Centrifugal pump is widely used in agriculture because of its simple structure, convenient use and maintenance, and high efficiency. However, it is also troublesome because it can not lift water sometimes. This paper analyzes the reasons for the failure to raise the level of water.

There is air in the inlet pipe and pump body

(1) Some users did not fill up enough water before the pump was started; sometimes it seemed that the filled water had overflowed from the vent hole, but the pump shaft was not rotated to discharge the air completely, resulting in a little air remaining in the water inlet pipe or pump body. (2) The horizontal section of the water inlet pipe in contact with the water pump should have a downward slope of more than 0.5% against the water flow direction, and the end connecting the water pump inlet should be Zui high, not completely horizontal. If it is tilted upward, air will be left in the water inlet pipe, which will reduce the vacuum degree in the water pipe and water pump and affect the water absorption.

(3) The packing of the pump has been worn or the packing is too loose due to long-term use, resulting in a large amount of water ejected from the gap between the packing and the shaft sleeve of the pump. As a result, the external air enters the interior of the pump from these gaps, affecting the water lifting.

(4) Because of the long-term potential underwater, there are holes in the pipe wall corrosion of the inlet pipe. After the pump works, the water surface continues to drop. When these holes come out of the water surface, air enters the inlet pipe through the holes.

(5) The crack at the elbow of the water inlet pipe and the small gap between the water inlet pipe and the water pump may cause air to enter the water inlet pipe

Pump speed too low

(1) Human factors. Due to the damage of the original motor, quite a number of users randomly equipped with another motor to drive. As a result, the flow rate is low, the head is low and even the water can not be pumped.

(2) The drive belt is worn. There are many large-scale water pump from the belt, because of long-term use, the transmission belt is worn and loose, there is a slip phenomenon, thus reducing the speed of the pump.

(3) Improper installation. If the center distance between the two pulleys is too small or the two shafts are not parallel, the tight edge of the drive belt is installed on it, the wrap angle is too small, the calculation error of the diameter of the two pulleys and the large eccentricity of the two shafts of the coupling drive water pump will cause the change of the pump speed.

(4) Mechanical failure of water pump itself. Loose fastening nut of impeller and pump shaft or deformation and bending of pump shaft cause impeller to move more, directly rub with pump body, or bearing damage, which may reduce the speed of water pump.

(5) Power machine maintenance is not recorded. The motor loses its excitation due to the burning of its winding. The change of winding turns, wire diameter and wiring method in the maintenance, or the failure is not completely eliminated in the maintenance, will also change the speed of the water pump.

The suction range is too large

Some of the water sources are deeper, and some of them are flat on the periphery, but the allowable suction head of the pump is ignored, resulting in little or no water absorption at all. It is necessary to know that the vacuum degree that can be established at the suction port of the pump is limited. The suction head under vacuum is about 10 m water column high, and the vacuum that cannot be established by the pump. Moreover, if the vacuum is too large, it is easy to make the water in the pump gasified, which is not conducive to the work of the pump. Therefore, each centrifugal pump has its own large allowable suction head, which is generally between 3 and 8.5 meters. When installing the pump, it is necessary to make the drawing convenient and simple.

The resistance loss in the inlet and outlet pipes of water flow is too large

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 less than the lift of the pump, the water is still small or can not be lifted. The reason is that the pipeline is too long and there are many bends in the pipe, and the resistance loss of water flow in the pipeline is too large. The reason is that the pipeline is too long and there are many bends in the pipe, and the resistance loss of water flow in the pipeline is too large. In general, the resistance of 90 degree bend is greater than that of 120 degree elbow, and the head loss of each 90 degree elbow is about 0.5-1 m, and the head loss of every 20 m pipe is about 1 m. In addition, some users also randomly pump in and out of the pipe diameter, which also has a certain impact on the lift.

Influence of other factors

(1) The bottom valve cannot be opened. Usually due to the pump shelving time is too long, the bottom valve gasket is stuck, no gasket bottom valve may rust.

(2) The filter net of bottom valve is blocked; or the filter screen is blocked in the sludge layer of bottom valve potential water.

(3) The impeller is seriously worn. The wear of impeller blade after long-term use affects the performance of water pump.

(4) Failure or blockage of gate valve or check valve will cause flow reduction or even failure to pump water.

(5) Leakage in the outlet pipe will also affect the water withdrawal.