Air-Over Hydraulic Cylinder

The Brake System:

Air-Over Hydraulic Cylinder

The air-over-hydraulic cylinder assembly of a trailer consists of a brake air chamber and hydraulic master cylinder. The master cylinder is like any typical hydraulic brake master cylinder and is used to force fluid under pressure to the wheel cylinders in the wheel brakes. The brake air chamber changes air pressure into mechanical motion to operate the master cylinder. On tandem-axle trailers an air-over-hydraulic cylinder may be used on each axle.

The brake air chamber contains a diaphragm secured between the outer edges of the body and cover. The diaphragm is airtight and divides the chamber into pressure and non-pressure sides. The pressure side of the chamber has a threaded opening for connecting the brake apply air line. The nonpressure side is vented to the outside air. A compression spring in the nonpressure side holds a pushrod against the diaphragm, and returns both the diaphragm and pushrod to the pressure side of the chamber. One end of the pushrod extends from the nonpressure side of the chamber.

The master cylinder is mounted on the brake air chamber so that the pushrod aligns with the master cylinder piston. When compressed air enters the pressure side of the brake chamber, the diaphragm moves toward the nonpressure side. This extends the pushrod, moving the master cylinder piston, and forcing brake fluid to the wheel cylinders to apply the brakes. When the compressed air in the chamber is released, the compression spring returns the pushrod and diaphragm to the pressure side of the chamber allowing the brakes to release.

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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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