Class 2 (2nd Engineer) MEP 📅 Oct 2022

Exam Question

(a) Describe, with the aid of sketches, a turbocharger bearing lubrication system, stating the type of bearing employed and explaining the advantages and disadvantages of the lubricating system described.

(b) One of the main engine turbocharger on the vessel aboard which you are serving as Second Engineer has suffered a sudden and unexpected failure. Explain the incident and give a reasoned proposed action to be undertaken to bring the turbocharger back into service.

Reference Answer

The turbocharger employs a self-contained lubrication system utilizing ball and roller bearings. The bearings are housed within a casing, the bottom of which acts as an oil sump. A gear pump, driven directly by the turbine shaft, draws oil from this sump and delivers a pressurized jet of oil directly to the bearings. Both the turbine and blower sides utilize this identical system. A sight glass allows for oil level monitoring, while drain and fill plugs facilitate maintenance. This design is typically found in axial flow turbochargers.
The blower side employs a double-row ball bearing to accommodate axial thrust loads and axially locate the turbocharger rotor assembly. The turbine side utilizes a single-row ball bearing, allowing for thermal expansion of the rotor shaft. Leaf springs are incorporated between the outer race of the bearings and the housing to dampen vibrations and reduce bearing chatter, extending bearing life.
Advantages of the Lubrication System
The gear pump-driven system ensures better lubrication at increased speeds.

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