For the dump valve I was going to use the PRV as its got a pull type manual override (http://www.ebay.co.uk/itm/Safety-Val...item1c34534bd6)
It will have a dual function, its installed on the buffer tank so all the system will be depressurised when open.

Turning the gas on through the flipper arm wouldn't be seen as a good idea. Same goes for turning the robot over.
True, its a real headache to try getting everything in its ideal location when space is limited! (and tbh this build isn't on of the smallest).

I've yet to figure out how to keep the PRV open to act as a dump valve, but it will be some sort of toggle mechanism...should not be too difficult to devise...still can do a normal valve if this idea is not acceptable, can put another Tee at the pressure gauge and dump from there.

PRV-Dump valve.jpg