SpudFiles

Can anyone tell me if the piston in a QEV needs to seat the same way as it would in coaxial?i've read it doesn't in a QEV?

Qev and coaxial are two different things, in a coaxial the air chamber is around the barrel and a piston covers the end of the barrel also coaxial are mostly muzzle loaders.
qev's are when a diaphram blocks off the barrel from the air chamber, and the feed to the chamber is normally perpendicular to the barrel, qevs are normaly made for milti shot cannons.
Look at piston valves explained to see the pics.

Yep,I've built 2 coaxials and now I'm on to building a QEV,I just needed to know if the pistons sealed the same way,you sort of answered that being that the QEV is a diaphragm,thanks,that was an easy way to understand a quev,

andrew67 wrote:Can anyone tell me if the piston in a QEV needs to seat the same way as it would in coaxial?i've read it doesn't in a QEV?

QEV=Quick Exhaust Valve. That being said they are a ported valve that need to be adapted to the cannon. The piston/diaphram simply blocks the exhaust port in the simalar way as any barrel sealing piston does.

are you able to tell me if you think the barrel is to long?should it finish closer to the edge of the supply hole,should the spring only be strong enough to seal the piston against the barrel?

The sealing surfaces should meat in the middle of the tee. The spring should make the piston lightly touch the barrel and filling with air should make and hold the seal.

Thank you helps heaps

Should the piton protrude into the chamber behind it ? If you can see here there is a gap from on chamber to the next!

Should the piston protrude into the chamber behind it ? If you can see here there is a gap from on chamber to the next!

Looks OK to me.

Thankyou! I'll finish it off tonight and see how it goes!

One thing, is the face where the piston touches rough with sharp edges? This can compromise sealing and damage your piston seal.

Nah,no sharp edges I've filed the barrel flat with a fine file and taken the rough edge off,I'm using a nylon washer as a seal,that should be ok yeah?

I don't think filing the barrel flat will do, especially with hard seals like yours. With a nylon seal the barrel needs to be absolutely straight, as there's not much deformation on the seal to close gaps. You'll have better luck with a rubber washer.

Ok,thanks i think I'll just use rubber to save pulling it apart again,do you glue the spring to the piston or is it ok without glueing?i think I've asked just about everything I can think of to get it right first time!thanks for all help!