Piston Valve Clarification

[ElasticBandit]

Okay now before you yell at me, I understand how a piston valve works(at least I think I do), and I've done a search for this question and it hasn't been answered (to my knowledge) right.



So how do you actuate(sp) a piston valve? Rather how do you get it to open up to propell your ammo forward? Is it man powered? Do you actually pull back on the valve or what? Can it be electric?




Okay maybe I don't understand to the fullest extent how it works, but from my searches I at least know how to make it. That has to count for something.

[LGM]

You release the air behind the piston. It gets drawn back by suction.

[ElasticBandit]

oh! so you use it in conjunction with, say, a ball valve?

[LGM]

Yes. Just don't try a blowgun, it won't work.

[ElasticBandit]

what about a solenoid?

[LGM]

Definetely, go ahead.

[ElasticBandit]

Now this is a complete clarification post:



First you have your barrel with your piston valve butted up against it for an airtight seal with the piston lubricated

Second behind the Piston you have the solenoid valve(for example)

Third the Chamber is cnnected to the solenoid and when the solenoid is activated, the piston will draw back due to sucktion(sp?) and the compressed air will shoot the projectile foward.

Forth: When the solenoid is deactivated, the piston will go back to the original position, recreating the airtight seal with the barrel.





am I correct?

[LGM]

That's about it, but the piston wll only retur to that postion if it is spring loaded or is made to go back into place when the chamber is filled up behind it. And a ball valve would be a lot better for this purpose because it will work fine and is cheaper.

[ElasticBandit]

Gotcha ... does the orientation in which the piston/ball/chamber are located matter to the overall working of the gun?


By orientation I think I mean where each one is in relation to each other, obviously it has to be in the order of piston/ball/chamber.


and the piston/ball formation would have no impact on where you'd place your pressure gauge correct? AHHH what am I saying the gauge goes with the chamber and generally isn't near the valves forget it.

[LGM]

I think you have it mixed up.

I will use a coaxial cannon as an example. The barrel extends down into the chamber until it is near the end, then a piston that seals the barrel and ffits the chamber well, then the endcap in which is a fill valve and a release valve. Pressure this up, and release the air from behind, drawing the piston back.

[CS]

As I also had a hard time understanding the functioning of piston valves at first, this animation helped me better understand:

<a href="http://forums.spudtech.com/topic.asp?TO ... 65">Piston valves explained visually.</a>

From a theoretical standpoint you create a pressure difference across a mass, called a 'piston', creating motion. One state sealing passage of stored gas to the barrel, and the other releasing it. The piston is moved out of its 'sealed' state by having pressure on the 'face' of it, and releasing the pressure behind it.

[ElasticBandit]

ahhhhhh that makes alot of sense now that I understand how the piston works. and you'd have to shut the ball valve to get the piston back to the starting place(so long as the piston is spring loaded.

[SpudBlaster15]

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[squeaks]

yep, and if you really want to be fancy about all of this you can make a second, smaller piston valve to actuate the large piston and use a blow gun on a small legnth of hose to actuate the smaller one. This way you can make a trigger kind of thing instead of turning a valve.

[mark.f]

Just make sure the flow of your pilot valve is greater than the flow of air around or through your piston. In other words, if your piston allows around 60 SCFM@100PSI of air around it, then your pilot valve would have to have a little over 65 SCFM@100PSI to work well.