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Before you disconnect any line from the air compressor, purge the system of pressurized air. Failure to purge the pressurized air before you service the air compressor can result in personal injury. |
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Hot engine components can cause injury from burns. Before performing maintenance on the engine, allow the engine and the components to cool. |
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Personal injury can result from rotating and moving parts. Stay clear of all rotating and moving parts. Never attempt adjustments while the machine is moving or the engine is running unless otherwise specified. The machine must be parked on a level surface and the engine stopped. |
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Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates. |
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Keep all parts clean from contaminants. Contaminants may cause rapid wear and shortened component life. |
Air Induction System
One of the most important aspects of preventive maintenance is the induction of clean air. The air induction system should be inspected when maintenance is performed to the air cleaner. Check the air induction line to the compressor for leakage.
The air for induction must be drawn through the air cleaner and through the air intake pipe. Be sure that the air induction line and the fittings for the air induction line do not have any leaks.
Be sure that the air induction line that connects to the air compressor does not have any restrictions. Check the air intake hoses and clamps.
Perform the Following Inspections at an Interval of Every 6 Months, 1800 Operating Hours, or 80467 km (50000 miles)
Cooling System
The minimum size for the coolant lines that connect to the air compressor depends on the flow. The minimum size that is recommended is 9.35 mm (0.368 inch) inside diameter.
Inspect the port for the air discharge and inspect the line for the air discharge for buildup of carbon. A buildup of carbon may indicate inadequate cooling.
Check the coolant lines for restrictions to flow. Check the condition of the coolant lines. Check for leaks or damage due to wear or abrasion. Check the coolant lines for clogging from rust or scale.
Check the coolant flow and compare the coolant flow to the specifications for coolant flow.
Lubrication System
Check the oil supply line for restrictions to flow. Refer to the Specification section for the value for minimum oil pressure.
Air Compressor Drive
Check for noisy operation. Noisy operation may indicate worn drive components. Refer to the Testing and Adjusting section. Check the mounting bolts for the air compressor. Tighten the mounting bolts to the proper torque. Refer to the Specification section for the proper values for torque.
Air Compressor and Unloader for the Air Compressor Governor
Test the air compressor and the governor for proper operation. Test the air compressor and the governor for proper setting of air pressure. Refer to the Testing and Adjusting section.
Operate the air compressor through the load cycle several times. Operate the air compressor through the unloaded cycle several times. The unloader system should contain a governor. The governor should cut out at 896 kPa (130 psi). The governor should activate at approximately 758 kPa (110 psi). The air compressor should change between the two different compressor cycles quickly.
The operation of the compressor cycles may be checked by installing a test gauge in the unloader port on the air compressor. Observe the gauge during the change from the loaded cycle and the unloaded cycles.
The air pressure should be applied and the air pressure should be exhausted quickly. There should not be any lag between the buildup of the air pressure and the release of the air pressure.
Service Tests
General
The following tests do not need to be performed on a regular basis. Perform these tests when you have the following conditions:
- Air leakage is affecting the buildup of the air pressure.
- The air compressor keeps switching from the loaded cycle to the unloaded cycle because of leakage from the unloader plunger.
Operating Tests
The Federal Motor Vehicle Safety Standards require specific performance of the air brake system. All vehicles that were manufactured after the effective date of the FMVSS 121 must have an air compressor that is able to raise the air pressure of the air system from 586 kPa (85 psi) to 689 kPa (100 psi) in less than 25 seconds. This is at the minimum required reservoir volume for the vehicle.
Perform the test while the engine is operating at the maximum recommended governed speed. The vehicle manufacturer must certify the performance on a new vehicle. The vehicle manufacturer must make allowances for reservoirs that have a volume that is larger than the minimum required reservoir volume.
The buildup time for an air compressor that is new can be measured and recorded at high idle. Other tests throughout the service life of the air compressor can be compared to the test of the new air compressor. The buildup time for the air compressor should be recorded. This should be kept with the maintenance records of the vehicle.
The leakage of the air system must be below 21 kPa (3 psi) per minute during a brake application. Check the air system for excessive leakage and repair before the test.
Note: Components of the system may leak without an indication from the gauges in the vehicle.
The following components affect the air supply. These components must be checked for leakage separately:
- Governor
- Air Dryer
- Drain cocks on reservoirs
- Safety valves
- Check valves
Leakage at Cylinder Head of Air Compressor
- Lower the air pressure of the air system to 414 kPa (60 psi) while the engine is operating.
- Apply a soap solution around the cylinder head. Check for bubbles between the cylinder head and the valve body.
- Check for bubbles between the valve body and the cylinder block of the air compressor. Bubbles indicate leakage. No leakage is permitted. Repair any leakage in the cylinder head.
Leakage at the Inlet Valves or Leakage at the Discharge Valves
Test the air system for leakage before testing for leakage at the inlet valve. Test the air system for leakage before testing for leakage at the discharge valve. Leakage at the inlet valve or leakage at the discharge valve may be detected by long buildup times. Leakage at the inlet valve or leakage at the discharge valve may be detected by long recovery times.
- Start the engine. Operate the engine until the engine reaches normal operating temperature.
- Lower the air pressure of the air system to 621 kPa (90 psi).
- Increase the speed of the engine to 1800 rpm.
- Measure the time and record the time that is required to raise the air pressure from 689 kPa (100 psi) to 896 kPa (130 psi).
- Repeat steps 2 through 4 three times.
- Add the three values that were recorded. Divide that figure by three in order to calculate the average time for buildup of the air system.
- Compare the average time for buildup of the air system to the first three values. The values of all four times should be consistent. Evaluate the buildup times of the system for the air compressor. Replace the air compressor or repair the air compressor, if necessary.
Air Leakage at the Unloader
Air leakage at the unloader may be indicated when the air compressor changes from the loaded cycle and the unloaded cycle excessively.
Note: Be sure that the leakage of the air system is below the maximum value for leakage of the air system.
- Raise the air pressure of the air system until the air pressure equals the governor cutout.
- Allow the engine to idle. The vehicle should be parked.
- Monitor the air compressor. The air compressor should remain unloaded for at least 5 to 10 minutes. Repair the air compressor or replace the air compressor when the air compressor cycles to the loaded cycle too soon.