SpudFiles

i have just made a pneuamtic piston valve cannon similar to this:
http://www.spudfiles.com/forums/viewtopic.php?t=252

it's actuated by a blowgun. the problem is,the piston wont actuate. i pump up the canmber to 60ps1 to test it,pull the blowgun,and all the air just vents out the blowgun. im wondering if the piston is too small;it slides in a 1'14 inch chamber and seals on a 3/4 inch barrel. the piston slides sweet enough,so i dont think that friction is the problem. any ideas?

sounds like your only pressureing the valve side of the cannon, do you have a little hole in your piston to fill the chambers? if air was leaking through some where you would hear it

jrrdw's suggestion is probably the first thing to check.

Second thing could be the kinda the opposite problem, you are pressurizing both side of the piston, but, have too much return flow, from the air chamber back to behind the piston. When you actuate the blowgun, the pressure differential isn't great enough, due to return leakage, causing the piston not to budge.

I had this happen on my first piston valve. You'd think that a small pressure diffierential would cause the piston to move backward, but if the flow out of the blowgun is being compensated by "leak back" from the air chamber, the piston won't have enough of a pressure difference to cuase it to actuate.

if this is the case, try a "poor man's" check valve, which is usually a flap of rubber or gasket material, or, plug the air passage in the piston, and drill a smaller hole.

Let us know what you find.

i pressurise from the chamber side,and the piston seals,so its not the first suggestion. i think that SkunkWerX's suggestion would be closer,there does seem to be alot of leak-through. there isnt actually a hole in the piston,i made it so air could leak around it,ill remake the piston,its only a block of wood anyway. what were you talking about a "poor man's valve"? it sounds interesting

what is a good material to make the piston out of? taking into consideration that the chamber is only 1.14 inch dia.

This happened to me when I installed a blowgun, so I just went back to using a turn ball valve. Not quite so cool but it's functional.

the moog wrote:This happened to me when I installed a blowgun, so I just went back to using a turn ball valve. Not quite so cool but it's functional.

definitely not as cool,not as fast-opening. i want to upgrade. plus,i stuffed up my ball valve,i stripped the thread that holds the handle on. i thought of that as a sign to change

find a piece of rubber/stiff, or use a piece of tupper ware lid, and on the chamber side of valve cover the little hole by glueing one side down 'poor mans check valve' ack's like a flapper

i don't think it matters what side you fill from, air leaking around piston will cause problems

make a new piston from pvc end cap, sand down outside of cap untill it fust fits snuggly but slides freely, use a piece of inner tube in the center to seal against barrel

spud wiki has good plans and pics to guide you, look under valves on left side of wiki home page, good luck

jrrdw wrote:find a piece of rubber/stiff, or use a piece of tupper ware lid, and on the chamber side of valve cover the little hole by glueing one side down 'poor mans check valve' ack's like a flapper

i don't think it matters what side you fill from, air leaking around piston will cause problems

make a new piston from pvc end cap, sand down outside of cap untill it fust fits snuggly but slides freely, use a piece of inner tube in the center to seal against barrel

spud wiki has good plans and pics to guide you, look under valves on left side of wiki home page, good luck

sweet mate,will do 8) thanks for the help

make sure you let us/me know how/what you do to fix your cannon, any problems dureing the makeing, and any fine tuneing tricks to make it work better

this tread would be good lesson in insturction manual

*ATTENTION* i wont be doing any more on the cannon for a couple of weeks,i broke my foot pump and my wage is tied up until then. still,keep the ideas rolling,please

how many pumps does it take to pressureize your chamber?

no wonder your foot broke, it's all worn out from pumping up your cannon-lol

man save your foot and time, get a 12 volt tire inflater - dirt cheep were ever you go, ebay/wal mart/hardware stores ect.....

i seen them on ebay for 1 penny, 5 dollar shipping, thats probly cheeper then foot pump

they also make them rechargable now so you don't have to drag that peskee car around-hehehe

get well soon dude !!!!!!