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| Illustration 1 | g01949822 |
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Air start system (typical example) (1) Relay valve (2) Hose (3) Starting motor solenoid (4) Hose (5) Air starting motor | |
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| Illustration 2 | g01192361 |
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Air starting motor (6) Air inlet (7) Vanes (8) Rotor (9) Pinion (10) Reduction gears (11) Piston (12) Piston spring | |
When the main supply of pressurized air is turned on, pressurized air is provided to relay valve (1). The main supply of pressurized air is blocked by the relay valve. The relay valve allows control air pressure to flow through hose (2) to another valve that is connected to starting motor solenoid (3).
Note: Refer to Testing and Adjusting, "Starting Air Pressure - Adjust" for information about the optimum supply air pressure.
When the normally closed starting motor solenoid is activated, the solenoid opens the connected valve. The valve allows the control air pressure to flow behind piston (11) inside air starting motor (5).
The control air pressure pushes the piston. The piston compresses piston spring (12) and moves the drive shaft for pinion (9) outward. The pinion engages with the flywheel ring gear. The starting motor does not begin to turn until the pinion gear is fully extended into flywheel ring gear.
After the pinion engages the flywheel ring gear, a port is opened to allow the control air pressure to flow through hose (4). The control air pressure is directed to relay valve (1). The relay valve opens in order to allow the main supply of pressurized air to flow through air inlet (6).
The pressurized air causes vanes (7) and rotor (8) to rotate. The rotor uses reduction gears (10) to rotate the drive shaft for the pinion. The pinion rotates the flywheel in order to crank the engine.
When the engine is started, the flywheel begins to rotate faster than the pinion and the flywheel ring gear begins to drive the pinion gear. The pinion is retracted from the flywheel. This design prevents damage to the air starting motor, pinion, and flywheel ring gear.
When the engine control senses the crank terminate speed, starting motor solenoid (3) is de-energized. The solenoid closes the attached valve and the control air pressure is removed from piston (11). Piston spring (12) retracts the piston and the drive shaft for the pinion.
The retraction of piston (11) closes the passage for the control air pressure to relay valve (1). The relay valve closes in order to shut off the main supply of pressurized air to the starting motor.