Faults and troubleshooting of centrifugal pumps

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Centrifugal pumps are prone to the following faults, with the causes and solutions as follows: 1. The pump fails to start or experiences high starting load. ① The prime mover or power supply is abnormal. The solution is to check the power supply and the prime mover. ②The pump is stuck. The handling method is to manually rotate the coupling for inspection; if necessary, disassemble it for inspection in order to eliminate faults in the moving and stationary parts. ③The filler is pressed too tightly. The solution is to loosen the filler. ④The discharge valve is not closed. The solution is to close the discharge valve and restart. ⑤The balance tube is not unobstructed. The solution is to clear the balance tube. 2. The pump does not discharge liquid: ① Insufficient priming (or gas remaining inside the pump). The solution is to refill the pump. ②The pump is turned in the wrong direction. The solution is to check the rotation direction. ③The pump speed is too low. The solution is to check the speed and increase it. ④The filter screen is clogged, and the bottom valve is not functioning properly. The solution is to check the filter screen and remove any debris. ⑤The suction height is too high, or a vacuum has formed in the liquid suction tank. The solution is to reduce the suction height ； Check the suction tank pressure. 3. Interruption after the pump discharges fluid: ① Air leakage in the suction line. The solution is to check the connections of the suction side pipes as well as the sealing condition of the stuffing box. ②The gas on the suction side was not completely exhausted during pump filling. The solution is to request a re-pumping. ③The inhalation side was suddenly blocked by a foreign object. The solution is to stop the pump in order to remove the foreign object. ④Inhale a large amount of gas. The solution is to check whether there are vortices at the suction inlet and whether the submersion depth is too shallow. 4. Insufficient traffic ①, same as 2 and 3. The solution is to take appropriate measures. ②The system’s static head increases. The solution is to check the liquid level and system pressure. ③, the resistance loss increases. The solution is to check for obstructions such as pipes and check valves. ④The casing and the wear rings of the impeller are excessively worn. The solution is to replace or repair the wear ring and impeller. ⑤Leakage in other areas. The solution is to check areas such as the shaft seal. ⑥Clogging, wear, and corrosion of the pump impeller. The treatment methods are cleaning, inspection, and replacement. 5. Insufficient head: ① Same as 2’s ①, ②, ③, ④; 3’s ①; 4’s ⑥. The solution is to take appropriate measures. ②, the impeller is installed in reverse (double-suction impeller). The solution is to check the impeller. ③The liquid density and viscosity do not match the design conditions. The treatment method is to check the physical properties of the liquid. ④The flow rate is too high during operation. The solution is to reduce the traffic. 6. High power consumption during operation: ① Friction between the impeller and the wear-resistant ring, as well as between the impeller and the casing. The solution is to check and repair it. ②, same as item ④ of 5. The solution is to reduce the traffic. ③The liquid density increases. The solution is to check the liquid density. ④The filler is pressed too tightly or there is dry friction. The solution is to loosen the packing and check the water seal tube. ⑤The bearing is damaged. The solution is to inspect, repair, or replace the bearing. ⑥The rotation speed is too high. The solution is to check the drive and power supply. ⑦The pump shaft is bent. The solution is to correct the pump shaft. ⑧The axial force balance mechanism failed. The solution is to check the balance hole and whether the return water pipe is blocked. ⑨Poor coupling alignment or too small an axial clearance. The solution is to check the alignment and adjust the axial clearance. 7. Pump vibration or abnormal noises: ①, ③ from 3, ⑤, ⑦, and ⑨ from 6. The solution is to take appropriate measures. ②The vibration frequency ranges from 0 to 40% of the operating speed. Excessively large bearing clearance, loose bearing shells, impurities in the oil, poor oil quality (viscosity, temperature), foaming of the oil due to air or process fluids, inadequate lubrication, and damaged bearings. The solution involves conducting inspections and taking appropriate actions, such as adjusting the bearing clearance, removing impurities from the oil, and replacing it with fresh oil. ③The vibration frequency is 60% to 100% of the operating speed. Regarding bearing issues, it is the same as in (2): either the sealing gap is too large, the retainer is loose, or the seal is worn out. The solution is to inspect, adjust, or replace the seal. ④The vibration frequency is twice the operating speed. Misalignment, loose couplings, friction in the sealing devices, deformation of the housing, damaged bearings, support resonance, damaged thrust bearings, bent shafts, poor fit. The approach is to conduct inspections, take appropriate measures, and repair, adjust, or replace as necessary. ⑤The vibration frequency is n times the operating speed. Pressure pulsations, misalignment, shell deformation, seal friction, resonance in supports or foundations, resonance in pipelines or machinery – the treatment methods are the same as those in (4): reinforce the foundation or pipelines. ⑥The vibration frequency is very high. Shaft friction, sealing issues, bearings, lack of precision, bearing vibration, poor fit due to shrinkage, etc. The handling method is the same as ④. 8. Bearing overheating ①. The bearing shells were not lapped to the required standard. The solution is to repair the bearing shells again or replace them. ②The bearing clearance is too small. The solution is to readjust the bearing clearance or perform scraping. ③Insufficient amount of lubricating oil, poor quality of the oil. The solution is to increase the oil amount or replace the lubricant. ④The bearings are poorly assembled. The solution is to check the bearing assembly as required and eliminate any factors that do not meet the specifications. ⑤Cooling water circuit broken. The treatment method is inspection and repair. ⑥Bearing wear or looseness. The solution is to repair the bearing or discard it. Wasmatsu Kyō, retighten the relevant bolts. ⑦The pump shaft is bent. The solution is to correct the pump shaft. ⑧The oil slinger is deformed; it cannot rotate and thus cannot transfer oil. The solution is to replace the oil slinger. ⑨Poor coupling alignment or too small an axial clearance. The solution is to check the alignment and adjust the axial clearance. 9. Shaft seal overheating ①: The packing is too tight or there is friction. The solution is to loosen the packing and check the water seal tube. ②The water seal ring and the water seal tube are out of alignment. The solution is to recheck the alignment. ③Rinsing, cooling are good. The solution is to check the flushing and cooling circulation pipe. ④The mechanical seal is faulty. The solution is to check the mechanical seal. 10. Large rotor play ①: Improper operation, with operating conditions far from the pump’s designed conditions. Solution: Operate strictly to keep the pump running near its designed operating conditions at all times. ②The balance is not smooth. The solution is to clear the balance tube. ③The material of the balance disc and its holder does not meet the requirements. The solution is to replace the balance disc and its holder with materials that meet the requirements. 11. Water hammer occurs①: A sudden power outage leads to fluctuations in system pressure, resulting in negative pressure in the discharge system; bubbles dissolved in the liquid escape, causing gas to accumulate within the pump or pipes. The solution is to vent the gas completely. ②The high-pressure liquid column rushed back rapidly due to a sudden power outage, striking the valve plate of the check valve at the pump outlet. The solution is to modify the layout of the pipes in the pump’s unreasonable discharge system as well as the pipe fittings. ③The valve of the outlet pipeline was closed too quickly. The method of handling this is to slowly close the valve.