velocity3x wrote:Technician..."
From what you are describing as symptoms indicate the valve seat is relatively small in relation to the OD of your piston. "
2 inch dia shuttle valve w/ 1.875" dia o-ring.
<img src="
http://i145.photobucket.com/albums/r240 ... eValve.jpg?">
I appreciate your thoughts but, the problem is as I stated in an earlier post. The piston to cylinder wall clearance is only .005". Because the piston seat is recessed .200" deep, a strong vacuum is formed as air escapes past the piston sides to the barrel. It's the same thing you'd experience if you tried to pull a rubber stopper straight up out of a drain from a laundry tub with 72" of water in it. The escaping water tries to hold the rubber stopper in the drain unless the plug is pulled quickly. It's just an oversight in my design and can be fixed with some simple machining. The reason I mentioned it in earlier post is to show that I didn't use a QEV because their not fast enough to "rip" the piston from the valve seat
on this gun.
As for piston blow by.....very little of that happening in only .005". Seriously, this design doesn't have a breathing or any other problem. It's power is almost beyond evil. It's just a design glitch that is easily changed. Even with the glitch, it works exceedingly well.
Great analysis of the problem. I think you are on to it. A trip to the lathe for a face shave may fix it.
Dumb question, why does the air have to squeeze past the piston to get to the barrel? Isn't the chamber air fed directly to the area of the valve seat? If it feeds further back to where the waist is on the piston, that makes a ton a sense. Is there a way to machine ports past the face of the piston to eliminate that problem?
Very nice. It is possible to go too large in diameter on the seat. As the seat becomes larger, the force that initially cracks open the valve is very small. The pilot would need to drop to a very low value to crack it open. A fairly low pressure is required in the pilot to open it. Thanks for the great drawing. you may need a floating o ring to reduce the blow by even further is you wish to fire it with a QEV. From the ratio shown, that thing kicks when it fires.
Nice job. Keep the big pilot valve and enjoy that thing.
1.875 O ring on a 2 inch piston. I'm impressed. It snaps to attention. Those close to 1:1 ratio valves can be tricky to get to work (I've done a few) but when they work, they can't be beat for power.
:wav:
That is an even tighter ratio than any of the ones I built except the QDV, and they require hand pulling.
