Analysis Of The Reasons Why Sanitary Centrifugal Pumps Cannot Lift Water

Sanitary Centrifugal Pump has become the most widely used water pump in agriculture due to its simple structure, convenient use and maintenance, and high efficiency, but it is also annoying because it sometimes cannot lift water.
1. There is air in the water inlet pipe and pump body
1. Some users do not fill the water pump with enough water before starting it. Sometimes it seems that the water has overflowed from the vent hole, but the pump shaft is not turned to completely discharge the air, resulting in a small amount of air remaining in the water inlet pipe or pump body.
2. The horizontal section of the water inlet pipe in contact with the self-priming centrifugal oil pump should have a downward slope of more than 0.5% against the direction of the water flow, and the end connected to the water pump inlet should be the highest. Do not be completely horizontal. If it is tilted upward, air will remain in the water inlet pipe, reducing the vacuum in the water pipe and the water pump, affecting water absorption.
3. The packing of the self-priming pump has been worn out due to long-term use or the packing is pressed 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 from these gaps, affecting water lifting.
4. The water inlet pipe has been submerged underwater for a long time, and the pipe wall has holes due to corrosion. After the water pump is working, the water level continues to drop. When these holes are exposed to the water surface, air enters the water inlet pipe from the holes.
5. Cracks appear at the bend of the water inlet pipe, and there is a small gap at the connection between the water inlet pipe and the water pump, which may allow air to enter the water inlet pipe.

The speed of the water pump is too low
1. Human factors. A considerable number of users arbitrarily match another motor to drive the original motor due to damage, resulting in small flow, low head or even no water supply.
2. Drive belt wear. Many large centrifugal pumps use belt transmission. Due to long-term use, the drive belt wears and loosens, resulting in slippage, thereby reducing the speed of the water pump.
3. Improper installation. The center distance between the two pulleys is too small or the two shafts are not parallel, the drive belt is installed too tightly on it, resulting in a small wrap angle, errors in the calculation of the diameters of the two pulleys, and the large eccentricity of the two shafts of the coupling drive water pump, which will cause changes in the speed of the water pump.
4. Mechanical failure of the self-priming pump itself. The impeller and pump shaft fastening nut is loose or the pump shaft is deformed and bent, causing the impeller to move more, directly rubbing against the pump body, or bearing damage, which may reduce the speed of the water pump.
5. The power machine is not properly maintained. The motor loses magnetism due to winding burnout. Changes in the number of winding turns, wire diameter, and wiring method during maintenance, or factors that fail to completely eliminate the fault during maintenance will also change the speed of the water pump.

2. The suction range is too large
Some water sources are deeper, and the outer terrain of some water sources is relatively flat, but the allowable suction range of the water pump is ignored, resulting in less water suction or no water suction at all. It should be known that the vacuum that can be established at the water inlet of the water pump is limited. The suction range of absolute vacuum is about 10 meters of water column height, and the water pump cannot establish an absolute vacuum. Moreover, if the vacuum is too large, it is easy to vaporize the water in the pump, which is not conducive to the operation of the water pump. Therefore, each centrifugal pump has its maximum allowable suction range, which is generally between 3-8.5 meters.
Some users have measured that although the vertical distance from the reservoir or water tower to the water surface is slightly less than the pump head, the water volume is still small or no water can be lifted. 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 pipeline 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 water flow in the pipeline is too large. Under normal circumstances, the resistance of a 90-degree elbow is greater than that of a 120-degree elbow. The head loss of each 90-degree elbow is about 0.5-1 meter, and the resistance of each 20-meter pipeline can cause a head loss of about 1 meter. In addition, some users also arbitrarily adjust the diameter of the inlet and outlet pipes of the water pump, which also has a certain impact on the head.

3. Influence of other factors
1. The bottom valve cannot be opened. Usually, it is because the water pump has been shelved for too long, the bottom valve gasket is stuck, and the bottom valve without a gasket may rust.
2. The filter net of the bottom valve is blocked; or the filter net is blocked by the sludge layer in the water of the bottom valve.
3. The impeller is seriously worn. The impeller blades are worn after long-term use, affecting the performance of the water pump.
4. Faults or blockages in the gate valve or check valve will cause a decrease in flow or even no water can be pumped.
5. Leakage in the outlet pipe will also affect the water lifting capacity of the self-priming pump.