[KenWittlief]

Ok some good objections have been raised here- if anyone hasnt been following the problem, let me state it simply

if you put 60 PSI in one end of a cylinder (say to raise an arm) and then switch its valave the other way, and use an additional valve to close its exhaust vent

then the air in that cylinder has no way to get out. If someone grabs that arm and pulls it down, the air in the bottom side will be compressed past 60 psi - maybe WAY past 60 PSI

OK - this IS a serious problem, but I think I have the solution. The regulator that is use to set the pressure to 60 PSI is designed such that IT will vent air if pressure exceeds the setting on the output side

if you have setup the pnuematics as they are normally used, and someone pulled down on the raised arm, the air that is compressed in the cylinder above 60 PSI would vent out the regulator (backwards)

so the solution for the mulitposiitoning system would be to have an additional (extra) regulator between the vent connections and the blocking valve, with the output of the regulator towards the cylinder. This will release any pressure above 60 psi in that side of the system, even when the blocking valve is closed.

If you take this approach I think you will want to have your pnuematic design WELL documented so you can explain to the judges exactly what you have, and why its safe.

Ive taken the liberty of editing Ngreens diagram to show where the extra regulator would be added - note the arrow -the regulator is connected backwards, and the input side is not used.

also note the regulator will not show pressure all the time, so you will have to adjust it to 60 PSI when the vent side is charged.