Analysis of common faults of centrifugal pump and daily maintenance

1 Structure and working principle of centrifugal pump 1.1 structure of centrifugal pump the structure of centrifugal pump can be basically divided into horizontal centrifugal pump and vertical centrifugal pump according to the position of shaft, and can be divided into volute type and guide vane type according to the type of press out chamber and suction mode Centrifugal pump is composed of four parts: prime mover, impeller, pump shell and shaft seal device The prime mover is the power device of centrifugal pump, which is generally connected with the pump body through coupling transmission or other transmission methods to provide kinetic energy; there are generally 6-12 backward curved blades in the impeller, whose main function is to transmit the mechanical energy of the prime mover to the delivered liquid; the pump casing, also known as the volute, is an energy conversion device that collects the liquid thrown out by the impeller; the shaft seal device is the pump shaft Seal to pump housing Its function is to prevent high-pressure liquid from leaking out of the pump housing along the circumference of the shaft or outside air to enter the pump housing inward 1.2 working principle of centrifugal pump Take the common water pump as an example Before starting, the pump shell should be filled with liquid first After starting, the impeller rotates at a high speed driven by the motor When the impeller rotates, the pressure of water at the inlet of the impeller decreases, which is lower than the atmospheric pressure, while the pressure of water along the radius of the impeller keeps rising, which is far higher than the atmospheric pressure In this way, a certain suction is formed in the water inlet pipe Under the external atmospheric pressure, the water at the lower part pushes the water inlet valve, enters the pump shell along the water inlet pipe, and is thrown in and out of the water pipe by the impeller In this way, the water in the lower part can be continuously pumped to the higher part [3] 2 Common faults and repair suggestions of centrifugal pump: there are various reasons for the faults of centrifugal pump, including inherent faults of equipment, installation faults, operation faults and model selection errors For example, the pump can not be started normally, the pump does not discharge water or the flow is insufficient, the pump vibration and noise, the bearing heating, the pump overpower, cavitation, etc [4] When judging the fault of centrifugal pump, we should combine the basic index of equipment state and rich maintenance experience to diagnose Here are some common faults 2.1 starting fault 2.1.1 motor fails to start normally If the motor is used as the original device, first move the cooling fan of the motor by hand to see whether it can rotate flexibly: if it is flexible, it may be that the starting capacitance is invalid or the capacity is reduced, when the starting capacitance of the same value is replaced; if it does not rotate, it means that the rotor is stuck, when the rust is cleaned, add lubricating grease, or remove the foreign matters of the stuck rotor 2.1.2 reverse rotation of water pump: in case of this kind of situation, it often occurs in * times of use, the machine shall be shut down immediately If it is a motor, any two phases in the three-phase power supply shall be replaced to change the rotation direction of the water pump If the diesel engine is used as the power, the connection mode of the belt shall be considered 2.1.3 centrifugal pump does not discharge water after rotation If the rotation is normal but the water does not come out, the possible causes are: 1) the suction port is blocked by sundries, and the filter device should be installed after removal; 2) the suction pipe or instrument leaks, which may leak from the weld, the pipe has sand holes or cracks, the gasket at the joint is poorly sealed, etc.; 3) the suction height is too high, which should be reduced; 4) the impeller has cavitation; 5) the water injected into the pump is not enough; 6) there is air in the pump, which should be discharged The empty method is to close the pump outlet regulating valve and open the circuit valve; 7) the water outlet resistance is too large, the length of the water pipe should be checked or the water outlet pipe should be cleaned; 8) the water pump speed is not enough, the water pump speed should be increased 2.2 operation fault 2.2.1 insufficient flow or stop Possible reasons are: 1) impeller or water inlet and outlet pipes are blocked, impeller or pipeline shall be cleaned; 2) sealing ring and impeller are seriously worn, and damaged sealing ring or impeller shall be replaced; 3) pump shaft speed is lower than the specified value, and pump speed shall be adjusted to the specified value; 4) bottom valve opening degree is not enough or check valve is blocked, bottom valve shall be opened or stop to clean check valve; 5) water suction pipe submergence depth is not enough To make the pump absorb air; 6) the suction pipe leaks air; 7) the packing leaks air; 8) the sealing ring is worn, the new sealing ring shall be replaced or the impeller shall be turned round, and the thickened sealing ring shall be equipped; 9) the impeller is severely worn; 10) the sand content in the water is too large, the filtering facilities shall be added or the startup shall be avoided 2.2.2 in case of abnormal sound or excessive vibration, the whole unit shall be stable and sound shall be normal during normal operation of water pump If there is noise or abnormal vibration in the unit, it is often the precursor of pump failure, and the unit shall be shut down for inspection immediately to eliminate the hidden danger The reason of pump unit vibration is very complex From the cause of vibration, it mainly includes mechanical, hydraulic, electrical and other aspects From the mechanism of vibration, it mainly includes excessive vibration force, insufficient rigidity, resonance and so on The possible causes are: 1) the impeller balance is not calibrated, which should be corrected immediately; 2) the pump shaft is not concentric with the motor shaft, which should be corrected; 3) the foundation is not solid, the arm support is not firm, or the anchor bolt is loose; 4) the rotation of the pump or motor rotor is unbalanced     Hydraulic aspects: 1) the suction head is too large, and cavitation occurs at the impeller inlet; when the water flows through the impeller, bubbles appear in the low-pressure area, and the bubbles collapse in the high-pressure area, resulting in impact and vibration, at this time, the installation height of the pump should be reduced; 2) the pump operates at non design points, and the flow is too large or too small, which will cause the pressure change or pressure pulsation of the pump; 3) the pump inhales foreign matters, blocks or damages the impeller, which should be Shut down for cleaning 4) When several pumps are running in parallel, the intake pipe is arranged improperly, and the vortex causes the suction condition of the pump to deteriorate The vibration caused by resonance is mainly caused when the natural frequency of the rotor is consistent with the speed of the water pump Therefore, corresponding measures shall be taken to solve the above fault causes after making a judgment 2.2.3 Bearing Overheating During operation, if the bearing is hot, the causes shall be investigated and handled from the following aspects: 1) insufficient lubricating oil or poor oil circulation; 2) poor quality of lubricating oil and impurities make the bearing rusty, worn and inflexible; 3) serious bearing wear; 4) different center between pump and motor; 5) too loose or too tight fit between bearing inner ring and pump shaft journal; 6) too tight belt when driving with belt ; 7) if the axial thrust is too large, the balance hole on each impeller shall be dredged [3,5,6] 2.2.4 excessive power consumption of pump If the ammeter reading is abnormal and the motor is heated during the operation of the pump, it may be caused by the over power operation of the pump The possible causes are as follows: 1) friction occurs in the rotating part of the pump, such as impeller and sealing ring, impeller and shell; 2) the rotation speed of the pump is too high; 3) the specific gravity or viscosity of the delivered liquid exceeds the design value; 4) the packing is too tight or the packing box is not filled with water; 5) the bearing is worn or damaged ; 6) the shaft is bent or deviated; 7) the pump runs at a large flow rate with deviation from the design point 3 Daily maintenance of centrifugal pump 3.1 precautions for use of centrifugal pump 3.1.1 preparation before startup In order to ensure the safe operation of the water pump, necessary inspection shall be done before starting the machine: first, turn the coupling or pulley slowly by hand, observe whether the water pump is turning correctly, whether the rotation is flexible and stable, whether there are sundries in the pump, whether the bearing is running normally, whether the belt is tightened properly; check whether all screws are firm; check whether there are sundries around the unit that hinder the operation; check the submergence depth of the water suction pipe Check whether the temperature is enough; close the outlet valve to reduce the starting load, and open the valve in time after starting 3.1.2 during operation, after startup, check whether all instruments work normally and stably, and the current shall not exceed the rated value The pointer of the pressure gauge shall be within the design scope; check whether the water output of the water pump is normal, and check whether all parts of the unit are leaking; check the compaction degree of the packing Generally, there should be a small amount of leakage at the packing (no more than 10-20 drops per minute), and the leakage of the mechanical seal should not be greater than 10ml / h (about 3 drops per minute); the temperature of the rolling bearing should not be higher than 75 ℃; the temperature of the sliding bearing should not be higher than 75 ℃ It should be higher than 70 ℃ And pay attention to whether there is abnormal noise, abnormal vibration and water output reduction; timely adjust the submergence depth of the water inlet pipe mouth; frequently clean the floating objects on the trash rack; pay attention to whether the belt slips if it is driven by the belt 3.1.3 shutdown and precautions after shutdown Before the shutdown, the outlet valve shall be closed before the shutdown to prevent water backflow and damage to the parts; after each shutdown, the oil stains on the pump body and pipeline shall be wiped out in time to keep the appearance of the unit clean and hidden dangers shall be found in time; after the shutdown in winter, the water shall be drained out immediately to prevent freezing and cracking of the pump body and internal parts; after the end of the use season, necessary maintenance shall be carried out [7] 3.2 periodic inspection of centrifugal pump The periodic inspection of centrifugal pump can be generally divided into the following three types: 1) daily inspection, i.e inspection in use, as described above; 2) monthly inspection, cleaning and minor repair of equipment surface without dismantling parts, including inspection of bearing temperature, shaft seal leakage reason and motor edge; 3) regular maintenance Including replacing the shaft seal lubricating oil, checking the alignment of the pump and motor, checking the wear of the shaft sleeve, checking the damage of the rubber ring of the coupling, cleaning the mechanical seal, coolant filter and pump filter, checking the wear of the sliding parts, checking the damage and corrosion of the parts contacting the liquid [8] 4 the conclusion is only a brief summary of the common faults and troubleshooting methods in the actual use of centrifugal pump, and provides precautions in the daily use of centrifugal pump, hoping to provide practical convenience for everyone [print this page], [return], [Close] Disassembly and assembly method of mechanical seal of centrifugal pump 2009-11-4 working principle of submersible pump 2009-9-12