The air starting motor is used in order to turn the engine flywheel at the rpm that is required to start the engine.
The air starting motor can be mounted on either side of the engine. Air is normally contained in a storage tank. The duration for rotation of the flywheel is determined by these factors: volume of air in the tank, air pressure in the tank, air restriction in the system, engine rpm and resistance of the flywheel.
For engines that do not have excessive loads during start-up, the regulator setting is approximately 1034 kPa (150 psi). This setting is a favorable compromise between the cranking speed that is needed to start the engine and the volume of air in the tank.
For engines with loads that cannot be disconnected for start-up, the regulator setting must be increased in order to generate the required speed for start-up.
If necessary, the regulator setting can be adjusted to a maximum of 1550 kPa (225 psi) in order to produce the cranking speed that is needed to start. With the correct setting, the air starting motor can turn the loaded engine at the same speed and duration as an engine that does not have a load.
For good life of the air starting motor, provide an air supply that is free of dirt and of water. Use a lubricator with the starting system. Select a lubricant according to the following recommendations:
- For temperatures above 0 °C (32 °F), use SAE 10W nondetergent oil.
- For temperatures below 0 °C (32 °F), use air tool oil.
Air Starting System's Components
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| Illustration 1 | g00887305 |
Typical schematic for an air starting system (1) Quick release valve (2) Manual barring group (3) Solenoid valve for the air starting motor (4) Starting motors (5) Lubricator (6) Relay valve (7) Shutoff valve (8) Strainer (9) Air pressure regulating valve | |
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| Illustration 2 | g00729746 |
Typical air starting system (5) Lubricator (6) Relay valve (7) Shutoff valve (10) Air starting motor (11) Air silencer | |
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| Illustration 3 | g00733946 |
Control Panel (12) "PRELUBE/START" switch | |
When "PRELUBE/START" switch (12) is in the ENGINE PRELUBE position, air pressure actuates the contactor for the prelube pump. The contactor sends electrical current to the electric motor which engages the prelube pump motor. When the engine oil pressure reaches 7 kPa (1 psi), the prelube pressure switch opens and the "PRELUBE" indicator illuminates. Pressurized air is allowed to flow to relay valve (6) .
When the "PRELUBE" indicator illuminates, move "PRELUBE/START" switch (12) to the ENGINE START position.
Note: The engine prelube system will operate while the "PRELUBE/START" switch (12) is in the ENGINE START position.
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| Illustration 4 | g00729761 |
Air starting motor (13) Air inlet (14) Rotor (15) Vanes (16) Gears (17) Piston (18) Spring (19) Starting motor's pinion | |
The air from the supply passes through shutoff valve (7) and strainer (8) to relay valve (6). "PRELUBE/START" switch (12) is connected to the inlet side of the relay valve. The flow of air is stopped by relay valve (6) until the electrically driven relay valve goes through the interlock for manual barring group (2). Then, the air flows to piston (17) behind starting motor pinion (19). Air pressure on the piston compresses spring (18) and pinion (19) is engaged with the flywheel ring gear. When the pinion is engaged, air flows through another line to relay valve (6). The air activates the relay valve which opens the supply line to the air starting motor.
The air flows through lubricator (5) in order to lubricate the air starting motor.
The lubricated air flows into the air starting motor through air inlet (13). The pressure of the air exerts a force against vanes (15) in rotor (14). This turns the rotor which is connected by gears (16) and a drive shaft to the starting motor's pinion. The pinion turns the engine flywheel. The air is exhausted through the outlet and through air silencer (11).
When the engine starts running, the flywheel will start to turn faster than the starting motor's pinion. The air starting motor is equipped with a clutch with overriding capabilities. When the engine reaches 165 rpm, the contactor opens. When the contactor opens, air is vented from piston (17). This venting of the air causes the starting motor's pinion to retract.
When "PRELUBE/START" switch (12) is released, the air pressure and the air flow is stopped. Spring (18) retracts the starting motor's pinion and relay valve (6) stops the flow of air to the air starting motor.