Illustrated is a Sulzer RTA Air Start System. These do vary depending on the type of engine, so if you've had experience of one, it might be slightly different to the one illustrated here.
Start at the air receiver and open the valves. Air at 30 bar flows to the automatic valve which is in the automatic position. air flows via the turning gear interlock to the control valves for engine starting. If the turning gear is engaged, then the control air won't get past the interlock.
The captain wants to start the engine ahead. As he moves his little lever on the bridge, an electrical signal operates the start solenoid valve and the ahead solenoid valve. This allows control air to open the respective pneumatic control valves. Air flows to the control valve on the automatic valve allowing air under the piston to vent and thus open the valve. Main start air then flows through the non return valve to the air start manifold.
At the same time air from the direction control valve flows to the air start distributor. This moves the distributor servo piston into the ahead position, flows through the start cut off valve and operates the control valve to allow air from the air start manifold to operate the pilot valves.
Dictated by the distributor cam, air flows from the pilot valves in sequence to the control valves for the individual air start valves mounted in the engine cylinder.
After a set period of time (10 seconds), or when the engine has reached firing revs (whichever comes first), the start air is cut off and the governor puts fuel on the engine.