DHB

Establish baseline vibration measurements at bearing housings in three axes (horizontal, vertical, axial) when pump is new or after overhaul. During operation, any vibration increase of 25% from baseline indicates developing problems such as imbalance, misalignment, bearing wear, or cavitation. Audible rattle or noticeable heat at bearing indicates imminent failure.

Monitor seal flush flow rate and temperature daily on critical cooling pumps. Any drop in flush flow rate or rise in temperature signals impending seal failure. Visual check: pronounced seepage from weep hole indicates seal degradation. Replace seals at manufacturer-recommended intervals (typically 2-4 years for marine duty) rather than waiting for visible leakage.

For seawater cooling applications: inspect pump casing, impeller, and shaft for graphitic corrosion (iron matrix corrodes while graphite skeleton remains, leaving structurally weak component). Verify material specification: for seawater duty, only accept bronze, aluminium bronze, or duplex stainless steel casings/impellers. Cast iron casings fail rapidly in seawater service.

Compare operating discharge pressure and flow rate against manufacturer performance curves. Unexplained drops in pressure or flow indicate cavitation, impeller erosion, or internal blockage. Listen for cavitation noise (like gravel in pump). Verify NPSH (net positive suction head) at suction flange meets or exceeds pump requirement. High temperature rise (>10°C above inlet) indicates cavitation or excessive wear.

Inspect flexible coupling (CNL, DHB series) for excessive wear, cracking, or deterioration. Check motor-pump alignment using laser alignment tool; parallel and angular misalignment both contribute to bearing failure and vibration. For rigidly coupled designs (QVK, QH), verify no axial or radial movement at coupling interface. Inspect all bolts for correct torque.