behind piston filling vs. in chamber filling

[Velocity]

why does joel use chamber sealing then????

good question... I have actually not thought of this before... i am not really sure

[Steve-]

it seems to me that a chamber sealing would open faster because the force is pushing directly on it and not from an angle but i don't know, i have created a chamber sealing design that requires zero part modding, only the piston and if it works i'll post it so you guys can tear it apart and tell me every little mistake or overlooked aspect of it.

[runningawaypyro]

so would you say that a piston cannon with the barrel inside the chamber be best? or would a t valve be harder to build for an over under?

[SpudStuff]

What..... We speak english not dumbass.

[runningawaypyro]

your little bleeding icon is oh so flattering...

[richardbridges]

Just build one of each and see which one you prefer.

[runningawaypyro]

well i would like to do that but 4" pvc is $$$$$$$$. i just called our local plumbing a store. $70 for a 20' length. and they only sell pices of 4" in 20'. a BIT pricey. how much do you guys pay for 4 inch pvc?

[schmanman]

like $10-15 for 10 feet of 4 inch diameter sch 40 4 inch pvc.

[SpudStuff]

Yes you are getting jiped. Ash them if they have any scraps.

[dinsdale]

I'm currently planning my first piston valve, and barrel sealing immediately seemed the way to go.
I'm thinking im gonna make mine out of steel though

[runningawaypyro]

well good luck with that. it sounds like pistons are where the power is at with out spending a $100. thanks for the tip i will ask for scraps. or ill go to seattle. theyl probly have a bigger selection in plumbing over there.

[schmanman]

somtimes it's even less than 10-15 bucks, that's the average price arround here, though

[Jolly Roger]

Hey guys I've used secondary chamber (rear of piston) filling for all my pneumatic guns but I'm making an auto / semi auto rifle which has continuous pressure flow (obviously). The one problem I'm having with the design is the potential for the pressure from the supply line to to push the piston foward and seal on the barrel before the chamber has been fully dispensed. How do I avoid this problem? I've posted a topic on this problem "High pressure dump valves" or something like that which has a link to a 3-way push buttong valve that may be able to block off the supply line and open and exhaust line but I'm not quite sure. Can anyone help me, this is the only area thats holding me up on construction...
Cheers, Jolly Roger

[The Haymaker]

Though I've yet to move beyond Tater Hater V1.69 http://www.xr65r.us/cannon, (THV2.0 will use a coaxial), I put thought also into the problem of the piston coming back to soon.

I don't think it will be an issue because it should take long enough for the pressure in the rezzie to drop down less than what the incoming air to the back of the valve can begin overrunning, for the projectile to be well on it's way into the troposphere.

I'd suggest two things, use a dump valve with plenty of flow to bleed off more than what the inrushing air can keep up with, or limit the air supply with a cannon mounted valve that you can pretty much "set and forget", it's only reason for being to limit incoming volume.

[Jolly Roger]

Yeah I've been looking around the site a bit and found clides mad semi auto which has a custom slide valve, exactly the same as a slide check valves on markers. It's a really simple 3 way valve. It allows air from supply line to resevoir when foward and when pulled back it shuts off the supply pressure and exhausts resevoir pressure into the atmosphere. It's brilliant! I think I might either make my own out of some sort of alloy aluminium or just get a slide check valve off a paintball site. (Not sure about there flow rate though cause their only like 1/8 ports...)