Piston valve sensitivity

[FighterAce]

Yeah I was quite greedy on the teflon tape so the darn thing went in too far. Usually I put on a lot and then it resists so much it feels like it went in too deep... this time it really did  lol

[FighterAce]

I replaced the T piece and made a new piston for it. When it fires, the piston looks like it doesnt even move but shoots really good. The sealing face is all the way forward to the barrel as if theres pressure inside but there is none. Is this good or bad 

[Forum Admin]

Its not a good thing as it constricts the flow, with your valve, you probably want the face of the piston to go back to where the T goes up. A coaxial doesnt have to move back as far to get optimal flow as the air enters from all sides. That is where I have found chronographing so useful in building valves, especially if you use audacity and analyze the sound from pilot to fire.

[FighterAce]

The piston can travel a good 15mm so theres no big concern about flow. I was thinking that maybe the piston bounces back off the back stop into the closed position once fired. I used a spring to fix this problem but once I get my shock pump, I dont think there will be enough air coming in at once to seal the valve

[Forum Admin]

Sometimes pistons do bounce, even during the firing cycle. This can lead to inefficiency. Sometimes it will even make a honking sound, other times, Audacity can pick up the fluttering. The main thing is that it stays its 15 mm back during the firing cycle. What it does after the ammo has left the barrel doesnt really matter. I'm actually making a coaxial right now (getting ready to run to the store for some krazy glue to finish it). Your project has gotten me back into wanting to make piston valves over using the QEV. 

[FighterAce]

Found the problem... I had a bad muzzle sealing face. I just machined a new one from 1/2-3/4 reducer.
Had a few problems with PTF comming off but once I fixed it, it was a whole new piston. I was expecting it to be weak since everything I do requires some tweaking to get it working so I put my hand in front of the muzzle to see how weak.
Oh boy I was wrong, it literally blew my hand out of the way  I hope it wont turn blue till tomorrow lol
The power seems to keep the piston at bay, I've checked it after firing and it stayed all the way back.

[Forum Admin]

Good job, nothing quite like making a powerful valve on your own.