Off the top of my head:
On the braking system there is a valve called the"Alternate brake selector valve" which when there is no R/H sys pressure it allows L/H sys pressure to provide brake (Alternate) pressure.
We (Engineers) can, by use of the park brake, take fliud out of either L/H or R/H sys and return it to the other by manipulating this valves position using Hyd differential pressure.
