Diwei Water shares some common mistakes made during the selection, installation, and use of pumps.

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

If the outlet is above the normal water level of the outflow pond, although the pump head is increased, the flow rate is reduced. If the outlet must be higher than the pond level due to terrain constraints, a bend and a short pipe should be installed at the pipe mouth to make the water pipe siphon-like, thereby lowering the outlet height.

Improper location of the water intake for the inlet pipe

The inlet of the water intake pipe is less than the diameter of the intake diameter from the bottom and side walls of the intake pool. If there is mud and sand or other debris at the bottom of the pool, the distance from the intake to the pool bottom is less than 1.5 times the diameter, it can cause poor water flow or suction in mud and debris during pumping, which may block the intake.

(2) If the water inlet depth of the intake pipe is insufficient, it can cause whirlpools around the intake pipe, affecting water intake and reducing output. The correct installation method is: the water intake depth for small and medium-sized pumps should not be less than 300-600mm, and for large pumps, not less than 600-1000mm.

Section below the bottom valve of the inlet pipe is not vertical.

If installed this way, the valve cannot close automatically, leading to water leakage. The correct installation method is: for the incoming water pipe equipped with a bottom valve, the bottom section should be as vertical as possible. If it is not possible to install vertically due to topographical conditions, the angle between the water pipe axis and the horizontal plane should be 60° or more.

Section 4: Direct Connection of Pump Inlet to Elbow

This can cause uneven distribution of water flow as it passes through the elbow into the impeller. When the diameter of the inlet pipe is larger than the pump's inlet, an eccentric reducer should be installed. The flat section of the reducer should be mounted on top, and the sloped section on the bottom. Otherwise, air may accumulate, resulting in reduced water output or failure to pump water, along with knocking sounds. If the diameter of the inlet pipe is equal to the pump's inlet, a straight pipe should be added between the pump's inlet and the elbow, with a length not less than 2 to 3 times the diameter of the pipe.

Five: There are many elbows used in the water supply pipeline.

If there are many elbows in the water intake pipeline, it will increase the local water flow resistance. Moreover, elbows should turn vertically; horizontal turns are not permitted to avoid air accumulation.

Six: During the installation of the water supply pipeline, the horizontal section should be level or slightly upward.

This action causes air to accumulate in the intake pipe, reducing the vacuum level of the water pipes and pump, leading to a decrease in the pump's water lift height and reduced water flow. The correct procedure is: the horizontal section should be slightly inclined towards the water source, rather than being level, let alone arched upwards.

Section 7: Large diameter pump with small water pipes for water extraction

Many users believe that this can increase the actual head of the pump, but in fact, the actual head of the pump equals the total head minus the loss head. Once the pump model is determined, the total head is fixed; the loss head mainly comes from pipeline resistance, and obviously, the smaller the pipe diameter, the greater the resistance, resulting in a higher loss head. Therefore, reducing the pipe diameter does not increase but actually decreases the actual head of the pump, leading to a decrease in pump efficiency. Similarly, when a small-diameter pump is used to draw water through a large pipe, it does not reduce the actual head of the pump but, due to the reduced pipeline resistance, decreases the loss head, thus slightly increasing the actual head. Some users also believe that using a small-diameter pump with a large pipe will significantly increase the motor load. They think that as the pipe diameter increases, the pressure on the pump impeller from the water in the outlet pipe increases, thus greatly increasing the motor load. However, the pressure of the liquid is only related to the head, not the cross-sectional area of the pipe. As long as the head remains constant, and the impeller size of the pump does not change, the pressure exerted on the impeller is constant regardless of the pipe diameter. The only thing is that as the pipe diameter increases, the flow resistance decreases, slightly increasing the flow rate and the energy consumption. Yet, within the rated head range, increasing the pipe diameter will allow the pump to operate normally, and it can also reduce pipeline losses and improve pump efficiency.

High-head pump for low-head pumping

Many novices believe that the lower the pump's head, the smaller the motor load. Under this mistaken belief, when selecting a pump, they often choose a pump with a higher head. In reality, for centrifugal pumps, once 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 decreases as the head increases, so a higher head results in a smaller flow rate and, consequently, lower power consumption. Conversely, a lower head results in a larger flow rate and, therefore, higher power consumption. To prevent motor overload, it is generally required that the actual pump head used for water extraction not be less than 60% of the rated head. Therefore, when a high-head pump is used for low-head water extraction, the motor is prone to overload and overheating, which can lead to motor damage. If emergency use is necessary, a regulating gate valve (or use wood or other materials to block the small outlet) must be installed on the discharge pipe to reduce the flow rate and prevent motor overload. Pay attention to the motor temperature rise; if the motor overheats, reduce the flow rate at the outlet or shut down the motor promptly. This is also a common misconception; some operators believe that blocking the outlet to force a reduction in flow increases the motor load. In fact, the opposite is true. On regular high-power centrifugal pump irrigation and drainage units, the discharge pipes are equipped with gate valves. To reduce the motor load during startup, the valves should be closed first, and then gradually opened after the motor starts, which is the principle behind this.