May I pose a practical question? Why do we think the GDC has this rule in place? Why not allow the use of additional pressure relief valves in line with the cylinder rod/head supply lines, mounted on your bot right next to the "main" relief valve? You could use quick-release toggle valves (e.g.
http://www.mcmaster.com/#pneumatic-t...valves/=b7a2dk) to make it super-easy to relieve pressure in an emergency... One could even devise some kind of mechanical toggle that connects to the valves and flips all the connected reliefs at once.
So, is it a safety / emergency thing for use at the end of the match or in an emergency situation, or does the ability to trap air at mid-stroke during normal use pose some other safety concern?? I can't imagine the latter, or there wouldn't be much market for closed-center solenoids...!