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Piston Valves Explained Visually

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: James Pate » Mon May 21, 2007 6:06 pm

Thanks man that was a big help. now to make one. :?
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Unread postAuthor: repoman » Tue May 22, 2007 4:49 am

Ok, I've searched and read as much as I could before asking this question....

Is the key to a successful barrel sealer having a little bit of space on the sealing face that is the same pressure asthe chamber/pilot area?

The reason I ask is that I made a valve and the sealing face was flush against the barrel with no part of the sealing face exposed to any pressure. (beyond that that's in the barrel) Thing didn't work. I didn't really expect it to work great, it was a proof of concept, but it didn't work at all. All of it went out the pilot.

Ever since I've found this site I've been obsessed and I think if I can make a good looking and great preforming cannon I can slow down or walk away or something. That's the plan anyway. GF doesn't like guns and she'll be back in a couple weeks :/
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Unread postAuthor: MrCrowley » Tue May 22, 2007 5:24 am

You need the sealing face to have a larger diameter then that of the barrel for a Barrel sealer to work.
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Unread postAuthor: jackssmirkingrevenge » Tue May 22, 2007 5:36 am

repoman wrote:GF doesn't like guns and she'll be back in a couple weeks :/


guns? what guns? These are pneumatic launchers :wink:
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Unread postAuthor: repoman » Tue May 22, 2007 5:37 am

Thanks MrCrowley! That is the only way I could make sense of it in my head. Back to the drawing board.
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Unread postAuthor: e1337 » Tue May 29, 2007 3:45 pm

I understand everything except the equalization hole. is it just a hole where the piston meets the chamber? Please help.
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Unread postAuthor: clide » Tue May 29, 2007 4:55 pm

In most pistons (barrel sealing and coaxials) it is usually just the lack of a seal between the piston and the pipe that it slides in. Unless you are using o-rings then you usually don't have to add a hole or anything.
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Unread postAuthor: pyromanic13 » Tue May 29, 2007 5:03 pm

just out of curiosity clide, how old are you? you're one freakin awesome engineer!
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Unread postAuthor: clide » Tue May 29, 2007 5:10 pm

Thanks, I'm 21, two years to go before I am an actual engineer.
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Unread postAuthor: Flying_Salt » Tue May 29, 2007 5:41 pm

Clide, if I was a woman I would throw my body at you and let you have me as you please. But I'm just Flying Salt, so I'll just say thank you.
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Unread postAuthor: squad-coq » Sun Jun 03, 2007 3:51 am

Cool pictures, thanks, because i think you are the only one on the net with such clear pictures

But can you please make a picture of the Barrel Sealing Tee Valve only? so explain the 3 exits

when i look to it i see that the tee parts to the QEV

1(exist of 2 valve's and a piston)

2(or are this valve's blow guns?)

is this right?

3(but you can do it to with one valve!

look to this gun

http://www.spudfiles.com/forums/copperh ... t6013.html

or not??)

:idea:
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Unread postAuthor: clide » Sun Jun 03, 2007 5:47 pm

Well...that's fascinating Flying_Salt...the thanks will be sufficient.

squad, I don't completely understand your question, but I'll answer it the best I can.

You do need a fill valve and an exhaust valve, but these valves can be pretty much any kind of valve.

In the gun you linked to the main valve is a QEV, but it works pretty much just like a barrel sealing tee valve. The fill valve is a presta valve which is a kind of tire fill valve. It lets air in when you hook up an air source, but not out. The exhaust valve is the blowgun he has in the handle.

You can do it with one valve, but it has to be a 3-way valve, like on this gun http://www.spudfiles.com/forums/semi-auto-t160.html
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Unread postAuthor: chartreusesnot » Wed Jun 06, 2007 7:17 pm

Thanks, these are very clear, but the only part I dont understand is why the piston is forced back in barrelsealing ones. The pressure is coming perpendicular to the range of movement for the piston, so why would it move? *ignore the asterisks
-----------
>|piston|>>===Barrel
----^-----
**|^|
**|^|Chamber force
**|^|
**|^|
**|^------------------|
**---------------------|
oh... and which of those three piston valves (barrel sealing, chamber sealing, and coaxial) would be the most efficient in terms of performance and ease of contruction?
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Unread postAuthor: clide » Thu Jun 07, 2007 1:00 am

Pressure acts equally in all directions, and the fact that the sealing face is smaller than the piston gives the pressure an area to push on when the pilot pressure falls.
The only thing that matters as far as what direction the air is coming from is the inertia of the air once it gets moving. I'm not sure how much of an effect it would have, but I don't think it would be much since the air is usually moving fairly slowly as the valve is first opening.

It can be changed by changing dimensions, but in general barrel sealing tee valves are best performance, followed by coaxial then chamber sealing tee valves. Coaxials are easiest to build followed closely by barrel sealing tee valves and chamber sealing tee valves bringing up the rear again because of the need for o-rings.

Although in most cases the performance difference isn't enough to be a huge deal. I would suggest building whichever valve best suits the configuration you want for your gun.
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Unread postAuthor: chartreusesnot » Sun Jun 10, 2007 10:05 am

On BCarms, they sell these things called "mauler valves" are these like the piston valves? Do they work better or worse? and how expensive is it to make a piston valve? Barrelsealing valves don't need o-rings because air needs to get by the piston right?
thanks
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