Multistage Centrifugal Pump Pipeline Division Match

One, multi-stage centrifugal pump pipeline department matching

Some multi-stage centrifugal pump users believe that reducing the pipe diameter can improve the practical head, but in fact, the practical head of the pump = total head - loss head. Once the pump type is determined, the total head is fixed; the loss head mainly comes from the pipeline resistance, and the smaller the pipe diameter, the greater the resistance, resulting in a larger loss head. Therefore, reducing the pipe diameter does not increase but actually decreases the practical head of the pump, leading to a decrease in pump efficiency. Similarly, when a small-diameter pump is used to pump water through a large pipe, it will not decrease the practical head of the pump; instead, it will reduce the loss head due to the decreased pipeline resistance, thereby slightly improving the practical head. Some operators also believe that using a small-diameter pump with a large pipe will significantly increase the motor load, thinking that with the increased pipe diameter, the water pressure on the pump impeller will be greater, thus increasing the motor load. However, the pressure of the liquid is only related to the height of the head and has nothing to do with the size of the pipe cross-section. As long as the head is fixed and the impeller size of the pump remains unchanged, the pressure acting on the impeller is constant regardless of the pipe diameter. The only thing is that when the pipe diameter increases, the flow resistance decreases, resulting in an increase in flow rate and a slight increase in power consumption. But within the extra head range, regardless of how the pipe diameter increases, the pump can still operate normally, and it can also reduce pipeline losses and improve pump efficiency.

High-head pump for low-head water pumping

Some multi-stage centrifugal pump users mistakenly believe that the lower the water lifting height, the smaller the motor load. Under this misconception, when selecting a pump, they often choose a pump with a high water lifting height. In fact, for centrifugal pumps, once the pump type is determined, the power consumption is directly proportional to the actual flow rate of the pump. As the water lifting height increases, the flow rate of the pump decreases, so the higher the water lifting height, the smaller the flow rate, and the lower the power consumption. Conversely, the lower the water lifting height, the greater the flow rate, and the higher the power consumption. Therefore, to prevent motor overload, the actual water lifting height of the pump should not be less than 60% of the rated water lifting height. Thus, when high water lifting height is used for low water lifting height, the motor is prone to overload and overheating, which can even lead to motor damage. In case of emergency use, a throttle valve on the discharge pipe (or using a wooden plug to block a small discharge opening) should be installed to reduce the flow rate and prevent motor overload. Pay attention to the motor temperature rise, and if the motor overheats, reduce the flow rate at the discharge opening or shut down the motor promptly. This point is also easily misunderstood; some operators believe that blocking the discharge opening and forcing a reduction in flow will increase the motor load. However, this is exactly the opposite. Standard high-power centrifugal pump irrigation and drainage units are equipped with throttle valves on the discharge pipes. To reduce the motor load during the start-up of the unit, the throttle valve should be closed first, and then gradually opened after the motor starts, which is the principle behind this.

Three: Multiple elbows on the inlet pipeline of the multi-stage centrifugal pump

If there are many elbows in the inlet pipeline, it will add some water flow resistance. Moreover, elbows should turn in a straight direction, not in a horizontal direction, to avoid collecting air.

During the installation of the pipeline, the horizontal section should be level or slightly upward.

This action allows air to accumulate within the intake pipe, reducing the vacuum level in the下降水管 and pump, which in turn lowers the pump's water lift and decreases the output flow. The proper approach is: the horizontal section should be slightly inclined towards the water source, not level, and certainly not arched upwards.

Five: The multi-stage centrifugal pump's inlet is directly connected to the elbow.

This can cause uneven distribution of water flow as it enters the impeller through the elbow. When the diameter of the inlet pipe is larger than the pump's inlet, a reducer pipe should be installed. Some reducer pipes should be mounted flatly, while others should be mounted at an angle. Otherwise, air pockets may form, reducing water output or preventing water from being pumped, along with noises such as impacts. If the diameter of the inlet pipe is the same as the pump's inlet, a straight pipe should be added between the pump's inlet and the elbow, with the length of the straight pipe not less than 2 to 3 times the diameter of the pipe.

Six, the outlet of the multistage centrifugal pump is above the normal water level of the discharge pool.

If the outlet is above the normal water level of the pond, even with the added pump head, the flow rate has been reduced. If the terrain conditions necessitate that the outlet be higher than the pond's water level, a bend and a short pipe should be installed at the pipe opening to transform the water pipe into a siphon, thereby lowering the outlet height.

Section 7: Incorrect orientation of the water inlet of the inlet pipe

① The inlet opening of the water intake pipe is less than the diameter of the opening from the bottom and side walls of the intake pool. If there are sediments or dirt at the bottom of the pool, when the distance from the intake opening to the bottom is less than 1.5 times the diameter, it may cause inadequate water intake or the suction of sediments and debris during pumping, blocking the intake opening.

② If the water intake depth of the inlet pipe is insufficient, it can cause whirlpools around the water surface of the intake pipe, affecting water intake and reducing flow 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.

When setting the bottom valve, the lowest section of the inlet pipe is not straight.

As installed, the valve cannot seal itself, leading to leaks. The correct method is to ensure that the lowest section of the inlet pipe with the bottom valve is straight. If the terrain conditions prevent a straight installation, the angle between the water pipe axis and the horizontal plane should be above 60°. Zibo Jieyou Pump Co., Ltd. specializes in the following main products:Stainless Steel Submersible Pump，Deep Well Submersible PumpSubmersible axial flow pumps, submersible sewage pumps, and various vacuum pumps, vacuum pump units, submersible axial flow pumps, axial flow pumps, mixed flow pumps, semi-open impeller pumps, slurry pumps, centrifugal pumps, pipeline pumps, chemical industry pumps, self-priming pumps, submersible pumps, deep well pumps, sewage pumps, desulfurization pumps, diaphragm pumps, magnetic pumps, screw pumps, fluoroplastic pumps, engineering plastic pumps, and other products.