When the parking brake is set and hydraulic systems are deactivated, what happens to brake pressure?

• A. Pressure is maintained in both #2 and #3 systems at the same level.
• B. All brake pressures bleed off and no accumulator maintenance occurs.
• C. Pressure will bleed off in the #2 system but will be maintained from the #3 system brake accumulators because of a parking brake shutoff valve.
• D. Only the #3 system loses pressure while #2 remains pressurized.

Answer: (C)

The key idea is how the parking brake shutoff valve and the brake accumulators work together to hold pressure when hydraulic power is removed. When the parking brake is set, the shutoff valve isolates the parking brake path from the active hydraulic circuits and allows the stored energy in the #3 system brake accumulators to sustain brake pressure. With hydraulics deactivated, the pressure in the #2 system has no retention path and bleeds away, while the #3 accumulators continue to maintain pressure to the brakes. That’s why the brakes stay pressurized thanks to the #3 system, not the #2.