piston

[tape fist]

Im using a spring to push my piston against the barrel dose it matter how tightly it dose?

[sputnick]

I would imagine not, unless we are talking ALOT of pressure here, since it is being pushed back by 100 pounds X the area of your piston, but why do you need a spring unless it isn't filled from behind...

[ralphd]

I'm new at this but I don't think so. From the designs that I've look to model mine the pressure of the air will hold the piston against the barrel but make sure the spring isn't too strong that it delays or even stop the piston from sliding open when firing. By the way, why are you doing this?

[tape fist]

im filling from the bottom so i need a spring.

[sputnick]

Well, what's wrong with trial and error... just make the piston accessible, then if one spring isn't doing it, just try a different strength one.

[tape fist]

I would imagine not, unless we are talking ALOT of pressure here, since it is being pushed back by 100 pounds X the area of your piston, but why do you need a spring unless it isn't filled from behind...

thank you i might shorten the spring because it might be to strong.

[MrCrowley]

Im using a spring to push my piston against the barrel dose it matter how tightly it dose?

Yes. Too soft and the air pressure from the chamber when filling will force the piston back and all the air will go out the barrel.

Too strong and when you go to fire the cannon, the piston might 'bounce', sealing prematurely and leaving air pressure in the chamber or if it doesn't seal completely, it might just limit flow.

Use your head and think about these things, if you know about the physics behind a piston valve, these things should be clear to you.

[tghhs]

Yeah i duno, just doesn't seen like it's worth the hassel, just another thing to go wrong. Does it have to be pumped brom the bottom of the "T"?

If it does just run some brakeline or something from ur pilot area to where u want it to be pumped, then just glue ur shrader or whatever valve u want in the end, you'd have to trim-down the shrader though.

But thats just another seal to go wrong.

it'd far easier and less time consuming to just fill it from the pilot, then u'll be lunching stuff in no time

[inonickname]

Piston valves explained visually

Scroll down to barrel sealing tee. That should help you.

[MrCrowley]

Piston valves explained visually

Scroll down to barrel sealing tee. That should help you.

How? Those animations all show pilot side filling with no springs...what's that got to do with what 'tape fist' asked?

[inonickname]

Piston valves explained visually

Scroll down to barrel sealing tee. That should help you.

How? Those animations all show pilot side filling with no springs...what's that got to do with what 'tape fist' asked?

Does it have to be pumped brom the bottom of the "T"?

I think I might have misread his question..

[tghhs]

Piston valves explained visually

Scroll down to barrel sealing tee. That should help you.

How? Those animations all show pilot side filling with no springs...what's that got to do with what 'tape fist' asked?

Does it have to be pumped brom the bottom of the "T"?

I think I might have misread his question..

haha lol, this is really confusing now, i ment for the purpose of the gun, do u have to pump into the chamber (the bottom of the T) and if so just run a hose from the pilot to where u need it to be pumped, not does the valve need to be pumped from the chamber.

i think this clears up cunfusion, lol Tape Fist would have built a connon by now anyway

[psycix]

Most people simply pump into the pilot volume. Air goes past the piston into the chamber. This does not require a spring.

If you NEED to fill from the chamber for some reason, then you need a piston without o-rings, and a spring to overcome the tiny pressure differental when you start pumping.
If there is already some pressure inside, you dont need the spring anymore, as the piston is pushed against the barrel by the pressure already.
The sthrength of the spring is experimental and depends on the fit of the piston and how fast you fill.

[tape fist]

haha lol, this is really confusing now, i ment for the purpose of the gun, do u have to pump into the chamber (the bottom of the T) and if so just run a hose from the pilot to where u need it to be pumped, not does the valve need to be pumped from the chamber.

i think this clears up cunfusion, lol Tape Fist would have built a connon by now anyway

Ive decided to read up more my pneumatic cannon is great right now but i just wanted to see other options so that when i build one out of copper i can make it more powerful were as using a sprinkler valve would limit me to 125 psi.
thanks for the diagrams they really helped