Hydraulic power unit oil path has size 6,10,12,16.
In order to make the hydraulic system to work properly, we have to control the hydraulic fluid in the pipe flow velocity, usually 4 to 6 meters per second.
Oil flow rate by the system operating pressure, oil flow path and the system maximum flow to decide; in certain oil path, the pressure and flow speed is proportional to the flow size of system work.