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Every ship requires Compressed Air for starting Diesel Engines, as Control Air for Automation Control of all the machinery, for operation of Power Tools for maintenance work and as service air. High pressure compressed air is required only for starting diesel engines whereas low pressure air is required for remaining applications. Clean and dry air is stored on the ships in Air Reservoirs at required pressure.
Compressed Air System
Compressed air system consists of Air Compressors, Air Reservoirs and Pipelines with Valves. The pipeline system is separated in two zones namely, high-pressure zone for engine starting and low-pressure zone for other applications. Clean and dry air free from oil, is required for Automation Controls. This is achieved by using filter dryer units to get the appropriate quality air for this purpose.
Air Compressors compress the air to the required high pressure and, using a Reducing Valve produces the low-pressure air for various applications. Alternately, low-pressure air for Automation Controls may be produced by separate and special oil free Air Compressors fitted with filter dryers.
Generally, Reciprocating Type Compressors are used for producing high-pressure air and, to produce oil free low-pressure air for automation controls, Screw Type or Centrifugal Type air compressors are used. All the air compressors are usually installed in pairs with one in operation and the other as standby unit. Also, the maintenance becomes easy due to these machines installed in pairs.
The moisture in the compressed air is not desirable for any application for prevention of corrosion in the system. Therefore, drains are provided at various points in the distribution system to get rid of the moisture. Special filter dryers are provided for compressed air for automation controls.
Compressed air is stored Air Reservoirs which are specially designed pressure vessels. Two or three Air Reservoirs are provided on each ship, their capacities depending on the type of propulsion machinery. There is generally separate compressor and air reservoir provided for clean, dry and oil free air for automation controls. These Air Reservoirs are kept pressed up to the required pressure by automatic operation of the air compressors.
For protection of the compressed air system against over pressure, safety devices are provided at various points. Bursting disc type over pressure safety devices are provided on cooling system. Safety valves are provided for different stages on the compressors and on air reservoirs as protection from over pressure. Fusible plug type protection devices are provided after the air compressor discharge as well as on the Air Reservoirs.