All machinery inevitably encounters issues, particularly water pumps, which see heavy daily use. Pump malfunctions can range from reduced water flow to a complete stoppage of supply, causing significant inconvenience to our daily lives and work. However, the mechanical structure of common water pumps is relatively simple and stable, making it feasible for us to perform our own inspections and troubleshoot common faults. Learning to troubleshoot and repair pumps yourself can reduce downtime and allow for the timely restoration of the water supply. Today, the pump experts at Shanghai Shenyin Pump Manufacturing Co., Ltd. will briefly explain how to troubleshoot and repair common pump malfunctions.
1. Pump is seized: Check by manually rotating the coupling; if necessary, disassemble the pump to identify and resolve issues between the rotating and stationary parts.
2. Pump fails to discharge liquid: Insufficient priming (or air not fully vented from the pump). Solution: Re-prime the pump;
Incorrect rotation direction. Solution: Check the direction of rotation;
Pump speed too low. Solution: Check the speed and increase it;
Strainer clogged or foot valve malfunctioning. Solution: Check the strainer and remove debris;
Suction lift too high or vacuum forming in the suction tank. Solution: Reduce suction lift; check pressure in the suction tank.
3. Pump discharge interrupted: Air leak in the suction pipeline. Solution: Check suction-side pipe connections and the condition of the stuffing box seal;
Air not fully vented during priming. Solution: Re-prime the pump;
Suction side suddenly blocked by foreign matter. Solution: Stop the pump and remove the obstruction;
Large amount of gas/air sucked in. Solution: Check for vortices at the suction inlet and ensure the submergence depth is sufficient.
4. Insufficient flow rate: System static head increased. Solution: Check liquid level and system pressure;
Increased resistance loss. Solution: Check for obstructions in the pipeline, check-valves, etc.;
Excessive wear on the casing and impeller wear rings. Solution: Replace or repair the wear rings and impeller;
Leakage from other parts. Remedy: Inspect components such as the shaft seal.
Pump impeller clogged, worn, or corroded. Remedy: Clean, inspect, or replace.
5. Insufficient head—causes and remedies: Impeller installed backwards (double-suction impeller). Remedy: Inspect the impeller; liquid density or viscosity does not match design specifications. Remedy: Check the physical properties of the liquid;
Excessive flow rate during operation. Remedy: Reduce the flow rate.
6. Pump vibration or abnormal noise—causes and remedies: Vibration frequency is 0–40% of the operating speed. Excessive bearing clearance, loose bearing shells, impurities in the oil, poor oil quality (viscosity, temperature), oil foaming due to air or process fluid, poor lubrication, or damaged bearings. Remedy: Inspect and take appropriate measures, such as adjusting bearing clearance, removing impurities from the oil, or replacing the oil;
Vibration frequency is 60%–100% of the operating speed; causes include excessive seal clearance, loose retaining rings, or seal wear. Remedy: Inspect, adjust, or replace the seal. Vibration frequency is twice the operating speed; causes include misalignment, loose coupling, friction in the sealing assembly, casing deformation, bearing damage, support resonance, thrust bearing damage, shaft bending, or poor fit. Remedy: Inspect and take appropriate measures to repair, adjust, or replace components. Vibration frequency is *n* times the operating speed; causes include pressure pulsation, misalignment, casing deformation, seal friction, resonance in the support or foundation, or resonance in piping/machinery. Remedy: Reinforce the foundation or piping. Vibration frequency is very high; causes include shaft friction, seal or bearing issues, lack of precision, bearing instability, or poor shrink fit.
7. Causes and remedies for bearing overheating: Bearing pads scraped/fitted incorrectly. Remedy: Refinish or replace the bearing pads.
Bearing clearance is too small. Remedy: Readjust clearance or scrape/fit the bearing;
Insufficient or poor-quality lubricating oil. Remedy: Increase oil quantity or replace the lubricant;
Improper bearing assembly. Remedy: Inspect assembly against specifications and rectify non-compliant factors;
Cooling water supply interrupted. Remedy: Inspect and repair;
Bearing wear or looseness. Remedy: Repair or scrap the bearing.
Looseness (tighten relevant bolts); bent pump shaft. Remedy: Straighten the pump shaft;
Deformed oil thrower ring (unable to rotate or lift oil). Remedy: Replace the oil thrower ring;
Poor coupling alignment or insufficient axial clearance. Remedy: Check alignment and adjust axial clearance.
8. Shaft seal overheating—causes and remedies: Packing compressed too tightly or causing friction. Remedy: Loosen packing and inspect the water seal pipe;
Misalignment between the water seal ring and water seal pipe. Remedy: Re-check and align;
Poor flushing or cooling. Remedy: Inspect the flushing and cooling circulation piping;
Mechanical seal malfunction. The remedy is to inspect the mechanical seal.
9. Causes and remedies for excessive rotor axial movement (end play) include: improper operation and operating conditions that deviate significantly from the pump's design parameters.
Remedy: Ensure strict adherence to operating procedures so that the pump consistently operates near its design conditions;
Obstructed balancing system. Remedy: Clear the balance line;
The material of the balance disc and balance disc seat does not meet specifications.
Remedy: Replace the balance disc and balance disc seat with components made of materials that meet specifications.
We hope this guide on troubleshooting and repairing water pump malfunctions proves helpful to you.