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How to avoid some mistakes in the use of pipeline centrifugal pumps

17 Apr 2021Email

The pipeline centrifugal pump is used to transport clean water and other liquids with physical and chemical properties similar to clean water. It is suitable for industrial and urban water supply and drainage, high-rise building pressurized water delivery, garden sprinkler irrigation, fire pressurization, long-distance transportation, HVAC refrigeration cycle, Circulating pressurization of cold and warm water in bathroom and supporting equipment. In-line centrifugal pumps are the most widely used pumps in various fields. In the process of use, large and small mistakes often occur. Do you know how to avoid these?


1. The pipeline of the centrifugal pump does not match the pipeline

  Some pipeline centrifugal pump users 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 is, the greater the resistance is, so the loss head is larger, so after reducing the pipe diameter, the actual head of the pump can not 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.

   also thought that when a 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 the pipeline loss and improve the pump efficiency.  

 

2. The high-lift water pump is used for low-lift pumping

   Some pipeline centrifugal pump users believe that the lower the pumping head, the smaller the motor load. Under the misleading of this kind of misunderstanding, when purchasing a water pump, the head of the water pump is often selected very high. In fact, for centrifugal water pumps, when the pump model is determined, its power consumption is 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 and the lower the power consumption. Conversely, the lower the head, the greater the flow, and the greater the power consumption. 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 easy to be overloaded and generate heat, 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 (public number: pump housekeeper) 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 pipes of the regular high-power centrifugal pump drainage and irrigation units are equipped with gate valves. In order to reduce the motor load when the unit starts, the gate valves should be closed first, and the gate valves should be opened gradually after the motor starts.

 

3. There are many elbows on the inlet pipe of the pipeline centrifugal pump

   If many elbows are used in 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

   Doing so will cause air to accumulate in the water inlet pipe, reduce the vacuum of the water pipe and the water pump, reduce the suction lift of the water pump, and reduce 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 horizontal, and it should not be tilted upwards.  

 

5. The inlet of the pipeline centrifugal pump is directly connected to the elbow

  This will make the water flow unevenly distributed when entering the impeller through the elbow. When the diameter of the water 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 on the bottom. Otherwise, the air will gather, the water output will be reduced or the water will not be pumped, and there will be crashing noises and so on. If the diameter of the water inlet pipe and the water inlet of the water pump are equal, a straight pipe should be added between the water inlet of the water 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.  

 

6. The outlet of the pipe centrifugal pump is above the normal water level of the outlet pool

   If the water 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. 

 

7. The position of the water inlet of the water inlet pipe is wrong

  ①The distance between the inlet of the inlet pipe and the bottom and wall of the inlet pool is less than the diameter of the 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 or suction of mud and sand debris during pumping, which will block the water inlet.

  ②When 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 intake 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-scale pumps should not be less than 600-1000mm.

 

8. When setting the bottom valve, the bottom section of the inlet pipe is not vertical

   If installed like this, 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°.

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