After ruining dozens of water pumps, I finally figured out the pattern of their failures!-Hezhong Environment (Beijing) Co., Ltd. was established in 2003

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After ruining dozens of water pumps, I finally figured out the pattern of their failures!

Published Time:

2022-07-15

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During operation, potential pump malfunctions can be predicted by observing or monitoring the pump's flow rate, sound, vibration, temperature, current, electrical protection device tripping, and controller alarms. Wastewater treatment plants should predict malfunctions through various methods based on their operating conditions: using flow rate, sound, vibration, and temperature as basic malfunction prediction methods; plants with the capability can further predict malfunctions based on current, electrical protection device tripping, and controller alarms.

Pump malfunction prediction and handling should follow the principle of prediction first, then on-site confirmation, and then processing.

1. Flow Rate Prediction

1. Significant Flow Rate Reduction

If the pump flow rate significantly decreases (more than 20% below the normal value), the following items should be checked one by one, and corresponding measures should be taken.

a) Outlet pipe valve is not open or is blocked: Open the valve or clear the pipe.
b) Suction head is excessive: Lower the pump's installation height or replace it with a pump with a larger suction head.
c) Suction pipe or foot valve leaks: Repair or replace the suction pipe or foot valve.
d) Insufficient submergence depth of the foot valve: The submergence depth of the foot valve should be greater than 1.5 times the diameter of the inlet pipe. Increase the water depth if insufficient.
e) Cavitation or erosion perforation of the volute: Replace the volute.
f) Impeller blockage or wear of the sealing ring: Clear the blocked impeller or replace the worn impeller sealing ring.
g) Wear or detachment of the wear ring at the inlet: Replace the wear ring if wear exceeds the specifications; reinstall the detached wear ring.
h) Severe corrosion of the pump shaft, bearings, and leakage rings: Replace severely corroded components.
i) Incorrect impeller rotation: Adjust the motor wiring.
j) Motor shaft rubbing: Replace the bearings or motor.
k) Check valve malfunction in parallel pumps: Replace the check valve.

2. Zero Flow Rate

1. Check if the power is on; reconnect if not.

2. Check if the relay and contactor are functioning properly; replace the damaged relay or contactor if not. If the power is normal but the pump cannot restart, move the pump to the maintenance area and check the following items one by one, and take corresponding measures.

a) Packing is too tight or impeller is blocked: Loosen the packing or clear the inlet channel.
b) Impeller, bearings, or leakage rings are stuck or rusted: Disassemble the pump body to remove debris or rust.
c) Pump shaft is bent: Remove the pump shaft for correction or replacement.
d) Waterproof cable is damaged: Cut the damaged section of the cable and reconnect or replace the damaged cable.
e) Poor sealing or waterproofing at the power cord connection: Reseal after repairing or replacing the affected inlet components.
f) Mechanical seal is severely worn: Replace the mechanical seal after repairing or replacing the affected inlet components.
g) O-ring is severely worn: Replace the O-ring after repairing or replacing the affected inlet components.
h) Bolts at the seal are not tightened: Retighten the bolts after repairing or replacing the affected inlet components.
i) Motor insulation resistance is too low: If 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) Three-phase power wiring fault in three-phase pumps: Check and reconnect as follows: 1) Check for poor cable contact; 2) Check for missing phases in the power supply and motor; 3) Check the balance of three-phase voltage and current.

3. If the power is normal and the pump can restart, but there is still no flow, move the pump to the maintenance area and check the following items one by one, and take corresponding measures.

a) Pump body and suction pipe are not filled with the conveying medium: Eliminate foot valve malfunction and fill the conveying medium.
b) Dynamic water level is below the pump inlet pipe: Lower the pump's installation position or raise the dynamic water level; restart the pump after the dynamic water level is above the inlet pipe.
c) Suction pipe is cracked: Repair or replace the suction pipe.
d) Check valve malfunction in parallel pumps: Replace the check valve.

2. Sound Prediction

If there is noise or unusual sound during pump operation, move the pump to the maintenance area and check the following items one by one, and take corresponding measures.

a) Motor ball bearings are damaged or stuck: Replace the motor ball bearings.
b) Pump bearings are damaged or impeller is jammed: Replace the bearings or clear foreign objects from the impeller.
c) Pump shaft is bent or not concentric/parallel with the motor shaft: Straighten the bent pump shaft or adjust the relative position of the pump and motor.
d) Installation is loose or pump is installed too high: Adjust the pump or lower its installation height.
e) Inlet well level is too low: Adjust the inlet level.
f) Suction port is blocked: Clear foreign objects from the pump suction port.

3. Vibration Prediction

1. The main causes of abnormal pump vibration are mechanical and hydraulic.

2. Mechanical causes can be checked item by item as follows, and corresponding measures can be taken.

a) Foreign objects stuck in the pump impeller or shaft bearing: Remove the foreign objects.
b) Uneven mass distribution of the pump impeller or motor rotor: Replace the impeller or motor.
c) Misalignment between the pump shaft and motor shaft: Adjust the pump shaft and motor shaft to be concentric.
d) Non-conforming bolt spacing of the coupling: Adjust the gap between the couplings.
e) Main shaft speed is close to the critical speed: Adjust the main shaft speed.
f) The pump main shaft is bent, and the rotating parts touch the bushing and bearing, causing the pump shaft to deflect: Replace the abnormal parts.
g) The base is not firm or the bolts are not tightened: Strengthen the base and tighten the bolts.
h) The vibration frequency of the water pump is close to the vibration frequency of the pipe, resulting in resonance: The pipe can be reinforced.

3. Hydraulic causes can be checked item by item as follows, and corresponding measures can be taken.

a) Cavitation causes vibration: A high-suction pump can be replaced.
b) Water impact on the tongue and the leading edge of the guide vane causes vibration: Adjust the distance between the impeller outlet and the pump volute tongue or the leading edge of the guide vane.
c) Water well level is too low or the pump suction inlet is blocked: Adjust the water intake level or clear the pump suction inlet of foreign objects.
d) Surging phenomenon: Handle according to the pump's instructions.

4. Temperature Prediction

If the pump body temperature is too high, check item by item as follows, and take corresponding measures.

a) Bearing wear or jamming: Add lubricant or replace the bearing.
b) Bearing or motor overload: Reduce operating power or replace a higher-power water pump.
c) Lack of conveying medium: Ensure that the valves before and after the pump body are open to ensure sufficient conveying medium height.

5. Current Prediction

When the current is abnormal, the pump should be moved to the maintenance area, and the following items should be checked and corresponding measures taken.

a) Abnormal operating conditions: Verify the on-site operating conditions and replace or adjust facilities that do not meet the operating conditions.
b) Bearing abnormality: Inspect, repair, or replace the bearing.
c) Speed exceeds rated speed: Check the circuit voltage and reduce the pump speed.
d) Coupling misalignment or pump shaft bending: Correct or replace the pump shaft.
e) Obstruction by debris: Clear the debris.
f) Motor ball bearing damage: Replace the motor ball bearing.
g) Improper use of water pump head: Replace the water pump with a suitable head.

6. Electrical Protection Component Trip Prediction

1. Electrical protection component trips include thermal relay protection action trips, air switch protection action trips, and AC contactor protection action trips.

2. If the thermal relay protection action trips, check item by item as follows, and take corresponding measures.

a) Poor thermal relay contact: Replace the thermal relay.
b) Current setting value is too small: Increase the current setting value.
c) Overload operation: Reduce operating power; if the fault cannot be eliminated, the motor should be replaced.
d) Impeller blockage or jamming: Clear the intake channel.
e) Three-phase motor single-phasing operation: Rewire or replace the motor.
f) Winding temperature control cable is damaged or broken: Replace the damaged part.

3. If the air switch protection action trips, check item by item as follows, and take corresponding measures.

a) Air switch selection does not match the load: Replace the air switch.

b) Soft starter or inverter failure: Replace the damaged part.

c) Short circuit in the power line: Rewire.

d) Short circuit between phases, turns, or to ground in the motor winding: Replace the motor.

e) Pump overload operation: Reduce operating power; if the fault cannot be eliminated, the motor should be replaced.

4. If the AC contactor protection action trips, check item by item as follows, and take corresponding measures.

a) AC contactor coil failure: Replace the AC contactor coil.

b) AC contactor auxiliary contact abnormality: Adjust or replace the AC contactor auxiliary contact.

c) Intermediate relay abnormality: Replace the intermediate relay.

d) Short circuit between phases, turns, or to ground in the motor winding: Replace the motor.

7. Controller Alarm Prediction

1. Oil Chamber Leakage Alarm

If the controller leakage alarm is triggered, check item by item as follows, and take corresponding measures.

a) False signal: Press the reset button.
b) Sensor abnormality: Disconnect the wires, check the sensor, and replace the faulty part.
c) Water ingress into the cooling oil chamber: Drain and clean the cooling oil chamber, and replace the sealing parts.
d) Pump body or base perforation: Replace the pump.

2. Bearing Temperature Alarm

If the bearing temperature alarm is triggered, please check the following items one by one and take corresponding measures.

a) False signal: Press the reset button.
b) Pump controller malfunction: Press the reset button. If it cannot be restored, open the box to check the controller and replace the faulty part.
c) Sensor malfunction: Replace the sensor.
d) Bearing displacement or damage: Move the pump to the maintenance area to check the bearing. If the bearing is faulty, repair or replace the faulty bearing.

3. Motor winding alarm

If the motor winding alarm is triggered, please check the following items one by one and take corresponding measures.

a) False signal: Press the reset button.
b) Temperature control switch circuit is open: Close the circuit.
c) Motor overload: Reduce the motor operating frequency or close the outlet valve. If the fault cannot be eliminated, replace the motor.
d) Motor insulation resistance or inter-phase/inter-turn insulation abnormality: Replace the motor.
e) Winding temperature control cable is damaged or broken: Replace the damaged part.
f) Three-phase motor is working with a missing phase: Reconnect the wires