modified sprinkler valve problem

[theregoesthewindow]

I have a pnuematic cannon with a modified sprinkler valve. it works okay but occasionally after cutting the potato and pushing it down the barrel we, my friend and i, will start to pressurize the cannon and the potato will slowly be pushed out of the barrel. what is happening?

also how do you fill your chamber quickly, i'm using a bike pump now

[darkpyro]

to fill your chamber quick get a compressor or co2 setup have a look in the how tos for the co2 setup and you can get a compressor that plugs into a power point from hardware stores or a smaller compressor that plugs into cars from some supermarkets and most two dollar shops.

about the potato coming out of the barrel some times when the potato is realy tight fitting when you push it down the pipe it wont let any of the air under it out so it pressurises and once the potato is down the bottom it pops back up again because al the compressed air under it dont know how to fix the problame other than to cut losser fit potatos.

hope you under stand there is probaly nothing wrong with your mod.

[CS]

If there is something wrong with your sprinkler valve you should be able to tell quite simply. Unscrew you barrel then pressurize the chamber and see if air leaks out the barrel side. DarkPyro's theorie seems to be plausable, but it would pop back up as soon as you removed pressure from the ramrod. So that makes me think that your right in your conculsion that your sprinkler is the problem. Tell us the syptoms of the leaking sprinkler valve and we might be able to help you out (that is if there is a problem with the sprinkler valve).

[nicholai]

the diagphragm probably isnt sealing completly, did you buy the valve or mod it yourself?

to fix the potato sealing problem screw your schrader valve (or quick disconnect nipple for air compressors) into a ball valve. make sure the ball valve is open when loading the potato and if you are using a schrader valve push in on the metal valve piece to make sure any pressure created by the nicely sealing spud is vented through the air hole. just dont forget to close the valve up after the chamber is pressurized!

[theregoesthewindow]

Actually when re-reading the little paper manual that came with it I found that it said something like use in pressures 15-120 psi, do you think this had anything to do with its malfunction, because it almost alwayed failed before 20 psi

[jrrdw]

yea theregoesthewindow, there has to be enough presure to seal the diaphram, useing a little white lithume greese will help make it seal faster and probly make it last a little longer/maby

as for filling it fast, yea get a ait compressor, the little 12 volt ones are only a couple bucks, you can gettum from ebay real cheep just watch shipping cost, they will fill the chamber pretty fast, work very well on bike/wheelchair tires

get some pics posted

[darkpyro]

hey speaking about leaking valves i bought a solinoed sprinkler valve that was leaking and i never used it much more than 30 psi can a normal un moded valve leek?

[jrrdw]

there can be flaws in castings, hairline cracks places you can't see but air will find them, i'm sure during testing of these valves before they leave the factory, they miss a bad one from time to time, probly only test one every 2 to 3 hundred valves made, would take to long to test them all

factory tested don't mean every single 1 any more !

[darkpyro]

okay thnxs i will try useing the valve again only at a higher psi