(d) Parking Brake System.

TM 1-1520-238-T-4 3–21 3–7. SYSTEM DESCRIPTION 3–7 (c) Master Brake Cylinders. When the cylinder is static, an internal spring maintains the extension of the piston rod and pressure is not present. When the top (toe pressure) of a directional control pedal is pushed, hydraulic fluid is pressurized. As the upper piston head moves downward, the cap seats against the upper piston head, stopping the flow of fluid to the reservoir. When the reservoir closes, pressure builds in the upper chamber. This pressure buildup causes hydraulic fluid to flow through screens in the piston assembly. It also partially unseats an internal poppet valve. As pressure continues to build in the upper chamber, the piston assembly seats, trapping fluid in the lower chamber. Increased pressure causes the piston to fully open the poppet, allowing unused fluid to flow from the upper chamber back to the reservoir. Hydraulic braking pressure is supplied to the wheel brakes from the lower chamber through an outlet port. When the directional control pedals are released, a spring inside the upper chamber extends the cylinder to its original length, relieving fluid pressure and de–pressurizing the system. (d) Parking Brake System. The parking brake system (fig. 3–17) sets the wheel brakes for stability. During normal braking operation, with the brake pedal actuated, the lever of the parking brake valve is held in the off position by a spring assembly. The lever is attached to a camshaft which holds the two outer valves open. Fluid pressure is applied to the MLG wheel brakes by applying pressure to the toe portion of the pilot or CPG directional control pedals. The master brake cylinders force fluid through the transfer valves, parking brake valve, and connecting brake lines to the wheel brakes. With the parking lever in the unlock position, the inner valves are seated (closed) and the compensators are inoperative. FROM RIGHT MASTER CYLINDER RIGHT WHEEL M58-207A ASSY (4 EA) BALL & SEAT LEFT WHEEL PARKING BRAKE VALVE HANDLE PARKING BRAKE PILOT STATION Figure 3–17. Parking Brake System Operational Schematic 3–8. MULTIPLEX READ CODES 3–8 Not applicable.