The high head water pump is used for low head water pumping
Many people believe that the lower the water pumping head, the smaller the motor load. Under the influence of this misconception, when purchasing water pumps, the pumping head is often selected very high. In fact, for centrifugal pumps, once the pump model is determined, the power consumption is proportional to the actual flow rate of the pump. The flow rate of the pump decreases as the head increases, so the higher the head, the smaller the flow rate, and the lower the power consumption. Conversely, the lower the head, the greater the flow rate, and the greater the power consumption.
Therefore, to prevent motor overload, it is generally required that the actual pumping head of the pump should not be less than 60% of the rated head. Therefore, when a high head pump is used for low head water pumping, the motor is prone to overload and overheating, and in severe cases, the motor may be burnt out. In emergency situations, a valve (or wooden block, etc.) should be installed on the outlet pipe to adjust the water flow and reduce the flow rate to prevent motor overload. Pay attention to the temperature rise of the motor. If the motor is found to be overheating, adjust the flow rate of the outlet or shut down the motor in time.
Some operators may misunderstand that blocking the outlet and forcibly reducing the flow rate will increase the motor load. In fact, it is just the opposite. Regular high-power centrifugal pump drainage units are equipped with valves on the outlet pipe. To reduce the motor load when the unit starts, the valve should be closed first, and then gradually opened after the motor starts. This is the principle.
Large diameter pumps with small pipes for water pumping
Many users believe that this can increase the actual head. In fact, the actual head of the pump = total head - loss head. Once the pump model is determined, the total head is fixed;
The loss head mainly comes from pipeline resistance, and the smaller the pipe diameter, the greater the resistance, resulting in a greater loss head. Therefore, reducing the pipe diameter will not increase the actual head of the pump, but will decrease it, resulting in a decrease in pump efficiency.
Similarly, when a small diameter pump is used to pump water with a large diameter pipe, it will not reduce the actual head of the pump, but will increase it because the resistance of the pipeline decreases, reducing the loss head and increasing the actual head of the pump. Some users believe that when a small diameter pump pumps water with a large diameter pipe, it will greatly increase the motor load. They believe that after the diameter of the pipe increases, the pressure of the water in the outlet pipe on the impeller of the pump will increase, thereby greatly increasing the motor load.
Little do they know that the magnitude of liquid pressure is only related to the head, not the size of the pipe cross-section. As long as the head is constant and the impeller size of the pump remains unchanged, regardless of the pipe diameter, the pressure acting on the impeller is constant. It is just that after the pipe diameter increases, the water flow resistance decreases, causing the flow rate to increase and the power consumption to increase appropriately.
However, as long as the pump can work normally within the rated head range, regardless of the pipe diameter, it can work normally, and it can also reduce pipeline losses and improve pump efficiency.
When installing the inlet pipe, the horizontal section is horizontal or upward
Doing so will cause air to accumulate in the inlet pipe, reduce the vacuum of the pipe and the pump, and reduce the suction head of the pump, resulting in a decrease in the flow rate.
The correct method is: the horizontal section of the inlet pipe should be slightly inclined towards the water source direction, not horizontal, let alone upward.
There are many elbows on the inlet pipe
If there are many elbows on the inlet pipe, it will increase local water flow resistance. And the elbow should turn vertically, and it is not allowed to turn horizontally to avoid air accumulation.
The inlet of the water pump is directly connected to the elbow
Doing so will cause uneven distribution of water flow when the water flows through the elbow into the impeller. When the diameter of the inlet pipe is greater than the inlet of the water pump, an eccentric reducer should be installed. The flat part of the eccentric reducer should be installed on the top, and the inclined surface should be installed on the bottom. Otherwise, air will accumulate, the water output will decrease or fail to pump water, and there will be impact noise, etc. When the diameter of the inlet pipe is equal to the inlet of the water pump, a straight pipe should be installed between the inlet of the water pump and the elbow, and the length of the straight pipe should not be less than 2-3 times the diameter of the pipe.
The lowest section of the inlet pipe with a check valve is not vertical
If installed like this, the valve cannot close by itself, causing water leakage. The correct installation method is: the lowest section of the inlet pipe with a check valve should preferably be vertical. If it is not possible to install it vertically due to terrain conditions, the angle between the axis of the pipe and the horizontal plane should be above 60°.
The position of the inlet of the inlet pipe is incorrect
(1) The distance between the inlet of the inlet pipe and the bottom and wall of the inlet tank is less than the diameter of the inlet. If there are sediment and other pollutants on the bottom of the tank, when the distance between the inlet and the bottom of the tank is less than 1.5 times the diameter, it will cause poor water intake or suction of sediment and debris, blocking the inlet.
(2) When the depth of the inlet of the inlet pipe is not enough, this will cause eddies around the inlet of the inlet pipe, affecting water intake and reducing water output. The correct installation method is: the depth of the inlet of the medium and small pumps should not be less than 300-600mm, and that of large pumps should not be less than 600-1000mm.
The outlet of the outlet pipe is above the normal water level of the outlet tank
If the outlet is above the normal water level of the outlet tank, although the pump head is increased, the flow rate is reduced. If the outlet must be above the water level of the outlet tank due to terrain conditions, elbows and short pipes should be installed at the outlet to reduce the outlet height and make the pipe a siphon type to reduce the outlet height.
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