TM 5-3805-260-24AIR CHAMBER AND MASTER CYLINDER OPERATION1. Air chamber inlet4. Air chamber assembly.9. Master cylinder 12. Plate.17. Valve.passage from brake5.Spring.assembly.13. Cup.18. Cup.valve.6. Supply passage.10. Master cylinder outlet 14. Indicator.19. Spring.2. Diaphragm.7. Cap.passage.15. Piston.20. Residual3. Boot.8. Bypass passage. 11. Rod assembly.16. Passages.pressure valve (check valve).When the brake is pushed, it sends air from the brakecontrol valve through passage (1) to the air compartmentof air chamber (4). Pressure air will push on the back ofdiaphragm (2) and rod assembly ( 11) and move thediaphragm (2), rod assembly) (11). indicator (14) andpiston (15) to the right. As piston (15) moves cup (18)past bypass passage (8), brake fluid in the master)cylinder bore will go through passage (10) and residualpressure valve (check valve) (20) to the wheel cylinders.When the brake pedal is released, pressure air is letout of air chamber (4) and spring (5) moves diaphragm(2) and rod assembly) (11) to the released position.Diaphragm (2) and rod assembly (11) moves faster thanpiston (15) because of the brake fluid which must beremoved. This will cause a reduction in the pressurearea between cup (18) and residual pressure valve(check valve) (20). Brake fluid ahead of cup (13) is pulledthrough passage (6), passages (16) in piston ( 15) andpast valve (17).When the brake fluid moves back through residualpressure valve (check valve) (20), spring (19) moves cup(18) and piston (15) toward plate (12).When piston 15) contacts plate (12), bypass passage(8) is open to the master cylinder bore. Residualpressure valve (check valve) (20) keeps a small amountof residual pressure (back pressure) in the brakehydraulic system Cap (7) has passages to let airpressure out of the master cylinder reservoir. The brakefluid pushed2-139
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