The Operating Principles of Marine Engine Air Start Systems
I have sailed on quite a few marine diesel engines, including B&W, Sulzer, and Stork/Werkspoor. All had variations of the system I am about to describe, but the principles are much the same.
I drew a sketch from memory (45 years ago) but updated it from a very good website referenced at the end of the section. The sketch also appears at the end of the section and can be referred to during the reading of the notes.
We begin then with the bridge ringing down standby on the engine room telegraph. (We used to change over fuel from Heavy Fuel Oil to Modified Diesel Oil for maneuvering.)
1. If in port, ensure turning gear is not engaged.
2. Open both air receivers’ isolation valves and start up a compressor to fill receivers to maximum; drain oily water of reservoirs and also from dead leg on supply pipe work.
3. This allows the compressed air to flow as far as the turning gear solenoid valve. Provided the turning gear is disengaged, this will allow the supply of air at 30 bar to the automatic valve passing though the non-return valve and into the manifold. From here the air is piped to the air chamber in the air start valve. (This is the pipe that will get hot if you have a leaking air start valve.) The valve is held in the shut position by the spring tension.
4. When an ahead or astern movement is rung and answered on the engine room telegraph, the telegraph start signal sol v/v is activated allowing air to the ahead and astern solenoid valves mechanism.
5. The air is now directed to the starting air distributer that is fitted on the end of the camshaft. This enables it to select the appropriate cylinder(s) to supply air to. This will be the relevant cylinder that is just passed TDC and on the downward stroke.
6. The air from the starting air distributer is at 30 bar, and this is injected into the air start valve top piston. This overcomes the spring tension and forces the piston downwards thus opening the valve and introducing the air at 30 bar to the cylinder(s) having been supplied earlier to the air chamber.
7. Depending on the engine make and model, air can be supplied to several cylinders to assist starting. A "slow start" supply can be used if there has been a lapse of half an hour between movements when maneuvering.