Well, on the Airbus documentation I have, (for A330), it shows a direct, open pressure path from the brake accumulators to the parking brake actuators when the parking brake handle is set to park brakes on. The alternate servo valves controlled by the BSCU are kept open, allowing accumulator pressure to bear directly on the parking brake actuators. The parking brake handle valve stays open when parking brakes are set on - it does not close to lock the pressure in.
Airbus A330 FCOM 1.32.30 P7 REV 03
PS, Airbus state that the accumulator will maintain parking brake pressure for "at least 12 hours", but aircraft are always routinely wheel chocked.
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