Croos Pump (Shanghai) Co., Ltd.

Analysis of Various Misunderstandings in the Use of Centrifugal Pumps

1. Low lift operation of high lift water pump

Many people think that the lower the lift, the lower the motor load. In the misleading of this false knowledge, when the water pump is selected, the pump's lift is often high. In fact, for centrifugal pumps, when the pump model is determined, the power consumption is proportional to the actual flow of the pump. The flow of the pump decreases with the increase of the lift, the higher the lift, the smaller the flow and the less power consumed. Conversely, the lower the head, the larger the flow, the greater the power consumption.

Therefore, in order to prevent the motor overload, it is generally required that the actual pumping use of the pump shall not be less than 60% of the nominal lift. When the high lift is used to pump water too low, the motor is overloaded and hot, which can burn the motor. Emergency use must adjust the water flow gate valve on the outlet pipe to reduce the flow and prevent motor overload.

Pay attention to the temperature rise of the motor. If the motor is too hot, we should turn off the small outlet flow or shutdown. This can also be misleading, with some players thinking that blocking the outlet and forcing down the flow will increase the load on the motor. In fact, the opposite is true. The normal high power centrifugal pump discharge line is equipped with gate valves. In order to reduce the motor load at the start of the unit, the gate valve should be closed first and the gate valve will be opened gradually after the motor starts.

2. Large diameter water pump with small pipe pumping

Many users think this can improve the actual lift, actually the actual lift of the pump = total head lift - loss of lift. When the horizontal centrifugal pump model is determined, the head lift is certain; The loss of the lift mainly comes from pipeline resistance. The smaller the diameter of the pipe, the greater the resistance is. Therefore, after reducing the pipe diameter, the actual lift of the pump will not increase but decrease, resulting in the decrease of water pump efficiency.

In the same way, when the small diameter water pump is pumped, it will not lower the actual lift of the pump, but it will reduce the loss due to the decrease in the resistance of the pipe, which will improve the actual lift. There are also users who believe that small pipe diameter pumps will greatly increase the load of the motor when pumping water. They think that when the diameter of the pipe increases, the water in the pipe will be more pressure on the pump impeller, which will greatly increase the load of the motor.

It is not known that the size of the liquid pressure is related to the height and height of the head, but not the size of the area. As long as the lift is certain, the impeller size of the pump is the same, regardless of the size of the tube, the pressure on the impeller is certain. As the diameter increases, the flow resistance decreases, and the flow rate increases, and the power consumption increases appropriately. However, as long as the water pump is increased in the range of the rated lift, it is possible to work normally, and it can reduce pipe loss and improve water pump efficiency.

3. The pipe section of the inlet pipe is too flat or upturned

This will bring the air into the water pipe and reduce the vacuum of the water pipe and water pump, so that the water will be lowered and the amount of water will be reduced. The correct approach is that the horizontal section should be slightly inclined to the direction of the water, and it should not level, not even upward tilt.

4. The inlet pipe bends too much

If you use more elbow on the inlet, you will increase the resistance of local water flow. And the elbow should turn in the vertical direction, not allowing the turn in the horizontal direction to avoid the accumulation of air.

5. The water pump inlet and bend are directly connected

This makes the water flow unevenly through the elbow and into the impeller. Eccentric reducer should be installed when the inlet pipe is larger than the pump inlet. The eccentric tapered section shall be mounted on top, and the inclined plane shall be mounted below. Otherwise, the air will gather, and the water output is reduced, or the water can not be pumped, and there is a crash sound. If the inlet pipe is equal to the diameter of the water pump inlet, the pipe should be kept between the inlet and the bend of the pump. The length of the straight pipe shall not be less than 2 ~ 3 times the diameter of the pipe.

6. The bottom end of the inlet pipe is not perpendicular

In this way, the valve cannot shut itself down and will cause a leak. The proper installation method is that the inlet pipe with bottom valve preferably vertical in the next section. If because of the terrain conditions, it cannot be installed vertically, the pipe axis and horizontal plane angle should be in more than 60 °.

7. The inlet position of the inlet pipe is not correct

The inlet of the inlet pipe is less than the inlet diameter of the inlet and the wall of the water inlet. If there is dirt and dirt at the bottom of the pool, the water inlet is less than 1.5 times the distance from the bottom of the pool, it will cause the water to be blocked or absorbed into the water to fill the inlet.

When the inlet of the inlet pipe is not enough depth, it will cause a vortex of water around the inlet, and it will affect the water and reduce the amount of water. The correct installation method is that the water depth of the small and medium water pump shall not be less than 300 ~ 600 mm, and the large pump shall not be less than 600 ~ 1000 mm.

8. The outlet is above normal water level

If the outlet is above the normal water level of the tank, although it increases the lift of the pump, it reduces the flow rate. If the water level of the outlet must be higher than the water level due to the topography condition, the pipe should be installed with elbow and short pipe, so that the pipe will become siphon and reduce the outlet height.

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