SpudFiles

agreed with the above re pistons in a T

Ok, I have a 3" tee and will have a 1.5" port. So the travel would be .375 with the d/4 equation or .58 (or .59 if I round up a hundreth) with the travel=pi*r^2/w equation. That helps significantly, thanks again.

So, this issue (the pilot volume one) keeps sloshing back and forth in my mind. What BC said makes sense. So does what clide said. I think the stuff I originally posted applies, yet minimizing volume makes sense.

I think the ideal is kind of a paradox: minimal volume with maximum flow. A tiny little pilot volume exiting through a big honkin' valve opening.

The following shall be some ramblings on this subject, relatively unencumbered by the thought process:

I think to locate the trigger somewhere convenient, we end up using a 'normal' size air hose like 1/4" or so. This is small enough to actually impede the flow that would be ideal for emptying the pilot, since we would prefer it to empty instantaneously. Hence the smaller the volume of air that needs to exit the pilot, the faster the valve will trigger.

Even if we increase the hose size massively enough to eliminate the impedance, the same bottleneck will happen at the valve unless we equally increase the valve opening.

Then even if we do that, the bigger valve is going to take longer to open. No matter what kind it is, a valve takes time to open, so a bigger one takes more time. So the pilot will start emptying before the valve is fully open, which is very much like if the valve opening were smaller, so the same bottleneck will apply to some degree.

All in all, I think this is in fact a fairly involved fluid mechanics problem, the best solution to which would, like most real world problems, involve careful compromises and tradeoffs to optimize what can be done against perfect theory.

My gut feeling is also that many of the setups people are actually using in fact do a good job addressing the real world limitations and achieve this optimization quite well.

I thought I was going to get to work on a spudgun tonight, but alas, no. Was on the job 'til 6:30 and I'm pretty whipped. Want to hear something cool, though? My work partner, whom I've been sharing a bit with about this whole projectile thing, returned to the job today after a parts run and said "Look what I found in the irrigation aisle at Lowe's" and handed me a printed out page from Spudtech! Someone was shopping parts for a tennis ball launcher! It was cool.

Peace,
Sanaka

Well in some cases, when you decrease the pilot volume, you will limit the travel of a piston. Like in my case with a 3" tee which in turn brings up the real world limitations you mentioned. Regadless this now has me thinking of new ways to pilot a valve and such.