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check valve

Posted: Thu Jun 22, 2006 7:40 pm
by Mini Khan
is it posible to use a check valve for a primary valve? Exuse the bad spelling.

Posted: Thu Jun 22, 2006 7:50 pm
by carlbelcher
No you can’t use a check valve as a “primary valve”. Check valves are designed to let air though only one way and there is no way the control the flow in that one direction, so you can't use them as a \"primary valve\" assuming that you’re referring to the main air valve on a pneumatic cannon. You should check out the spud wiki it has a great section on valves.

Posted: Thu Jun 22, 2006 7:55 pm
by CS
Normally no, but Ive always wanted to try a method of using them. Simply connected a bolt via a coupling nut on the threaded piston in the check. It would work like a mortar. When projectile hit bolt it would shoot projectile like a mortar.

Posted: Thu Jun 22, 2006 7:58 pm
by carlbelcher
Hey that's about the best idea I've heard all day. The only problem is that the instant the projectile left the bolt the valve would close.

Posted: Thu Jun 22, 2006 8:24 pm
by Shrimphead
I could see it working on a small cannon.

Posted: Thu Jun 22, 2006 9:10 pm
by frogy
carlbelcher wrote:Hey that's about the best idea I've heard all day. The only problem is that the instant the projectile left the bolt the valve would close.
I'm not sure that's true... Once the valve is open the piston's equalization area would be drained already so it would let all the air out, I'm not sure if you understand this because I'm tired and I forgot what you call the equalization area :D

Posted: Thu Jun 22, 2006 10:05 pm
by carlbelcher
If you look at the way check valves work the flow of water in one direction would force the valve open, but water flowing the other way would slam the valve shut. The same applies for the cannon, except the water that would normally flow to push the vales open is a projectile hitting the check plate, ball, or door. So when the projectile hits the check plate, ball, or door it opens it monetarily just enough for the air to start flowing past the check plate, ball, or door as the air does this it forces the check plate, ball, or door closed just like water would. And that is if the projectile has enough force and or mass to push the check plate, ball, or door open against the air pressure in the chamber anyway. I included some pics of different PVC check valve for examples.

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Posted: Thu Jun 22, 2006 10:17 pm
by noname
If you had a large, fast closing check valve and a big chamber you could pretty much have a mortar.Just keep dropping stuff down and it would lose air a little bit at a time unless you ran a compressor with it. Hey that's a good idea. :D

Posted: Thu Jun 22, 2006 10:54 pm
by carlbelcher
I still think the biggest problem is forcing open the check valve against the pressure. Just think, say the check valve only has a 1 inch check plate or door and you have a chamber with 90psi in it.


pi x .5 inches = 1.57 square inches x 90psi = 141.3 pounds of force


:!: That means to force the check vale open it would take 141 POUNDS OF FORCE :!:

Posted: Thu Jun 22, 2006 11:25 pm
by Mini Khan
thanks for ruining my dream carlbelcher, but what if u had an exuast valve at the back of the chamber?

Posted: Thu Jun 22, 2006 11:36 pm
by carlbelcher
Sorry, but I don't think that wouldn't work ether because you would have exhaust all the air from the chamber to open the check valve. :(

Posted: Fri Jun 23, 2006 12:01 am
by Mini Khan
well than how bout if i put it at soo much psi it blows the valve, that would work!!!

Posted: Fri Jun 23, 2006 12:26 am
by carlbelcher
I guess that's one way to do it! LOL!

Posted: Fri Jun 23, 2006 9:45 am
by noname
And then your wasting a buttload of cash. At the local hardware store near me, the smallest check valves they have are 1/2", and just those are $7.50! I could use them in diaphram guns though. Just drill a few holes and extend the valve out the the exhaust.