Starting Air System


Diesel engines are started by supplying compressed air into the cylinders in the appropriate sequence for the required direction. A supply of compressed air is stored in air reservoirs or 'bottles'. The starting air system usually has interlocks to prevent starting if everything is not in order.

Main Components of Starting Air System
The Components used in starting air system are listed below
  • Air receiver or air bottle
  • Air distributor
  • Air start valve
  • Other valves
  • Pilot valve
  • Automatic valve
  •  Start control valve  
  • Air flow control valve

System Diagram




Fig: Starting air system for MAB B&W 9L 58/64 diesel engine

Description
Air flow from air blow at 30bar to the automatic valve (4) and valve (3) which are closed. Air also flows to the control valve (1) as long as the turning gear is disengaged. When the start signal is applied the control valve (1),a air signal also applied to the control valve (2).Now the air can flow to the pilot valve and control valve(3) which vent the control valve(4) to allow air flow to the air start valve installed in the cylinder head.
Air also flows to the governor booster servo to pull the fuel rack at Zero position, so that no fuel can enter to the combustion chamber.

Fig: Pilot valve operation by camshaft

When the pilot valves cam in the right position, air flow through the pilot valve to the operating piston of air starting valve, opening valve allow the compressed air to enter in the cylinder forcing the piston down ward and turn the crankshaft. Just before the exhaust valve opens, pilot valve and air starting valve will vent. At this time another air start valve will open and turn the crank shaft. At which the control valve (1 & 2) will vent the automatic valve (4) will shut to allow the governor to operate the fuel rack.
The emergency stop valve is independent of the governor, can be operated by hand. When emergency signal is applied it allow the air flow to the servo cylinder at the back of the fuel pumps which pull the fuel control rack at zero position

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