1. STARTING AIR SYSTEM
(a) Sketch a starting air system
(b) Describe the above system
The above sketch is air starting system for a large two stroke diesel engine.
The starting air is stored in the large steel vessel at the pressure 30 ` 40 kg/cm2 . The capacity of air
bottle is 12 times starting foe reversible engine and 6 times for non reversible engine , without replenishing.
When the main air stop valve is opened , air pass along pipe A to the master control valve on the
manoeuvring platform and through master valve to pipe B , lead to top of the automatic valve. The air is also
pass through pipe C to chamber D of automatic valve. Automatic valve is closed by balance air pressure plus
compression spring force from top .
When the engine control lever is pushed to start position , by the lever arrangement , the master control
valve is lifted up , stopping the air from pipe A and vent the air from the top part of automatic valve. This venting
effect is drop the pressure on top and valve is lifted upward. Drain to silencer is closed and air from chamber D
is allowed to air distributor valve and through air manifold to cylinder air starting valve. Cylinder air starting valve
cannot open yet since it is balanced and spring pressure keep it close.
Cho Myint
First Engineer
M.F.S.L

2. STARTING AIR SYSTEM
In distributor unit , the distributor valves with roller are contained in suitable casing and placed radially round the
cam shaft . There are two cam arranged in series on the cam shaft , one for ahead & another for astern , and
required cam can be placed in line with the distributor valves by shifting the engine reversing lever. Each cam
having a dent on its periphery . When high pressure air apply on the distributor valves , it force the rollers down
on the cam periphery and one of the roller will definitely enter the dent. This allow the distributor valve to shut of
the vent and let the pilot air to cylinder air starting valve , enter to upper part of the control piston . This pressure
will over come the spring pressure and push the valve down ward to open .
Cylinder valve is usually timed to open around 5 ‘ after T.D.C until 130 ‘ of crank angle, the roller will
clear from dent . Distributor valve will shut the pilot air and vent out . So overcoming pressure on the piston is
vanished and starting air valve will be closed back sharply by spring action.
As the engine revolve , the distributor valves are arrange to continuously operate its corresponding
cylinder starting air valves , according to the firing sequence .
When engine rotation reach about 30 % of normal speed , when its compression temperature enough for
combustion of the injected fuel , push forward the control lever for fueling. Injected fuel will ignite and engine will
be running on fuel . At this moment , the lever arrangement disengaged , master control valve will push down ,
top open & vent close ,let air from pipe A through to pipe B and closed automatic valve . Trapped air will drain to
silencer. Air distributor valve will push up by spring force and clear away from rotating cam.
When the engine is stopped or control lever is put back to stop position , the control mechanism will be
engaged and ready for start again.
Cho Myint
First Engineer
M.F.S.L