maverik94 wrote:How would a QDV have a faster opening time?
Because, as with a piston valve, when the full front face of the piston is exposed to the chamber pressure, there's a hell of a lot more than 30 pounds forcing it open - the "finger" is merely the triggering mechanism allowing it to move back and expose the front surface.
They're pretty much both the same, except that pneumatic forces start the opening process of one, the other a trigger rod pulling back on the piston. After that's started, both have the same opening force, pressure acting on the front of the piston, pushing it back (because, of course, pistons are not "sucked" back - pressure can ONLY push).
The difference however is that a QDV has no residual pressure behind it, which increases net pneumatic force to a degree.
However, I would argue that this has relatively little effect on opening time with a well designed piston valve and that this difference is ultimately already beyond the point of diminishing returns as far as performance.
Not to say that people shouldn't use QDVs as appropriate, but they shouldn't be touted as inherently superior to a piston valve. I'd choose between the two on their genuine, not imagined, merits.