Centrifugal Pump Blockage: Causes, Diagnosis & Step-by-Step Fix

Five Early Warning Signs

1. Flow falls while the pump sounds normal — the suction strainer is slowly plugging.
2. Discharge pressure drops — the impeller inlet or vane passages are partially blocked.
3. Motor current rises above nameplate — the pump is working against a restricted passage.
4. Periodic surging — a large object is being drawn against the impeller then released.
5. Overheating at the stuffing box — reduced flush flow through a clogged seal line.

Safe Clearance Procedure

• Isolate: close suction and discharge valves; lock out the starter.
• Drain the casing and disconnect the coupling.
• Remove the casing cover and inspect the impeller inlet for rags, stones or scale.
• Clean the strainer and flush the suction line back into the sump.
• Check wear rings; replace if clearance is more than double the new value.
• Reassemble, vent, and restart against a closed valve, opening slowly.