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the reason why you want a good bumper in a piston valve

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Zeus » Mon Mar 21, 2011 4:22 pm

Well there's your problem.

It only needs maybe 1 1/2 inches, perhaps less.

The piston had a large runup, but it had to stop in rather a small amount of space, there's a lot of force in a piston at full speed, couple that with PVC that's brittle, even more so in low temperatures, and not much of a bumper.

I wonder if the piston could launch itself out of the piston housing into the firer?
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/sarcasm, /hyperbole
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Unread postAuthor: hollowpoint666 » Mon Mar 21, 2011 4:49 pm

Zeus wrote:Well there's your problem.

It only needs maybe 1 1/2 inches, perhaps less.

The piston had a large runup, but it had to stop in rather a small amount of space, there's a lot of force in a piston at full speed, couple that with PVC that's brittle, even more so in low temperatures, and not much of a bumper.

I wonder if the piston could launch itself out of the piston housing into the firer?


by firer do you mean operator/ the person using the cannon? then yes, the piston flew out the back and hit my house leaving a large gash in the siding, if it wasnt for the size of the cannon, requiring me to hold it from the side (it is / was 9' long) it would have hit me for sure, i was lucky it didnt smash into my hand that turned the valve
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Unread postAuthor: Crna Legija » Mon Mar 21, 2011 6:59 pm

yea that way to much travel you only need 1/4 the dia of your barrel port.
and that hole cannon looks like its made from dwv, not surprising it blow up.
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Unread postAuthor: mark.f » Mon Mar 21, 2011 7:02 pm

Ragnarok wrote:The rating is the number that says 240 psi (or whatever other pressure), never the NSF mark.


Fittings do not have a specific pressure rating stamped on them. They have the NSF and ASTM ratings. You are correct that the NSF ratings are for the type of service (drainage/waste/etc. or potable water), which more often than not corresponds with a pressure rating since potable water is delivered at pressure nearly everywhere in the continental United States. There are more NSF ratings as well.

However, the final status on pressure rated vs. non pressure rated should be taken from the ASTM marking. For solid core pressure rated SCH-40 PVC fittings, the rating is ASTM D2466.
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