixed; the loss head mainly comes from the pipeline resistance. The smaller the pipe diameter, the greater the resistance, and the greater the loss head. Therefore, after the pipe diameter is reduced, the actual head of the water pump cannot be increased. , On the contrary, it will decrease, resulting in a decrease in the efficiency of the water pump. In the same way, when a small-diameter water pump uses a large water pipe to pump water, the actual head of the pump will not be reduced. On the contrary, the loss of the head will be reduced due to the decrease in the resistance of the pipeline, and the actual head will be increased. They also think that when the small diameter water pump uses a large water pipe to pump water, it will inevitably increase the motor load. They believe that as the pipe diameter increases, the water in the outlet pipe will exert greater pressure on the pump impeller, which will greatly increase the motor load. As everyone knows, the size of the liquid pressure is only related to the height of the head, and has nothing to do with the cross-sectional area of the water pipe. As long as the head is constant, the size of the impeller of the pump remains the same, and the pressure acting on the impeller is constant regardless of the pipe diameter. Only after the pipe diameter increases, the water flow resistance will decrease, and the flow will increase, and the power consumption will also increase appropriately. But as long as it is within the rated head range, the pump can work normally no matter how the pipe diameter is increased, and it can also reduce pipeline losses and improve pump efficiency.
3. There are many elbows used on the water inlet pipe. If there are too many elbows on the water inlet pipe, it will increase the 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 pipe, the horizontal section is horizontal or upward. This will cause air to collect in the water inlet pipe, reduce the vacuum of the water pipe and the water pump, and reduce the suction lift of the water pump and the water output. The correct approach is: its horizontal section should be slightly inclined towards the direction of the water source, it should not be level, let alone tilt upward.
5. The bottom section of the inlet pipe with the bottom valve is not vertical. If installed in this way, the valve cannot close by itself, causing water leakage. The correct installation method is: the inlet pipe equipped with a bottom valve, the bottom section is best to be vertical. If it cannot be installed vertically due to topographical conditions, the angle between the axis of the water pipe and the horizontal plane should be above 60°.
6. The water inlet of the water pump is directly connected with the elbow, which will cause uneven distribution of water flow through the elbow and into the impeller. When the diameter of the inlet pipe is larger than the water inlet of the pump, an eccentric reducing pipe should be installed. The flat part of the eccentric reducer should be installed on the top, and the inclined part should be installed below. Otherwise, the air will gather, the water output will be reduced or the water will not be able to be pumped, and there will be impact noises. If the diameter of the water inlet pipe and the water inlet of the pump are the same, a straight pipe should be added between the water inlet of the pump and the elbow. The length of the straight pipe shall not be less than 2 to 3 times the diameter of the water pipe.
7. The position of the water inlet of the water inlet pipe is wrong (1) The distance between the water inlet of the water inlet pipe and the bottom and wall of the water inlet is less than the diameter of the water inlet. If there is dirt such as mud and sand at the bottom of the pool, and the distance between the water inlet and the bottom of the pool is less than 1.5 times the diameter, it will cause poor water intake during pumping or suction of mud and sand debris and block the water inlet. (2) When the water inlet depth of the water inlet pipe is not enough, this will cause vortexes on the water surface around the water inlet pipe, which will affect the water inlet and reduce the water output. The correct installation method is: the depth of the medium and small pumps should not be less than 300～600mm, and the large pumps should not be less than 600～1000mm.
8. The outlet of the water outlet is above the normal water level of the outlet pool. If the outlet is above the normal water level of the outlet pool, although the pump lift is increased, the flow rate is reduced. If the water outlet must be higher than the water level of the pool due to terrain conditions, elbows and short pipes should be installed at the nozzle to make the water pipe a siphon type and reduce the height of the water outlet.
