Auxiliary Machinery and Systems
Core concepts
Expect questions on boilers (auxiliary and exhaust gas economiser), feed water treatment and testing, steam traps and condensate systems, air compressors and receivers, fresh water generators, oily water separators, purifiers, refrigeration and air conditioning, steering gear, and ballast/bilge systems. Understand safety valves, gauge glasses, water level controls, and the statutory testing of pressure vessels. Know pump types (centrifugal, positive displacement, gear, screw) and their priming and cavitation characteristics.
Traps
- Confusing boiler water tests: alkalinity, chloride, phosphate, hydrazine and dissolved oxygen have different limits and treatments.
- Forgetting that an exhaust gas economiser must be kept circulating when the engine runs, even at low load, to avoid dry running and soot fire.
- Mixing up purifier bowl assembly and gravity disc selection; wrong disc gives poor separation or water carry-over.
- Assuming a centrifugal pump is self-priming; it is not.
- Overlooking that air receiver safety valves and relief devices have statutory test intervals.
Worked example / rule of thumb
Rule of thumb: boiler chloride limit for shell boilers is typically 200–300 mg/L; exceeding it risks carry-over and priming. For air compressors, the receiver should be drained at least daily, and the safety valve tested at intervals set by the classification society. Always use the maker's manual and the ship's planned maintenance system as the authority.