Sea Water Pump Impeller Balancing on a Cargo Vessel

The Challenge

A 42,000 DWT bulk carrier docked at Ambarlı port in Turkey reported excessive vibration on the starboard auxiliary sea water pump. The centrifugal pump drives cooling water to the main engine heat exchangers at 1,750 RPM. After 8,000 running hours, cavitation pitting on the bronze impeller had shifted its mass distribution. Drive-end bearing vibration reached 11.6 mm/s RMS — deep into ISO 10816 Zone D (danger).

The chief engineer had already ordered a replacement impeller, but delivery was 10 days out. The vessel was scheduled to depart in 36 hours. Running the pump in its current state risked a bearing seizure mid-voyage. A shore-based vibration consultant brought Balanset-1A aboard.

What Happened

The pump was isolated from the sea chest and run on a closed test loop. A vibration sensor was clamped to the drive-end bearing housing with a magnetic base. The tachometer was aimed at a reflective strip on the coupling.

Baseline measurement confirmed 11.6 mm/s at 1× RPM — pure imbalance. A 12 g trial weight was attached to one of the impeller’s back-shroud bolt holes using marine-grade stainless hardware. After the trial run, Balanset-1A calculated a correction of 8.5 g at 195°.

The correction weight was drilled from a stainless steel blank and secured with Loctite. Final vibration: 1.3 mm/s RMS, comfortably in Zone A.

Why It Matters

The entire procedure took 30 minutes, performed in the engine room while cargo operations continued on deck. No port delay, no schedule change, no emergency spare parts. The vessel departed on time with both auxiliary pumps operational.

The chief engineer noted that previous bearing replacements on this pump had occurred every 4,000 hours. With the vibration now at 1.3 mm/s, the estimated bearing life extends to over 12,000 hours — a 3× improvement that pays for the Balanset-1A unit in a single application.