Pump

Bearings and coupling

Rolling-element bearings support the shaft and are lubricated by grease or, on larger pumps, a shared oil system; a flexible coupling connects the pump to its prime mover and tolerates the small residual misalignment that even a carefully aligned installation retains.

Prime mover

Most ship's pumps are electric-motor driven; some essential pumps such as emergency bilge or fire pumps have a diesel-driven or otherwise independent prime mover specifically so they remain available after a loss of the main electrical supply.

Selection and sizing

Regulations and class

SOLAS and class rules require duplication or independent backup for essential pumping services, including bilge, fire, cooling water and fuel transfer, so that a single pump failure does not remove the function entirely. The emergency bilge pump and fire pump requirements under SOLAS Chapter II-1 and II-2 call for a source of power independent of the main engine room in many ship types, which is why these particular pumps are diesel-driven or supplied from the emergency switchboard rather than sharing the main pump room's electrical feed.

Typical faults

• Cavitation from insufficient NPSH - pitted impeller vanes, noise, falling flow, often from a partially blocked suction strainer or a suction lift that has grown since commissioning.
• Mechanical seal failure - leakage at the shaft, usually from dry running, misalignment, or a flushing line blocked or shut for other work and not reopened.
• Bearing failure from misalignment - heat and vibration at the bearing housing, traceable to coupling wear or a foundation that has settled.
• Air lock in a centrifugal pump - loss of prime and no flow despite the pump running, common after maintenance that opened the suction line.
• Excessive internal clearance wear on positive-displacement types - falling delivered flow at the same speed, reducing fuel injection consistency or transfer rate without an obvious external symptom.

What to look for in a supplier

• Wear parts and mechanical seal kits specific to the pump model, since seal faces and elastomer compatibility vary by liquid service.
• Documented performance curves so a replacement or repaired pump can be checked against its original duty point, not just against similar ratings.
• Materials matched to the actual liquid handled, particularly for seawater service where the wrong alloy shortens service life significantly.

When a centrifugal pump loses flow, check for an air lock or blocked strainer before assuming impeller wear - most sudden flow loss on these pumps is a priming or suction problem, not a worn part.