Q: - Compressed air starting system for ocean going ships has specific requirements with particular importance being assigned to requirement for air compressor. Pl enumerate these requirements, with reasons as relevant. `
10. Two or more compressors shall be installed with a total capacity sufficient for charging the air receivers from atmospheric to full pressure in the course of one (1) hour.
ANSWER :-
1. In every ship means shall be provided to prevent overpressure in any part of compressed air systems and wherever water jackets or casings of air compressors and coolers might be subjected to dangerous overpressure due to leakage into them from air pressure parts. Suitable pressure relief arrangements shall be provided for all systems.
2. The main starting air arrangements for main propulsion internal combustion engines shall be adequately protected against the effects of backfiring and internal explosion in the starting air pipes.
3. All discharge pipes from starting air compressors shall lead directly to the starting air receivers, and all starting pipes from the air receivers to main or auxiliary engines shall be entirely separate from the compressor discharge pipe system.
4. Provision shall be made to reduce to a minimum the entry of oil into the air pressure systems and to drain these systems.
5. Air intakes for the compressors shall be so located as to minimise the intake of oil or water contaminated air.
6. Pipes from air compressors with automatic start shall be fitted with a separator or similar device to prevent condensate from draining into the compressors.
7. Starting systems for internal combustion engines shall have capacity for a number of starts specified without reloading of air receivers.
The capacity shall be divided between at least two air receivers of approximately same size .
8. If a starting system serves two or more of the above specified purposes, the capacity of the system shall be the sum of the capacity requirements.
9. For multi-engine propulsion plants the capacity of the starting air receivers shall be sufficient for 3 starts per engine. However, the total capacity shall not be less than 12 starts and need not exceed 18 starts.
11.The capacity shall be approximately equally shared between the compressors. At least one of the compressors shall be independently driven.
12.If the emergency generator is arranged for pneumatic starting, the air supply shall be from a separate air receiver.
13.The emergency starting air receiver shall not be connected to other pneumatic systems, except for the starting system in the engine room. If such a connection is arranged, then the pipeline shall be provided with a screw-down non-return valve in the emergency generator room.
For Survey requirements
1. All air receivers and other pressure vessels for essential services together with their mountings and safety devices are to be cleaned internally and examined internally and externally. If an internal examination of an air receiver is not practicable it is to be tested hydraulically to 1.3 times the working pressure.
2. Air compressors are to be opened up and coolers tested as considered necessary by the Surveyor. Selected pipes in the starting air systems are to be removed for internal examination and hammer tested. If an appreciable amount of lubricating oil is found in the pipes the starting air system is to be thoroughly cleaned by steaming or other suitable means. Some of the pipes selected are to be those adjacent to the starting air valves at the cylinders and to the discharges from the air compressors
