Question id 127 - Aircraft General Knowledge - Airframe, Systems, Powerplant - ATPL - Airline Transport Pilot license

To Isolate A Part Of The System And Protect It Against Accidental Pollution.
To switch to the secondary system in case of a leak in the primary brake system.
To allow by-passing of a hydraulic pump in case it is subject to excessive pressure, without further damage to the system.
To prevent total system loss in case of a leaking hydraulic line.