01 High lift pump running at low load

Many people believe that the lower the pumping head, the smaller the motor load. Under this misconception, when choosing a pump, the head of the pump is often chosen to be very high. In fact, for a positive displacement pump, when the pump model is determined, the power consumption is directly proportional to the actual flow rate of the pump. The flow rate of the pump will decrease with the increase of head, so the higher the head, the smaller the flow rate, and the lower the power consumption. On the contrary, 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 calibrated head. When high head is used for low head pumping, the motor may overload and generate heat, which can seriously burn out the motor. For emergency use, a gate valve must be installed on the outlet pipe to adjust the water flow rate and prevent motor overload.

Pay attention to the temperature rise of the motor. If the motor is found to be overheated, the outlet flow rate should be reduced or the machine should be shut down in a timely manner. This can also easily lead to misunderstandings. Some operators believe that blocking the water outlet and forcibly reducing the flow rate will increase the motor load. In fact, on the contrary, the outlet pipes of regular high-power centrifugal pump irrigation units are equipped with gate valves. In order to reduce the motor load during unit startup, the gate valves should be closed first, and gradually opened after the motor starts. This is the principle.

02 Large caliber pump with small water pipe for pumping

Many users believe that this can increase the actual head, but in fact, the actual head of the pump is equal to the total head minus the loss head. After the pump model is determined, the total head is fixed; The loss of head mainly comes from pipeline resistance. The smaller the pipe diameter, the greater the resistance, resulting in a greater loss of head. Therefore, reducing the pipe diameter not only fails to increase the actual head of the pump, but also reduces it, leading to a decrease in pump efficiency.

Similarly, when a small diameter pump uses a large water pipe to pump water, the actual head of the pump will not be reduced. Instead, the loss head will be reduced due to the decrease in pipeline resistance, resulting in an increase in the actual head. Some users also believe that when a small diameter pump uses a large water pipe to pump water, it will inevitably greatly increase the motor load. They believe that as the pipe diameter increases, the pressure of the water in the outlet pipe on the pump impeller will increase, thus greatly increasing the motor load.

Little did they know that the magnitude of liquid pressure is only related to the head, and not to the cross-sectional area of the water pipe. As long as the head is constant and the impeller size of the pump remains unchanged, the pressure acting on the impeller remains constant regardless of the diameter of the pipe. However, as the diameter of the pipe increases, the water flow resistance will decrease, resulting in an increase in flow rate and a moderate increase in power consumption. 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

03 The horizontal section of the inlet pipeline is too straight or upturned

This will cause air to accumulate in the inlet pipe, reduce the vacuum level of the water pipe and pump, lower the suction head of the pump, and decrease the water output. The correct approach is that the horizontal section should be slightly inclined towards the direction of the water source, not horizontal, let alone upward.

04 Too many bends in the inlet pipeline

If more elbows are used on the inlet pipeline, it will increase local water flow resistance. And the elbow should turn in the vertical direction, not in the horizontal direction, to avoid gathering air.

05 The pump inlet is directly connected to the elbow

This will cause uneven distribution of water flow when it enters the impeller through the elbow. When the diameter of the inlet pipe is larger than that of the pump inlet, an eccentric variable diameter pipe should be installed. The flat part of the eccentric variable diameter pipe should be installed on top, and the inclined part should be installed on the bottom. Otherwise, the air will gather, the water output will decrease or the water cannot be pumped out, and there will be collision sounds. If the diameter of the inlet pipe is equal to that of the pump inlet, a straight pipe should be added between the pump inlet and the elbow, and the length of the straight pipe should not be less than 2-3 times the diameter of the water pipe.

06 The bottom end of the inlet pipe of the bottom valve is not vertical

This installation prevents the valve from closing on its own, causing water leakage. Correct installation method: For inlet pipes with bottom valves, it is best to have the bottom section vertical. If vertical installation is not possible due to terrain conditions, the angle between the axis of the water pipe and the horizontal plane should be at least 60 °.

07 The inlet position of the inlet pipe is incorrect

The 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 are sediment and other pollutants at the bottom of the pool, and the distance between the inlet and the bottom of the pool is less than 1.5 times the diameter, it will cause poor water intake or suction of sediment and debris during pumping, blocking the inlet.

When the water inlet of the inlet pipe is not deep enough, it will cause vortices on the water surface around the inlet pipe, affecting the water intake and reducing the water output. The correct installation method is that the water inlet depth of small and medium-sized pumps should not be less than 300-600mm, and that of large pumps should not be less than 600-1000mm.

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

If the outlet is above the normal water level of the water tank, although it increases the pump head, it reduces the flow rate. If due to terrain conditions, the outlet must be higher than the water level of the outlet pool, then elbows and short pipes should be installed at the pipe mouth to make the water pipe siphon and reduce the height of the outlet.