The isolation valve with ball for high pressure 1/2”G is usually used to exclude parts of the steering system in which the tubing reaches the working pressure.
The isolation valves with ball, on steering systems, can be used both to exclude parts of the system in case of failure and, eventually, to change the flow direction of the oil towards and auxiliary hydraulic system (if the system is configured accordingly), but the line must be without pressure.
The isolation valves are also very useful during the maintenance of the system to avoid leaks of oil.