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The reason why centrifugal pump cannot lift water
The centrifugal pump is the most widely used pump in agriculture because of its simple structure, convenient use and maintenance, and high efficiency, but it is annoying because it sometimes fails to pump water. Here are some reasons that you need to know.
Air in intake pipe and pump body

(1) Some users do not fill enough water before the pump is started; sometimes it seems that the filled water has overflowed from the vent hole, but the air is completely discharged without rotating the pump shaft, which causing a little air to remain in the water inlet pipe or pump body .
(2) Apply a descending slope of more than 0.5% to the horizontal section of the inlet pipe in contact with the pump. The end connected to the pump inlet is the highest, not completely horizontal. If it is tilted upward, air will remain in the water inlet pipe, which reduces the vacuum in the water pipe and the pump, and affects water absorption.
(3) The packing of the water pump has been worn out for a long time or the packing is too loosely pressed, causing a large amount of water to be ejected from the gap between the packing and the shaft sleeve of the pump. Affecting water extraction.
(4) The inlet wall of the inlet pipe is corroded due to the long-term underwater, and the water surface continues to decline after the pump works. When these holes are exposed, the air enters the inlet pipe from the hole.
(5) Cracks appear at the bend of the inlet pipe, and there is a slight gap at the connection between the inlet pipe and the pump, which may cause air to enter the inlet pipe.

Pump speed is too low
(1) Human factors. A considerable number of users are randomly equipped with another motor to drive because the original motor is damaged. As a result, low flow, low head and even no water.
(2) The belt is worn. There are many large-scale centrifugal water pumps that use belt transmission. Due to long-term use, the transmission belt wears and loosens and slips, which reduces the speed of the pump.
(3) Improper installation. If the center distance of the two pulleys is too small or the two shafts are not parallel, the tight edge of the transmission belt is installed on the top, resulting in a too small wrap angle. Changes in pump speed.
(4) The mechanical failure of the pump itself. The loosening of the fastening nuts of the impeller and the pump shaft or the deformation and bending of the pump shaft cause the impeller to move more, directly rub against the pump body, or damage the bearings, which may reduce the speed of the pump.
(5) Power machine maintenance is not recorded. The motor is demagnetized due to the burning of the winding. Changes in the number of winding turns, wire diameter, wiring method during maintenance, or failure to completely eliminate the factors during maintenance will also change the speed of the pump.

Suction is too large
Some water sources are deeper, and some water sources have flatter peripheral terrain, ignoring the allowable suction head of the pump, resulting in little or no water absorption. It is necessary to know that the vacuum degree that can be established at the suction port of the pump is limited. The suction range under absolute vacuum is about 10 meters of water column height, and it is impossible for the pump to establish an absolute vacuum. And the vacuum is too large, it is easy to make the water in the pump vaporized, which is unfavorable for the pump. Therefore, each centrifugal pump has its maximum allowable suction head, which is generally between 3 and 8.5 meters. When installing the pump, it is necessary to be simple and convenient.
Excessive resistance loss in the water inlet and outlet pipes
Some users have measured that although the vertical distance from the reservoir or water tower to the water surface of the water source is slightly smaller than the pump head, it still has a small amount of water or no water. The reason is often that the pipeline is too long, there are many bends in the water pipe, and the resistance loss of water flow in the pipe is too large. The reason is often that the pipeline is too long, there are many bends in the water pipe, and the resistance loss of the water flow in the pipe is too large. Under normal circumstances, 90-degree elbows have greater resistance than 120-degree elbows. Each 90-degree elbow has a head loss of about 0.5 to 1 meter, and the resistance of each 20-meter pipe can cause a head loss of about 1 meter. In addition, some users also freely choose the diameter of the pump inlet and outlet pipes, which also have a certain impact on the head.

Influence of other factors
(1) The bottom valve cannot be opened. Usually the pump is left for too long, the bottom valve gasket is stuck, and the bottom valve without gasket may be rusted.
(2) The filter screen of the bottom valve is blocked; or the filter screen is blocked in the potential sludge layer in the bottom valve.
(3) The impeller is badly worn. Impeller blades wear out after long-term use, which affects the performance of the pump.
(4) The fault or blockage of the gate valve or check valve will cause the flow rate to decrease or even fail to pump water.
(5) Leakage of the outlet pipe will also affect the capacity of water delivery.