Analysis of various misunderstandings that often occur in the use of centrifugal pumps

1. High-lift water pump is 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 purchasing a water pump, the head of the water pump is often selected very high. In fact, for centrifugal pumpsChina DC Water Pumps Suppliers, when the pump model is determined, the 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 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 easily overloaded and heats up, and it can burn the motor in severe cases. If it is used in emergency, a gate valve for adjusting the water output must be installed on the outlet pipe (or a small water outlet should be blocked 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 diameter water pump with small water pipe for pumping water

Many operators think that this can increase the actual head, but the actual head of the water 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, and the greater the loss head is. Therefore, after the pipe diameter is reduced, the actual head of the 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 no matter how large the pipe diameter is. 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. When installing the water inlet pipe, the horizontal section is horizontal or upward

Doing so will cause air to gather 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 level, let alone tilt upward.

4. There are many elbows used on the inlet pipe

If more elbows are used on the 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.

5. The pump inlet 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 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.

6. The bottom section of the inlet pipe equipped with a 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°.

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

(1) The distance between the inlet of the inlet pipe and the 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 debris during pumping, which will 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 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.