Marine Diesel Engine Starting Air System

• Master valve is for commencing the operation of start command.
• Air supply is provided to engine by opening air supply valve from main air bottle.When this valve is open air reaches auto main start valve.
• Master valve when operated allows control air of 7 bar to pass through turning gear interlock, reversing direction completed interlock etc.
• To start M\E - First turning gear is to be disengaged.Ahead or Astern command is given.Once the interlocks are satisfied or deactivated air will  be supplied to automatic main air start valve.
• Control air acting on auto start valve which is generally a ball valve opens 90degree through a rack and pinion arrangement activated by a pneumatic piston or actuator.
• Air is now available at starting manifold and distributor.
• Distributor consist of a negative cam or inverse cam.Negative cam ensures positive closing of distributor and also it aids in overlapping of units.
• When a particular unit slide valve in distributor comes in the cam profile + air [pilot air for distributor] compresses the spring of that slide valve , air is supplied to operate the cyl head start valve of that unit.
• As the camshaft rotates, that unit air line is vented via distributor and cyl head start valve for that unit closes.
• The next unit distributor slide valve will be activated as per firing order.
• When command lever is on to the fuel ie, Run - Starting air system is completely isolated.

Safeties on starting air system: 

• flame arrestor 
• bursting disc
• relief valve
• main auto start valve
• thermal patches on start air line
• interlocks
• air bottle safety valve
• non return valve in starting line 

 Interlocks:

• turning gear interlock
• running direction interlock-prevents fuel from being supplied if engine's running direction doesn't match  telegraph order.
• reversing completed interlock-this prevents starting from taking place if distributor shifting has not been completed.
• Aux blower interlock- Ensures sufficient air in low speed running.
• Spring air interlock, safety air interlock, main l.o pressure interlock, jacket cooling water pressure interlock.

Starting air cam:

-ve cam ensures positive closing of air distributor slide valves and aids in overlapping of units.