To start the engine, an optional air starting motor may be used to turn the engine flywheel at the appropriate speed for starting.
Typical Air Starting System
(1) Air start control valve
(2) Air starting motor
(3) Relay valve
The air starting motor (2) can be mounted on either side of the engine. Air is normally contained in a storage tank. The storage tank must hold this volume of air at 1720 kPa (250 psi) when the storage tank is filled.
The regulator setting is approximately 690 kPa (100 psi) for engines which do not have heavy loads when the engine is started. This setting is a favorable compromise between the following conditions:
- The engine cranking speeds that are needed to start the engine
- Volume of air in the storage tank
If the engine has a heavy load which can not be disconnected during starting, the setting of the air pressure regulating valve needs to be higher in order to get high enough speed for easy starting.
The air consumption is directly related to speed. Also, the air pressure is related to the force that is needed to turn the engine flywheel. If necessary, the air pressure regulator can be adjusted to 1030 kPa (150 psi) in order to produce the correct cranking speed for a heavily loaded engine. With the correct setting, the air starting motor can turn the excessively loaded engine as fast as an engine that does not have an excessive load.
Other air supplies can be used with the correct pressure and volume. For good life of the air starting motor, the supply should be free of dirt and water. The maximum pressure for use in the air starting motor is 1030 kPa (150 psi).
Air Starting Motor
(5) Air inlet
(11) Piston spring
The air from the supply goes to relay valve (3). The air start control valve (1) is connected to the line before the relay valve. The flow of air is stopped by the relay valve until air start control valve (1) is activated. Then, air from the control valve goes to piston (10) and behind pinion (8) for the air starting motor. The air pressure on piston (10) compresses piston spring (11). Also, the air pressure on piston (10) engages pinion (8) with the flywheel gear. When the pinion is in engagement, air can go out through another line to the relay valve. The air activates the relay valve which opens the supply line to the air starting motor.
The flow of air goes through the oiler (4) in order to pick up lubrication oil for the air starting motor.
The air with lubrication goes into the air starting motor through air inlet (5). The pressure of the air pushes vanes (6) in rotor (7). This turns the rotor which is connected by gears (9) and a drive shaft to starter pinion (8) which turns the engine flywheel.
When the engine starts running, the flywheel will start to turn faster than pinion (8). The pinion (8) retracts under this condition. This prevents damage to the motor, to pinion (8) or to the flywheel gear.
When air start control valve (1) is released, the air pressure and flow to piston (10) behind pinion (8) is stopped. Piston spring (11) retracts pinion (8). Relay valve (3) stops the flow of air to the air starting motor.