Do You Know The Six Misunderstandings In The Use Of Centrifugal Pumps?

Aug 29, 2020


When installing the inlet pipe,

Horizontal section horizontal or upward

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 below. Otherwise, the air will gather, the water output will be reduced or the water will not 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.


Large diameter water pump with small water pipe for pumping

High-lift pumps are used for low-lift pumping.


The pump inlet is directly connected to the elbow

(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 and other dirt 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.

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°.

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.

If more elbows are used in 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.

(2) When the water inlet of the water inlet pipe is not deep enough, this will cause vortexes on the water surface around the water inlet pipe, which will affect the water intake. This is how the car "skin disease" can be solved and the water output can be reduced. 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.

Many QBY pneumatic diaphragm pump 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 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 too low head, the motor is easy to be overloaded and generate heat. In severe cases, the motor can be burnt. 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 rate and prevent the motor from overloading. Pay attention to the temperature rise of the motor. If you find that the motor is overheated, you should turn off the water outlet or shut down in time.

This is also prone to misunderstanding. Some operators think that blocking the water outlet and forcibly reducing the flow will increase the load of the motor. There are several major misunderstandings in the use of automobile lubricants. In fact, the opposite is true. The outlet pipes of 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 valve should be closed first, and then the gate valve should be gradually opened after the motor starts.


The outlet pipe is above the normal water level of the outlet pool

The bottom section of the inlet pipe with the bottom valve is not vertical.


There are many elbows used on the inlet pipe

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.


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

Many pilots 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 pipeline resistance. The smaller the pipe diameter, the greater the resistance, so the greater the loss head, the analysis of the cause of the corrosion of stainless steel, so after reducing the pipe diameter, the pump Instead of increasing the actual head, it will decrease, resulting in a decrease in pump efficiency.

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, but the loss 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 a small pipe diameter water pump uses a large 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.