Thanks EW73.
Just a few comments....
It's impossible to use only one pedal to park the brakes. If you push only one pedal, the unraised pawl on the un-pushed pedal mechanism interferes with the locking of the pedals (the Maintenance Manual even asks you to try one pedal parking.. if you can, something is broken)
Also, I proved today on one aircraft, that with an active #4 hydraulic system, the park brake valve can be wide open (c/o of a pulled Park Brake CB) and you can still park the brakes. I don't think it's a case of a constant supply of pressure overcoming leaky antiskid valves, I think the antiskid valves are completely shut, which prevents pressure bleeding into the return lines (and past the Park Brake Valve).
With only accumulator supply feeding the brakes and antiskid module, the antiskid valves can leak (so fast, in fact, within 45 seconds, the brake pressure indication is down to almost the nitrogen charge pressure on the accumulator).
Hope this makes sense.
Cheers.
NSEU.