In this section, we will discuss the types of starting systems that derive their power from the pressure of compressed air. The first part of our discussion will cover the ways in which starting air is delivered to the starting system.

SOURCES OF STARTING AIR

Starting air comes directly from the ships medium-pressure (MP) or high-pressure (HP) air service line or from starting air flasks which are included in some systems for the purpose of storing starting air. From either source, the air, on its way to the starting system, must pass through a pressure-reducing valve, which reduces the higher pressure to the operating pressure required to start a particular engine.

A relief valve is installed in the line between the reducing valve and the starting system. The relief valve is normally set to open at 12 percent above the required starting air pressure. If the air pressure leaving the reducing valve is too high, the relief valve will protect the system by releasing air in excess of a preset value and permit air only at safe pressure to reach the starting system of the engine. Additional information on pressure relief valves and pressure reducing valves will be provided in chapter 13 of this rate training manual.

In the following sections, we will discuss two common types of systems that use air as a power source for starting diesel engines-the air starting motor system and the compressed air admission system.