Thread Content
Centrifugal water pumps are one of the most widely used types of pumps in agriculture due to their simple structure, ease of use and maintenance, and high efficiency. However, they can be quite troublesome as they sometimes fail to lift water. Now, an analysis will be conducted on the reasons for this intentional obstruction of water supply. There is air in the water inlet pipe and inside the pump (1) Some users fail to fill the pump with enough water before starting it ； 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, leaving 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 water pump’s inlet should be at the highest point and not completely horizontal. If it tilts upward, 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, causing a large amount of water to spray out from the gap between the packing and the pump shaft sleeve. As a result, 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 bends 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 take over its function; as a result, this leads to low flow rates, low head pressure, or even an inability to pump water. (2) Wear of the conveyor belt. Many large-scale water pump exchangers use belts for transmission; over time, the belts wear out and become loose, resulting in slippage and thus a decrease in the pump’s 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 rotation 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 significantly and come into direct contact with the pump casing; or it can lead to damage to the bearings, all of which may reduce the speed of the water pump. (5) Repair of power engines is not recorded. The motor loses its magnetism due to burned-out windings, and changes in the number of winding turns, wire diameter, or wiring method during repair, or factors such as unresolved faults during repair can also cause the pump speed to change. 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 in 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 under vacuum is approximately 10 meters of water column, and it is not possible for a pump to create such a high level of vacuum. Moreover, an excessive vacuum level can easily cause the water inside the pump to vaporize, which is detrimental to the operation of the pump. Therefore, each centrifugal pump has its own maximum allowable suction head, 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. Some users, after conducting measurements, find that even though the vertical distance from the reservoir or water tower to the water surface is 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 pipeline is too long and has many bends, resulting in excessive flow resistance loss within the pipeline. The reason is often that the pipeline is too long and has many bends, resulting in excessive flow resistance loss within the pipeline. 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 can 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 pipeline leading out of Lü also affect the water lift capacity.