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Which requirements apply to the starting and control air system?

15 Jun '17, 23:36

June 15, 2017, 11:36 p.m.
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System design requirements

Most of the engines used in marine industry are started by means of compressed air. A nominal air vessel pressure is 30 bar sometimes 25 bar. The starting is performed by direct injection of air into the cylinders through the starting air valves in the cylinder heads or by a pneumatic starting motor driving the engine through a gear rim on a flywheel.
It may be preferred to install one separate compressor and an air receiver for the control air, auxiliary engines and for the instrument air supply for board purposes.
In general there are separate air vessels for the auxiliary engines, however this is not a requirement, but a recommendation. The saving potential when uniting the air vessels is not a considerable. When the size of the vessels increase also the classification requirements rise, for instance, all the pressure vessels over the 915 mm of inside diameter are to be provided with a manhole or at least with two hand holes.
At least two starting air compressors of approximately equal size must be installed. Classification requirement for refilling the vessels is one hour in a condition, under which the main propulsion plant, boilers and auxiliaries are not in operation due to an absence of power. Despite of the classification requirements, it should be possible to fill the starting air bottles from the minimum to the maximum pressure in about 15-30 minutes. If the starting system serves two or more of the purposes, the capacity of the system is to be the sum of the capacity requirements.
It is recommended to install an additional topping-up air compressor to pressurize the main air receivers. By topping-up compressor it is possible to avoid starting the main air compressors when operating at low compressed air consumption.

Starting air capacity requirements

The design and dimensioning of the starting air system have to be done by following the rules of the classification societies. Air vessels used to starting the engines need to have sufficient total capacity without recharging, so that feasibility for the number of starts required is as shown below:

  • Propulsion engines, 
reversible -------------- 12 starts
  • Propulsion engines,
non-reversible ---------- 6 starts
  • Engines for driving electric generators ----- 3 starts each
  • Engines for driving emergency generators - 3 starts each
  • Engines for other purposes ------------------ 3 starts each

In multiple engine installations where there are more than one engine per propeller shaft the total starting-air capacity needs to be sufficient for at least the number of consecutive starts determined by taking two-thirds of the number of engines multiplied by twelve for the reversible engines and by six for the non-reversible engines.

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16 Jun '17, 00:03

June 16, 2017, 12:03 a.m.
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