Air-Hydraulic Cylinder

The Brake System:

Air-Hydraulic Cylinder

The air-hydraulic cylinder is put into operation by the hydraulic pressure from the master cylinder. It uses compressed air to boost the hydraulic pressure from the master cylinder. The Army uses more than one model of air-hydraulic cylinders; all models contain the same major units and operate on the same principles. They are made up of three major units in one assembly. The units are the control unit, power cylinder, and slave cylinder. The units of the M809-series vehicles consist of an air valve, air cylinder, hydraulic cylinder, and piston.

The control unit contains a control valve (relay) piston, which is hydraulically operated by brake fluid from the master cylinder, and a diaphragm or compensator assembly, which is operated by pressure differences between brake fluid and air and spring pressure. A return spring holds the hydraulic relay piston and diaphragm assembly in the released position when there is no hydraulic pressure. Two air poppet valves, assembled on one stem, control the air pressure flowing into and out of the power cylinder. The poppet valves are normally held in the released position by the poppet return spring.

The power cylinder consists of a cylinder, piston, piston rod, and piston return spring. Air pressure admitted at the head end of the cylinder compresses the piston return spring extending the piston rod. When the air pressure is released, the spring retracts the rod. Air in the rod end of the cylinder can pass freely in and out of the cylinder through a breather air line that is attached to the air intake system of the vehicle. A lip-type piston seal prevents air pressure from leaking between the piston and cylinder wall.

The slave cylinder is a hydraulic cylinder containing a piston and piston cup. Some cylinders contain a check valve assembly, at the hydraulic outlet, for maintaining a slight amount of pressure (residual) in the hydraulic lines and wheel cylinders. The piston and piston cup are hollow and contain a check valve that allows brake fluid to pass through freely when the power cylinder is retracted. When the power cylinder extends, the check valve blocks the opening through the center of the slave cylinder piston.

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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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