Shuttle valves and differential pressure
(I hope this is the appropriate place for this question - rather techy but not a/c specific)
I am looking at shuttle valves being used for handing-over pneumatic or hydraulic supplies in the event that one fails (in one interesting case, hading from a hydraulic primary supply to pneumatic stand-by supply).
They look like nice robust and simple solutions, but how are they setup in practice? If both primary and standby systems run at the same pressure, will the valve 'flutter' between the two? Or is this avoided by building-in pressure differences between each possible supply? I can see advantages and disadvantages to both. I guess there is a difference between multiple 'redundant' systems in which all are working under normal circumstances, but capable of taking-over from each other in the event of pressure loss in one, and true standby systems which sit and wait for the primary to fail and then take over.
Thanks!