Originally Posted by
double_barrel
(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!
We utilise shuttle valves - known as "double check valves" to us - in the rail industry as a part of the locomotive pneumatic braking system. Their function is to pressurise the locomotive brake cylinders at the higher of two pressures, those sources being the train's automatic brake, or the locomotive's independent brake. With brakes released and no pressure in either system, the valve just sits there, even with identical pressures with brakes applied the small amount of inherent friction in the valve body prevents the slide from moving, it will just sit in the 'last moved to' position. I've not heard of 'valve chatter' ever being a problem and this system has been around for decades.
Here's a rough idea how they're set up for us...Ignore the 'relayair valve' bit, that's for another device.
