Failure Analysis of Centrifugal Pump

Centrifugal pump is a pump that relies on the centrifugal force generated when the impeller rotates to transport liquid. What causes the centrifugal pump to fail to deliver water? Here are the failure analyses.

  1. Horizontal Centrifugal PumpSome users do not fill enough water before the pump is started. Sometimes it seems that the water filled has overflowed from the vent hole, but the pump shaft is not rotated and the air is completely discharged, causing a little air to remain in the inlet pipe or pump body.
  2. The downward gradient of 0.5% or more shall be applied to the reverse flow direction of the horizontal section of the inlet pipe contacting the centrifugal pump. The end connected to the inlet of the centrifugal pump is the highest, not completely horizontal. If it is tilted upwards, air will be trapped in the water inlet pipe. This reduces the vacuum in the water pipe and the centrifugal pump and affects water absorption.
  3. The packing of the centrifugal pump has worn out due to long-term use, or because the packing is too loose, causing a large amount of water to spray out from the gap between the packing and the shaft sleeve of the pump. As a result, external air enters the interior of the centrifugal pump from these gaps and affects the lifting of water.
  4. Due to long-term potential underwater, the inlet pipe has holes in the wall corrosion. After the pump worked, the water surface kept dropping. When these holes are exposed to the surface of the water, air enters the inlet pipe from the holes.
  5. If there are cracks in the elbow of the inlet pipe, and there is a tiny gap between the inlet pipe and the centrifugal pump, it may cause air to enter the inlet pipe.
  6. Too much suction. Some water sources are deep, and some water sources have a relatively flat periphery, ignoring the allowable suction stroke of the pump, resulting in little or no water absorption. It is necessary to know that the degree of vacuum that can be established at the suction port of the water pump is limited. The suction range in absolute vacuum is about 10 meters water column height, and it is impossible for a water pump to establish an absolute vacuum. Moreover, if the vacuum is too large, it is easy to vaporize the water in the pump, which is not good for the pump. Therefore, each centrifugal pump has its maximum allowable suction stroke, which is generally between 3 and 8.5 meters. When installing a water pump, you must not just covet convenience and simplicity.
  7. The resistance loss in the water inlet and outlet pipes is too large. Some users have found through measurement that although the vertical distance from the reservoir or water tower to the water surface is slightly smaller than the pump lift, the amount of water lifted is still small or unable to lift the water. The reason is often that the pipe is too long, the water pipe has many bends, and the resistance loss of the water flow in the pipe is too large. In general, a 90-degree elbow has greater resistance than a 120-degree elbow. The head loss of each 90-degree elbow is about 0.5 to 1 meter, and the resistance of every 20 meters of pipe can make the head loss about 1 meter. In addition, some users also arbitrarily arrange the pipe diameters of the water pump inlet and outlet pipes, which also have a certain impact on the head.
  8. The pump speed is too low.
  • Human factors. A considerable part of the users, due to the damage of the original motor, will be driven by another motor at will. As a result, the flow rate is low, the head is low, or even the water cannot be pumped.
  • Wear of the transmission belt. Many large-scale water separation pumps use belt transmission. Due to long-term use, the transmission belt wears and changes and slips, which reduces the speed of the pump.
  • Improper installation. The center distance between the two pulleys is too small or the two shafts are not too parallel; the tight side of the transmission belt is installed on it; the wrap angle is too small; errors in the calculation of the diameter of the two pulleys and the large eccentricity of the two shafts of the coupling drive will cause the change of the pump speed.
  • Mechanical failure of the centrifugal pump itself. The fastening nut between the impeller and the pump shaft is loose or the pump shaft is deformed and bent, causing the impeller to move too much, directly rubbing against the pump body, or the bearing is damaged. These may reduce the speed of the pump.
  • Power machine maintenance is not recorded. The motor loses its magnetism due to burnt windings. Changes in the number of winding turns, wire diameters, and wiring methods during maintenance, or failure to completely eliminate factors during maintenance can also change the pump speed.

Other factors

  • The bottom valve cannot be opened. It is usually caused by the fact that the bottom valve gasket is stuck due to the long time that the pump has been stored. A bottom valve without a gasket may rust to death.
  • The filter screen of the bottom valve is clogged, or the bottom valve is potentially in the sludge layer in the water, causing the block of the filtering net.
  • The impeller is severely worn. The impeller blades wear out after long-term use, which affects the pump performance.
  • The failure or blockage of the gate valve or check valve will cause the flow to decrease or even fail to pump water.
  • Leakage of the outlet pipe will also affect the amount of water lifted.
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