Air Compressor

The Brake System:

Air Compressor

FIGURE 14. AIR COMPRESSOR.

The air compressor pumps up the air pressure needed to operate the air-hydraulic cylinder. The compressor is driven by the vehicle's engine and turns all the time the engine is running.

It is generally belt driven, but can also be gear driven.

The air compressor used on some trucks is of the single-action, piston-type, and cooling and lubricating are accomplished by the engine's respective cooling and lubricating systems. The compressor is mounted to the left side of the engine. An unloader valve in the cylinder head vents compressed air when pressure exceeds the predetermined level.

On some compressor models, the lubricating oil is carried from the engine main oil gallery to the compressor by a flexible line. Oil leaking past the compressor bearings drains into the compressor mounting base. A return line connected to the mounting base returns the oil to the engine crankcase.

On other compressor models, lubricating oil is carried to and from the air compressor through passages in the compressor mounting base. The compressor mounting base oil passages align with oil passages in the engine crankcase and the compressor.

The compression of air in the compressor creates so much heat that the compressor must be cooled. Some compressors are air cooled while others are water cooled from the engine's cooling system. Air-cooled compressors have cooling fins around the cylinders and the cylinder head. Water-cooled compressors have water jackets either in the cylinder head or around the cylinders. A water inlet line and a water outlet line connect the compressor water jacket to the engine cooling system.

The compressor has air-check valves, one intake and one exhaust valve for each cylinder. The valves are held closed by light spring tension. In each cylinder the intake valve is opened by the suction created by the cylinder piston on its downward (intake) stroke. The exhaust valve is opened by air, compressed in the cylinder on the piston's upward (exhaust) stroke. An air strainer is mounted over the air compressor air intake port. The air strainer inlet is connected to the engine air intake system.

During the intake stroke of either compressor cylinder, air is drawn through the air strainer and intake valve and into the cylinder. On the exhaust stroke, the air compressed in the cylinder holds the intake valve tightly closed and opens the exhaust valve. The compressed air then flows through the exhaust valve into the compressed air system through an air discharge line connected to the compressor.

An unloading mechanism on the cylinder head unloads compressor compression whenever the air pressure reaches a predetermined maximum. The unloader mechanism generally has a diaphragm connected to linkage, so that when air pressure is applied at one side of the diaphragm, the diaphragm is moved to hold either the unloader valves or the intake valves open. At this time, the compressor will continue to run with the engine but will not compress air. When the air pressure drops to a certain predetermined amount, the pressure is released from the diaphragm, permitting the intake or unloader valves to close and the compressor pumps up the pressure again.

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Article Pages
1. The Brake System
2. Introduction
3. Principles Of Braking
4. Braking Requirements
5. Factors Controlling Retardation
6. External-Contracting And Internal-Expanding Brakes
7. Brake Types
8. Brake Drum Construction
9. Brake Shoes
10. Rotating And Non-Rotating Units
11. Self-Energizing Action
12. Disc Brake
13. Comparing Disc And Drum Brakes
14. Floating Caliper
15. Fixed Caliper
16. Hydraulic Brakes
17. Master Cylinder
18. Wheel Cylinder
19. Hydraulic Brake System Insepction
20. Before Road Test Inspection
21. Road Test Inspection
22. After Road Test Inspection
23. Air-Hydraulic Brake System
24. Air-Hydraulic Master Cylinder
25. Air-Hydraulic Cylinder
26. Air Compressor
27. Air Governor
28. Air-Hydraulic Brake System Components
29. Trailer Coupling Hoses And Connectors
30. Air-Over Hydraulic Cylinder
31. Operation Of Air-Hydraulic Brakes
32. Air-Hydraulic Brakes Of Large Trucks
33. Trailer Air-Over-Hydraulic Brake Systems
34. Air-Hydraulic Brake System Inspection
35. Before Road Test Inspection
36. Air-Hydraulic Brake System Road Inspection
37. Trouble Shooting Air-Hydraulic Brakes
38. Air-Brake System
39. Air-Brake Quick Release Valve
40. Air-Brake Relay Valve
41. Air-Brake Chamber
42. Air-Brake Slack Adjuster
43. Air-Brake Auxiliary Components
44. Semi-Trailer Air Brake Systems
45. Operation Of Straight Air-Brake System
46. Miscellaneous Air-Brake Components
47. Troubleshooting Straight Air Brake Systems

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