This is a QEV not a homemade piston, I would have made one but for the life of me couldn't figure it out or be bothered figuring it out :p

How do I increase the fit of the piston?

On occasion my QEV doesn't activate. My QEV is a spring type and not purely moved by air, could this be the problem? Any idea what could be the cause and/or solution? It's extremely annoying! For times it works great non stop and then another time I will go to have a shoot and air just glides gracef...

Haha! Good way to put it. Ok thanks I'll make it as small as possible. and thanks for the diagram. EDIT: I've fixed the pilot chamber area, I couldn't make it any smaller, and sure enough it works great. Although I'm getting HORRIBLE performance out of it. i.e shooting a marble goes around 4 meters ...

The PVC is temporary as I wanted to find out how a QEV + Blowgun setup worked without spending to much money.

Intake point is where I'm filling from (obviously)[/img]

The blowgun problems gone and my cannon is complete
But the QEV is letting air down the barrel? and because of this it doesn't pump up. What is the problem? It really blows to have finished a build and find out something is wrong..

Ok I'll remember that for the next build. Making a piston just sounds hard though... Finally got my QEV, putting it all together now. The blowgun is going to be a bit tricky because the thread is so small no one stocks adapters for it! Still thinking about it.

What is your preference a QEV or a home made piston? They both seem to be good, except with a home made piston you have more control.

Awesome! Thanks a lot Crna. Your a gold mine of information!
Can't wait to start building this thing.
Does it pressurize immediately or does the leaking past the QEV take a while?

I must be a real bugger... but...
I was just thinking, when the pressure equalizes in the chamber and pilot chamber, will the gun spontaneously fire?? Because the piston inside the QEV wont be pressured against the barrel anymore?!

Thanks for all your help. I bought everything today except the QEV which I'm getting tomorrow, will put it all together in a day or so.

Blowgun sounds perfect!! http://www.spudfiles.com/forums/blowgun-question-t7481.html Looks good as well. I'm practically sorted now, thanks for all your help! EDIT: I've got a small problem. I was showing my dad what to do and he pointed out the air canister that all of the rifles have on this site....

Thanks a lot both diagrams explained everything perfectly; air goes in pushes QEV closed and blocks barrel - airs released at exhaust point creates pressure sucking the QEV open allowing air out of the barrel. Correct me please if I have the wrong idea. One last thing so I can stop being annoying. F...

A QEV sounds like the best bet if its the easiest option. Has someone got a basic diagram? I just need something to understand whats going on inside.
Thanks for your super fast replys!!

Hi everyone 1st post (although I've stalked this forum for a while), I have previously made a PVC gun which simply consisted of a chamber, car tire valve, ball valve and barrel. It's bulky, hard to fire and plain boring. It's school holidays now in Australia and I'm wishing to make a new rifle. I've...