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| Illustration 1 | g01114440 |
The machines can be equipped with an optional Air-on-the-run system. This system allows the operator to inflate the tires while the machine is active. The system allows the operator to deflate the tires while the machine is active.
The Air-on-the-run section of this presentation is divided into segments. The first segment contains a drawing of the layout of the machine. This segment provides a general overview of the Air-on-the-run system.
The next 10 segments show the location of all components on the machine which are part of the Air-on-the-run system. A brief discussion of each component is provided.
The last section explains the operation of the Air-on-the-run system.
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| Illustration 2 | g01114442 |
The following components are part of the Air-on-the-run system:
- Control panel (1)
- Air compressor, hydraulic motor, and control valves (2)
- Air tank (3)
- Flushing pump (4)
- Holdback valves and rotary valves (5) (one on each front wheel)
- Holdback valves and rotary valves (6) (one on each rear wheel)
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| Illustration 3 | g01114455 |
The Air-on-the-run panel is mounted to the right side of the instrument panel. The Air-on-the-run panel contains the following components:
- pressure gauge (7)
- compressor switch (8)
- switch for tire pressure (9)
The pressure gauge registers the pressure in the tires. Tire pressure must be limited to a maximum of
The compressor switch is a two-position toggle switch. The top position of this switch is OFF. The bottom position of this switch is ON. The compressor switch receives power from the Air-on-the-run fuse. When the compressor switch is ON, power transfers to the switch for the air regulator.
The switch for the tire pressure is a three-position toggle switch. The center position of this switch is HOLD. The top position of the switch for the tire pressure is INFLATE. The bottom position of this switch is DEFLATE. The switch for the tire pressure will return to the HOLD position from the INFLATE position or from the DEFLATE position.
The switch for the tire pressure receives power from the Air-on-the-run fuse. When this switch is in the DEFLATE position, the deflate solenoid is energized. When this switch is in the INFLATE position, the inflate solenoid is energized.
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| Illustration 4 | g01114460 |
The Air-on-the-run fuse (10) is located on the instrument panel. This 15 amp fuse receives power when the main power relay is energized.
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| Illustration 5 | g01114466 |
Flushing pump (4) is located on the left side of the engine compartment. The engine compartment cover provides access to this component.
Oil from the top port of the flushing pump flushes the housing of each parking brake and the oil flushes each final drive.
The flushing pump provides the flow in order to operate the Air-on-the-run motor. Return oil from the motor is directed into the flushing circuit.
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| Illustration 6 | g01114473 |
The Air-on-the-run components are located under the deck of the operator's station. A hinged deck plate provides access to these components.
Air-on-the-run motor (15) is a gear motor. The flushing pump provides the oil in order to drive the Air-on-the-run motor. The motor operates when the compressor solenoid is energized. The motor drives air compressor (12) through a drive shaft.
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| Illustration 7 | g01114475 |
The air compressor is equipped with a pressure gauge (11). Fan (13) cools the air compressor when the compressor is operating.
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| Illustration 8 | g01114484 |
Control valve (17) for the compressor is located under the deck of the operator's station. A hinged deck plate provides access to these components.
Solenoid (16) for the compressor and relief valve (18) are installed in the control valve for the compressor. The solenoid for the compressor controls the oil flow to the Air-on-the-run motor. The motor operates when this solenoid is energized. The switch for the air regulator and the compressor switch control the solenoid.
The relief valve limits the maximum pressure in the Air-on-the-run hydraulic system to
Distribution Valve for Inflation
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| Illustration 9 | g01114488 |
Distribution valve (19) for inflation is located under the deck of the operator's station. A hinged deck plate provides access to this component.
The valve contains the inflate solenoid and the deflate solenoid. The 448-WH wire is connected to the inflate solenoid, and the 440-BR wire is connected to the deflate solenoid.
The switch for the tire pressure on the Air-on-the-run panel controls the inflate solenoids and deflate solenoids. When the inflate solenoid is energized, air from the air tank is directed into each wheel. When the deflate solenoid is energized, tire pressure is open to the atmosphere.
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| Illustration 10 | g01114497 |
Switch (20) for the air regulator is located under the deck of the operator's station. A hinged deck plate must be opened, and the cover on the switch must be removed in order to access this component.
The air regulator contains a pressure switch which senses the air pressure in the tank. This pressure switch allows the air regulator to control the solenoid for the compressor in order to govern the pressure that is in the tank. During the cut in cycle of the air compressor, the pressure switch is closed, and the solenoid for the compressor is energized. During the cut out cycle, the pressure switch is open, and the solenoid for the compressor is not energized.
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| Illustration 11 | g01114502 |
Air tank (3) is located at the front of the operator's station. The air tank stores the compressed air.
The system is equipped with an auto purge valve (21). This solenoid operated valve is located below the air tank. When the main power relay is energized, the auto purge solenoid is energized. This solenoid must be energized in order to hold air in the air tank. When the auto purge solenoid is de-energized, the tank is vented to the atmosphere. When the air pressure is released from the tank, water and sediment are also drained from the tank.
A relief valve (not shown) that is located in the air line on the left side of the air tank limits the air pressure in the tank.
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| Illustration 12 | g01114603 |
Each tire has an air supply hose (22), a rotary valve (23), and a holdback valve (5). The rotary valve distributes air to the tire. The holdback valve prevents a tire from going flat if an air supply hose fails.
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| Illustration 13 | g01114692 |
System voltage is available at the auto purge solenoid, at the compressor switch, and at the switch for tire pressure through 172-GN wires. The auto purge solenoid is energized when the main power relay is energized.
When the compressor switch is in the OFF position, the air compressor does not operate. When the switch for the compressor control is moved to the ON position, power transfers to the switch for the air regulator.
The switch for the air regulator measures the pressure in the air tank. When the pressure in the air tank is in cut in range, the switch for the air regulator is closed. Under these conditions, current flows to the solenoid for the compressor and to the fan for the compressor through the RD wire.
Note: Electrical wiring in the air compressor does not follow the Caterpillar corporate system for wiring.
During the cut-in cycle, the solenoid for the compressor is energized. At this time, the fan for the compressor operates. When the compressor is energized, the valve for the compressor directs hydraulic oil from the Air-on-the-run pump to the Air-on-the-run motor. The motor turns, and the compressor operates.
When the switch for tire pressure is in the INFLATE position, current in the 172-GN wire flows to the inflate solenoid through the 448-WH wire. The solenoid energizes, and the distribution valve for inflation directs air into the tires.
When the control switch for tire pressure is in the DEFLATE position, current flows through the 440-BR wire to the deflate solenoid. The deflate solenoid energizes, and the distribution valve for inflation directs air from the tires to the atmosphere.
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| Illustration 14 | g01114701 |
The engine drives the hydraulic pump. The hydraulic pump provides flow to the hydraulic motor. The hydraulic motor drives the air compressor. The air compressor supplies compressed air to the air tank.
When the pressure in the air tank reaches
The distributor valve controls the flow of air from the air tank to the tires. The distributor valve is controlled by the switch for the tire pressure. When the switch for the tire pressure is in the INFLATE position, the distributor valve directs air from the tank into the line to the tires. Air in the line to the tires flows to the holdback valves at each tire. Each holdback valve contains a spring assisted check valve.
When the pressure in the air line is greater than the pressure in the tire, the ball check valve opens. This action allows air to inflate the tire. If the air line to any tire is open to the atmosphere, the pressure in each tire seats the ball check valve. The pressure in each tire also acts on the spring assisted check valve in the holdback valve. Spring force closes the spring assisted check valve. This action prevents air from escaping when the pressure in the tire is