SpudFiles

OK please tell me if this idea is incredibly stupid or something, but here it is. The cannon I am designing will use a pneumatically actuated sprinkler valve, and to my understanding all that is needed is a press of the button to set it off. This seems a little unsafe to me. So I thought about putting a ball valve immediately after the main valve to act as a safety. Until the gun is ready to be fired it would remained closed. My question is- If it did go off while the safety was on, would the ball valve be able to take the impact of the air? Thanks if you can help.

yes, its not like releasing the air makes it more psi, and ppl use ballvales as triggers, so they can take the pressure inside a chamber.

Well my thought was its not the pressure of the air, it's the actual impact of the air. Do you understand what I mean? Like the air in the chamber is stagnant until the valve is opened, but in this case the air would travel several inches very quickly and slam into the ball valve.

Yea, but you make it sound much worse than it actually is. This equalising of pressure dosen't actually add any PSI or force, whatever you want to call it. I don't know the reasons why but it just is that way. By the way, even if this "rushing of air" added tons of PSI, ball valves are built to take it, no worries there.

you can just put a safety switch into the sprinkler valve electronic components, or use a missile launch style button. http://www.dse.com.au/cgi-bin/dse.store ... View/P7691
anyway, with a safety switch you can't stuff up, unless you forget to use it. scared the shit out of me when i did it and yeh the ball valve will be fine in that situation..
goodluck!

OK thanks everyone. And Julz the reason I cant use an electric safety is because it is a pneumatic actuation- No electronics.

Julz, most people use pneumatic actuation because it is both cheaper, and more powerful, it opens about 2X as fast as electronic actuation.
Spencer, the ball valve will be fine, people use them on hybrids which instantly create hundreds of PSI

OK awesome thanks. I have another question actually. Its hard to explain but here it goes. If I put a cross peice after the main chamber and before the valve (1"), would it slow down the air flow at all? It seems to me that it would restrict air movement more than just having it straight all the way down. I ask because if I did that I could use fittings to attach the fill valve and pressure gauge as opposded to drilling new holes.
Also, looking at cannons on this site I see many mentions of how chambers are all double thick, which seems to be a good idea. How is this accomplished on the chamber? A coupler over it between the endcap and bushing?

that should work, i dont know y i didnt think of it, good idea i'll try it

about how the electric valves open slowly. if i made the holes in the solenoid bigger than they are now, would that allow the air to escape faster and hence the valve open faster?
also does the volume of the pressure chamber effect the max psi? in my head it makes sense for it to get harder to pump but it still should get higher right? this may be because i have a foot pump with only a medium sized chamber cos i don't like the 12v compressors.

Spencer: i think that double thickness is just done with the next size up of pipe and the gap b/t the two is filed with foam. i may be wrong but that is how i see it.
---Julz

By double thick they mean they tap their holes where there are 2 layers of plastic, that being the pipe under and endcap, so the hole is drilled through both the endcap and the pipe under it.

No I mean the entire chamber is two layers thick. Like this cannon if I can find the link... http://www.spudfiles.com/forums/viewtopic.php?t=118
I think I was right though. Just the pipe regularly used and the a coupler, followed by more pipe and then the cap. Would this work for say a 4 or 5 foot chamber if I just continued with the couplers?