There are several possible causes of an engine failing to turn on air:
1. Main Air Start valve closed: operator error. When preparing an engine, blow the engine over using compressed air before shutting the cocks. Check that the isolators on the correct air receivers are open and that the automatic valve is in the automatic position.
2. Turning gear engaged, or if disengaged, the air operated interlock switch may not be venting. Check that the turning gear is out and that no interlock warning lights are showing.
3. If a CPP is part of the installation the pitch may not be set to zero (an interlock). Check that the pitch is at zero.
4. On a reversing engine, the camshaft may not be in the correct position for the direction required. Check that the camshaft is in the correct position for the direction required.
5. A pneumatic or solenoid valve allows an air signal to operate the main automatic valve. At the same time, an air signal allows air to the air start distributor which will allow the cylinder valves to open in the correct sequence. Before the air signal can reach either of these devices, switches, either electrical or pneumatic relays, must confirm that the previously mentioned interlocks are clear and that the camshaft is in the correct position. The engine should turn when the automatic valve is operated by hand. If not then the fault will probably lie with the pilot valve for a particular unit. It is not unknown, because of moisture in the air for these to corrode and stick.
6. The starting air pilot valve sticking shut for the particular unit, the engine will, therefore, have a "dead spot". Note the position of the flywheel (mark with chalk), turn the engine so another piston has just come over TDC, disengage turning gear and try again. If the engine now turns when operating the automatic valve manually, try again from the control room.
7. The engine is not receiving the start signal from the bridge or control room. If the engine will start locally, but not from the control room or the bridge, then the fault must lie with the air signal to the automatic valve.
