Piston valves explained visually

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Postby PCGUY » Fri Apr 28, 2006 7:34 pm

<font color="green">Originally posted by Clide, but stupid Snitz archived it</font>

Well I made this flash animation in hopes to explain piston valves for the most part. Let me know if this helps anyone figure them out. Those who already know, please point out if you spot something wrong.

<hr>
<font size =+2><b>Phase Explainations<br></font><font size =+1>Applies to all Models</b></font>
You may need to watch it several times because there are many things going on at once. This assumes you know the relationship between pressure, surface area, and force (pressure * surface area = force)

<b>Phase 0:</b> Basically just the gun in its pre-use state. No pressure in the gun.
<b>Phase 1:</b> An air source is connected behind the piston. Air enters the pilot chamber and the pressure pushes the piston against the rear of the barrel or chamber port.
<b>Phase 2:</b> Air continues to flow through the input and leaks around the outside of the piston or through an equalization hole into the main chamber. Once desired pressure is reached, the input flow is cut off and the gun is ready to fire.
<b>Phase 3:</b> The exhaust valve is opened and the pressure begins to fall in the pilot chamber. The exhaust must exhaust faster than the equilization hole can leak air back into the pilot. Once the force pressing on the back of the piston falls below the force acting on the front of the piston, it begins to slide back. Suddenly there is more surface area exposed on the front of the piston, and the jump in force slams the piston back leaving an opening for air to flow into the barrel to accelerate the projectile.

The exhaust valve is closed and a new projectile loaded. The gun is then back to it's original condition, ready for the cycle to repeat.

The main thing to notice between the different types are the forces caused by pressure. Of course forces could be changed by changing the changing the piston/sealing port diameter, but in the general senario like the one shown, with a constant barrel diameter between all types and a tee slightly larger than the port, the barrel sealing valve will have the same forces as coaxial in the closed position. Barrel sealing will have the highest opening force, coaxial will be in the middle, and chamber sealing will have both a low closing force and a low opening force.
<hr>
<font size=+2><b>Coaxial Piston Valve</b></font>
<embed src="http://gbcannon.com/flash/coax.swf" quality="high" bgcolor="#ffffff" width="550" height="350" name="coax" align="middle" allow$criptAccess="sameDomain" type="application/x-shockwave-flash">


<hr>
<font size=+2><b>Barrel Sealing Tee Valve</b></font>
<embed src="http://gbcannon.com/flash/barrelseal.swf" quality="high" bgcolor="#ffffff" width="550" height="350" name="barrelseal" align="middle" allow$criptAccess="sameDomain" type="application/x-shockwave-flash">


<hr>
<font size=+2><b>Chamber Sealing Tee Valve</b></font>
<embed src="http://gbcannon.com/flash/chamberseal.swf" quality="high" bgcolor="#ffffff" width="550" height="350" name="chamberseal" align="middle" allow$criptAccess="sameDomain" type="application/x-shockwave-flash">


<hr>

Update: Now includes a control panel with play, pause, skip, frame by frame, and slow motion (took forever to figure out).

Update 2: Added labels for both the controls(mouse over) and the gun parts. You may need to Ctrl+F5 to see the updated flash if you viewed this page before. Also added a barrel sealing tee flash and tuned down the forces on the Coaxial flash to be more accurate compaired to the Barrel Sealing Tee flash.

Update 3: Added Chamber Sealing Tee flash, corrected minor bug with the forces on Barrel Sealing Tee flash, and fixed incorrect force displayed in the closed positon of Coaxial flash.
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Postby jmoney720 » Tue Jun 13, 2006 8:54 pm

does anyone know how joel's supah valve works?
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Postby SpudMonster » Tue Jun 13, 2006 8:58 pm

It is a chamber sealing tee valve. Not much is known about his valve, and those who do know about it don't say much about the valve out of respect for him.
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Postby Navigator7 » Wed Jun 14, 2006 1:41 am

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by jmoney720
[br]does anyone know how joel's supah valve works?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I bought two.
They work perfect.
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Postby Navigator7 » Wed Jun 14, 2006 1:54 am

PCGuy,
Nice job!
Not criticizing ....just splitting hairs....
Incoming air does not necessarily have to come from behind the piston to make the system work.

The equalization hole will fill the area behind the piston and it will seal just fine.

However!!!! You also answered something that stumped me before....as I was able to make my cannon fire by rapidly filling it from a nitrogen tank.
I think I was able to fill the camber faster than the equalization hole would allow filling...causing the cannon to fire weakly...as in very low pressure.
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Postby clide » Wed Jun 14, 2006 8:28 pm

I made it, PCGUY reposted because the forums archived it.

I only mentioned being filled from behind just because that is the system in it's simpilist form. Easiest to explain, learn and build.
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Postby Navigator7 » Thu Jun 15, 2006 12:55 am

PCGUY just asked for comments...I gave one.

Nice service you performed!

Ever have misfires like what I was talking about?
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Postby clide » Thu Jun 15, 2006 6:53 pm

I asked for comments :p and I do appreciate them, should help people understand. If I ever get around to it I will be putting these on a web page and I'll have a page to explain more advanced details of piston valves, since you mentioned it, filling from the chamber will be one of the things I need to put in there.

I haven't had a misfire like that, but I don't have any piston valves that fill from the chamber side. It does make sense though that filling too fast could cause low pressure firing in a valve like the Supah.
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Postby Navigator7 » Thu Jun 15, 2006 9:12 pm

Clide...are there any discussions to the size ratio between the backside of the piston and barrel or chamber size?

There is all the talk about chamber barrel ratio but I never see much in the way of piston size ratios. If you get my drift?

In other words..if a guy goes out to build a piston valve....he just may build a valve that will never work.
I've never seen much discussion on that aspect.
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Postby clide » Thu Jun 15, 2006 10:23 pm

It's brought up every now and then.

Basically most valves will work as long as it isn't taken to an extreme.

A barrel sealing valve responds oppositely to changes than a chamber sealing.

In a barrel sealing, making the sealing port closer in diameter to the piston should increase opening speed up until it won't start moving back well initially, not quite sure where that point is, or even if it exists. That's one of the many things I've been meaning to test.

In a chamber sealing, making the sealing port closer in diameter to the piston should decrease opening speed. If you are keeping the piston size fixed then there is probably a point at which the increase in flow you get from increasing the port size is not a benefit because of the decrease in opening speed, this point would depend on many things about the gun. I may try to model something in GGDT to see what it has to say about it.
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