This is the PA-28R-201 landing gear hydraulic system diagram.
I am wondering how this shuttle valve functions. Research I have done indicates that a shuttle valve blocks one attachment to the valve while allowing another to run through. Only one side or the other, not both or neither.
In the diagram below, everything beneath the shuttle valve is a closed system (other than the thermal relief).
Clearly, the valve cannot be closed on one side or the other or else the pump would be applying pressure through three pistons to a closed valve at the other end of the loop.
Is this shuttle valve different than what I have read them to be? Is it perhaps in actuality that both sides are either open at the same time or both are closed at the same time but never one closed while one is open? If one remains closed, how could the pump move fluid through the complete circuit?