Why would you use the heavy screw valve like on the 20oz bottle when paintball bottles can be equipped with an on/off valve that does the job equaly well, for less weight and size?

On the combined Pneumatic/hydraulic machine.

Yes, the was one. The Kraken.

1 thing tough, you'll need to keep the pneumatics and hydraulics seperated, otherwise you're probably falling under the accumulator rule. As in not allowed.