From memory when the gear was up and the uplocks held the gear the hydraulic pressure released and the gear would be held by the uplocks and not the pressure in combination with the uplocks.
When you hand pump the ram is pressurized to extend but I can't remember what disengages the uplock. There is a standpipe in the system to prevent complete loss of fluid like any system however I can't for the life of me remember about the uplock???