Patterns of pump failures

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During operation, potential pump failures can be predicted by observing or monitoring aspects such as the pump’s flow rate, sound, vibration, temperature, current, tripping of electrical protection devices, and controller alarms. The fault prediction and handling for pumps should follow the principle of predicting first, confirming on-site second, and then taking action. 1. Flow prediction 1. Significant drop in flow: If the pump’s flow rate decreases significantly (by more than 20% below the normal value), the following checks should be carried out one by one, and appropriate measures taken. a) The valve on the pump discharge pipe is not open or is blocked: The valve can be opened or the pipe can be cleared. b) The pump’s suction height is too high: Lower the pump’s installation height or replace it with a pump that has a greater suction range. c) Air leakage in the suction pipe and bottom valve: Repair or replace the suction pipe and bottom valve. d) Insufficient submersion depth of the bottom valve: The submersion depth of the bottom valve should be greater than 1.5 times the diameter of the water inlet pipe; if it is insufficient, the depth of water immersion should be increased. e) Volute cavitation or erosion perforation: Replace the volute. f) Impeller blockage or wear of the seal ring: Clear any blockages in the impeller or replace the worn impeller seal ring. g) Wear or detachment of the wear ring at the water inlet: The wear ring should be replaced if the wear exceeds the requirements specified in the manual; if it has detached, it must be reinstalled. h) Severe corrosion of pump shaft, bearings, and leakage prevention rings: Replace the severely corroded components. i) Incorrect impeller rotation: Adjust the motor wiring. j) Motor stator rubbing: Replace the bearings or the motor. k) Failure of the parallel pump check valve: Replace the check valve. 2. No data flow. 1. Check whether the power supply is connected; if not, reconnect it. 2. Check whether the relays and contactors can operate properly. If they cannot, replace the damaged relays or contactors. When the power supply is normal but the pump cannot be restarted, the pump should be moved to the maintenance area, and the issues should be checked one by one as follows, with appropriate measures taken. a) Excessively tight packing or clogged impeller: Loosen the packing or clear the water inlet channel. b) Impeller, bearings, and leakage prevention rings are stuck or rusted: Disassemble the pump body to remove debris or perform rust removal. c) Bent pump shaft: Remove the pump shaft for straightening or replace it. d) Damaged waterproof cable: Cut out the damaged section of the cable and reconnect it, or replace the damaged cable. e) Poor sealing or waterproofing at the power cable connections: After repairing or replacing the components affected by water ingress, reseal them. f) Severe wear of the mechanical seal: Replace the mechanical seal after repairing or replacing the components affected by water ingress. g) Severe wear of the O-ring: Replace the O-ring after repairing or replacing the components affected by water ingress. h) Bolts at the seal are not tightened: After repairing or replacing the components affected by water ingress, retighten the bolts. i) Excessively low insulation resistance of the motor: When the insulation resistance does not meet the requirements, dry the motor, re-immerse it in insulating paint, rewind the motor coils, or replace the motor. j) Faults in the three-phase power wiring of a three-phase pump: Inspection and rewiring can be carried out as follows: 1) Check whether the cables have poor connections ； 2) Check whether the power supply and motor are missing a phase ； 3) Check the balance of voltage and current across the three phases of the power supply. 3. If the power supply is normal and the pump can be restarted but no flow is still present, the pump should be moved to the maintenance area for thorough inspection of each component as outlined below, and appropriate actions should be taken. a) The pump body and suction pipe are not filled with the conveying medium: Fix the bottom valve issue and fill the conveying medium. b) The operating water level is below the pump’s inlet pipe: Lower the pump’s installation height or raise the operating water level, and then start the pump once the operating water level is above the inlet pipe. c) Broken suction pipe: Repair or replace the suction pipe. d) Fault in the check valve of the parallel pump: Replace the check valve. 2. Sound prediction: In the event of noise or abnormal sounds during pump operation, the pump should be moved to the maintenance area where it can be inspected item by item as follows, and appropriate measures should be taken. a) Damaged or stuck motor ball bearings: Replace the motor ball bearings. b) Damaged pump bearings or stuck impeller: Replace the bearings or clean out any debris from the impeller. c) The pump shaft is bent, or it is not aligned or parallel to the motor shaft: Correct the bent pump shaft or adjust the relative position of the pump and the motor. d) Poor installation or the water pump being installed too high: Adjust the water pump or lower its installation height. e) Inlet well water level is too low: Adjust the inlet water level. f) Suction port blockage: Clear foreign objects from the pump’s suction port. 3. Vibration prediction 1. The main causes of abnormal pump body vibration can be divided into mechanical and hydraulic factors. 2. Mechanical causes can be checked item by item as follows, and corresponding measures can be taken. a) Foreign objects are stuck in the pump impeller or bearings: Remove the foreign objects. b) The mass distribution of the pump impeller or motor rotor is uneven: the impeller or motor should be replaced. c) Deviation between the pump shaft and the motor shaft: Align the pump shaft and the motor shaft to be concentric. d) The bolt spacing of the coupling is unacceptable: Adjust the gap between the couplings. e) The spindle speed is close to the critical speed: Adjust the spindle speed. f) The pump shaft is bent; the rotating part comes into contact with the bushing and bearing shells, causing the pump shaft to deflect: Replace the defective components. g) The base is not sturdy or the bolts are not tight: Reinforce the base and the bolts. h) Resonance occurs when the vibration frequency of the water pump is close to that of the pipeline: the pipeline can be reinforced. 3. Hydraulic causes can be checked item by item as follows, and corresponding measures can be taken. a) Cavitation-induced vibration: A pump with a higher suction lift can be used. b) Vibration caused by water flow hitting the baffle and the leading edge of the guide vanes: Adjust the distance between the impeller outlet and the baffle of the pump volute or the leading edge of the guide vanes. c) Excessively low water level in the well or blockage at the pump inlet: Adjust the water level or remove any foreign objects blocking the pump inlet. d) Surge phenomenon: Handle it in accordance with the pump’s manual instructions. 4. Temperature prediction: If the pump temperature is too high, conduct checks according to the items listed below and take appropriate measures. a) Bearing wear or jamming: Add lubricant or replace the bearing. b) Bearing or motor overload: Reduce the operating power or replace it with a pump of higher power. c) Lack of conveying medium: Ensure the valves before and after the pump are open to maintain an adequate level of the conveying medium. 5. Current prediction: When there is an abnormal current, the pump should be moved to the maintenance area, and inspections should be carried out step by step as follows, with appropriate measures taken. a) Abnormal operating conditions: Verify the on-site operating conditions, and replace or adjust facilities that do not meet these conditions. b) Bearing abnormality: Inspect, repair, or replace the bearing. c) Rotational speed exceeds the rated speed: Check the circuit voltage and reduce the pump speed. d) The coupling is out of alignment or the pump shaft is bent: Correct or replace the pump shaft. e) Obstruction by debris: Clear the debris. f) Damaged motor ball bearings: Replace the motor’s ball bearings. g) Improper selection of the water pump head: Replace it with a pump having an appropriate head. 6. Prediction of tripping of electrical protection components
1. Tripping of electrical protection components includes tripping due to the operation of thermal relays, air circuit breakers, and AC contactors. 2. If the thermal relay trips due to protection activation, conduct inspections step by step as follows and take corresponding measures. a) Poor contacts of the thermal relay: Replace the thermal relay. b) The current setting value is too low: increase the current setting value. c) Overload operation: Reduce the operating power; if the fault cannot be resolved, the motor should be replaced. d) Impeller is clogged or jammed: Clear the water guide groove. e) Operation of a three-phase motor with a missing phase: Reconnect the wiring or replace the motor. f) Damage or breakage of the winding temperature control cable: Replace the damaged component. 3. If the air circuit breaker trips due to protection activation, conduct inspections step by step as follows and take appropriate measures. a) The air switch selected is not compatible with the load: Replace the air switch. b) Soft starter or inverter failure: Replace the damaged components. c) Short circuit in the power circuit: Reconnect the wires. d) There are short circuits between phases, between turns, and to ground in the motor windings: Replace the motor. e) Pump operating under overload: Reduce the operating power; if the fault cannot be resolved, the motor should be replaced. 4. If the AC contactor trips due to protective action, the following steps can be taken for troubleshooting one by one, along with corresponding measures. a) AC contactor coil malfunction: Replace the AC contactor coil. b) Abnormality of the auxiliary contacts of the AC contactor: Adjust or replace the auxiliary contacts of the AC contactor. c) Abnormal intermediate relay: Replace the intermediate relay. d) There are short circuits between phases, between turns, and to ground in the motor windings: Replace the motor. 7. Predictive alarm handling for the controller
1. Oil chamber leak alarm
If the controller triggers a leak alarm, the following steps can be taken one by one to troubleshoot and implement appropriate measures. a) Fake signal: Press the reset button. b) Sensor abnormality: Disconnect wires, inspect the sensor, and replace any defective parts. c) Water inlet to the cooling oil chamber: Drain and clean the cooling oil chamber, and replace the sealing components. d) Perforation in the pump body and base: Replace the pump. 2. Bearing temperature alarm: If a bearing temperature alarm is triggered, check each item as follows and take corresponding measures. a) Fake signal: Press the reset button. b) Pump controller malfunction: Press the reset button; if it does not work, open the unit to inspect the controller and replace the faulty component. c) Sensor abnormality: Replace the sensor. d) Faults such as bearing displacement or damage: The pump should be moved to a maintenance area to inspect the bearings; if there is a fault with the bearings, they should be repaired or replaced. 3. Motor winding alarm: If there is an alarm related to the motor windings, it is possible to troubleshoot step by step as follows and take appropriate measures. a) False signals: The reset button should be pressed. b) Temperature control switch circuit open: Close the circuit. c) Motor overload: Reduce the motor operating frequency or close the outlet valve slightly; if the fault cannot be resolved, the motor should be replaced. d) Abnormal motor insulation resistance or inter-phase/inter-turn insulation: Replace the motor. e) Damage or breakage of the winding temperature control cable: Replace the damaged component. f) Operation of a three-phase motor with one phase missing: Reconnect.