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Why can’t a centrifugal water pump lift water? Analysis of the causes of failure. Centrifugal water pumps are among the most widely used types in agriculture due to their simple structure, ease of use and maintenance, and high efficiency. However, they can be quite troublesome when they fail to lift water. Now, an analysis will be conducted on the causes of this water supply failure. There is air in the inlet pipe and inside the pump (1) Some pumps do not have enough water filled in them before they are started ； Sometimes it seems that the water poured in has overflowed through the vent holes, but the pump shaft was not rotated to completely expel the air, resulting in some air remaining in the inlet pipe or within the pump body. (2) The horizontal section of the inlet pipe in contact with the water pump should have a slope of more than 0.5% in the direction opposite to the flow of water; the end connected to the pump’s inlet should be at the highest point, and it should not be completely horizontal. If it curls upwards, air will remain in the water inlet pipe, reducing the vacuum level in the pipe and pump and affecting water suction. (3) The packing of the water pump has worn out due to long-term use, or it is too loose, resulting in a large amount of water spraying out from the gap between the packing and the pump shaft sleeve. As a consequence, external air enters the interior of the water pump through these gaps, affecting its ability to lift water. (4) Due to being submerged underwater for a long time, the pipe walls of the water inlet pipe corroded and developed holes; as the water level dropped continuously after the pump started operating, air entered the water inlet pipe through these holes once they came above the water surface. (5) Cracks at the bend of the water inlet pipe, as well as slight gaps at the connection between the water inlet pipe and the water pump, can both allow air to enter the water inlet pipe. The water pump speed is too low. (1) Human factors. A considerable number of users, due to the damage of the original motor, simply install another motor to drive the pump, which results in low flow rates, low head pressure, or even an inability to draw water. (2) Wear of the drive belt. Many large-scale water pump exchangers use belt drives; over time, the belts wear out and become loose, resulting in slippage and thus a decrease in the pump’s rotational speed. (3) Improper installation. A too small center distance between the two pulleys, or axes that are not parallel enough, result in the tight side of the drive belt being installed on top, which leads to a too small wrap angle. Errors in calculating the diameters of the pulleys, as well as a large eccentricity between the axes of a pump driven by a coupling, can all cause changes in the pump’s rotational speed. (4) Mechanical failures of the water pump itself. Loose fastening nuts on the impeller and pump shaft, or deformation and bending of the pump shaft, can cause the impeller to shift outward and come into direct contact with the pump body; or damage to the bearings can also lead to a reduction in the pump’s speed. (5) Power unit maintenance is not recorded. The motor loses its magnetism due to burned-out windings, and changes in the number of windings turns, wire diameter, or wiring method during repair, or factors such as incomplete elimination of faults during repair, can also cause a change in the pump’s speed. The suction lift is too high; some water sources are deep, while in other cases the area surrounding the water source is relatively flat. This leads to neglect of the allowable suction lift for the pump, resulting in less water being drawn in or no water being drawn at all. It should be understood that there is a limit to the degree of vacuum that can be created at the water intake of a pump; the suction height achievable at absolute vacuum is approximately 10 meters of water column, and it is impossible for a pump to create an absolute vacuum. Moreover, an excessive vacuum level can easily cause the water inside the pump to vaporize, which is detrimental to the operation of the water pump. Therefore, each centrifugal pump has its maximum allowable suction lift, which is generally between 3 and 8.5 meters; when installing a water pump, one must not prioritize convenience and simplicity. The resistance loss in the inlet and outlet pipes for water flow is too high. In some cases, despite the vertical distance from the reservoir or water tower to the water surface being slightly less than the pumping head of the water pump, the amount of water pumped is low or no water can be pumped at all. The reason is often that the pipes are too long and have many bends, resulting in excessive flow resistance loss within the pipes. The reason is often that the pipes are too long and have many bends, resulting in excessive flow resistance loss within the pipes. Under normal circumstances, a 90-degree elbow creates more resistance than a 120-degree elbow; each 90-degree elbow results in a head loss of about 0.5 to 1 meter, while the resistance over every 20 meters of pipe can cause a head loss of around 1 meter. Furthermore, some users arbitrarily choose the diameters of the water inlet and outlet pipes, which also has a certain impact on the head pressure. Impact of other factors: (1) The bottom valve cannot be opened. It is usually because the water pump has been left unused for too long, causing the gasket of the bottom valve to stick; a bottom valve without a gasket may also rust. (2) The bottom valve filter screen is clogged ； Or the bottom valve may cause clogging of the filter screen in the underlying layer of sludge in the water. (3) The impeller is severely worn. The impeller blades wear out over time, affecting the performance of the water pump. (4) Malfunctions or blockages in the gate valve or check valve can result in reduced flow rate or even prevent water from being pumped. (5) Leaks in the outlet pipeline can also affect the water lift capacity. This post was last edited by Maybe it was a dream on 2008-1-25 06:56.]