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Piston Valve Design

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: MrCrowley » Mon Nov 26, 2007 2:45 am

Yeah agreed.

In the video you can hear all this air hissing out after the projectile has left the barrel, this is due to a few things:

1) Sprinkler valve has little flow for such large amounts of air

2) The bends are dead space

3) Short barrel.
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Unread postAuthor: Lftndbt » Mon Nov 26, 2007 8:18 am

Following JSR's post.. On Chamber volume..

Might be a stupid suggestion but...
Why not add two ball valves, making the two chamber's independent...
Two standard shot's, or open both valve's and get one big shot..
You should have enough volume, to get two good shots out of those chambers.

:)
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Unread postAuthor: daberno123 » Mon Nov 26, 2007 4:59 pm

jackssmirkingrevenge
Thanks I think I will change the position of the valve to where you suggested but probably not until I get replacements for my dwv fittings

Lftndbt
Thats a good idea and I like the sound of two shots without having to refill the chamber

Overall I don't think that I will build this valve, I'll probably just use a regular piston design. I was thinking about using Mr. Crowley's design for a 2" piston valve. The main reason for not building the valve was the excessive use of sheet pvc was not feasible. I was wondering if I could put 2 piston valves on this instead of one. I'm not sure if that would work or not, I haven't seen any guns on here with that design. This is what it would look like with 2 piston valves. Not sure if both would seal though if I filled the tank up through 1 quick disconnect valve.

Below is a very rough sketch of what it would look like with 2 valves
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2007 11:26 pm

While you seem to enjoy dual setups, I don't think it's worth the effort in terms of performance to make two piston valves, one is more than enough if you make it well - however, as I said earlier, no one's stopping yur putting 4 valves if you so desire.
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Unread postAuthor: psycix » Tue Nov 27, 2007 10:33 am

jackssmirkingrevenge wrote:While you seem to enjoy dual setups, I don't think it's worth the effort in terms of performance to make two piston valves, one is more than enough if you make it well - however, as I said earlier, no one's stopping yur putting 4 valves if you so desire.


Then make a piston valve instead.
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Unread postAuthor: Ragnarok » Tue Nov 27, 2007 10:48 am

JSR is right.

Dual valves should only be done when you need more flow but can't actually make a bigger valve. One big valve has several advantages over two small ones- less dead space, less turns, etc.
It has some disadvantages too, larger valves are a little harder to construct and have to have a larger total pilot volume, but I'd go for one, not two.

Dual valves has been done, but they're using pre-manufactured valves in a set size. I even think 4 sprinkler valves was done once, but that was a little spurious IMHO.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 27, 2007 12:00 pm

Technically speaking, dual valves doubles the rate of flow increase, and would be equivalent to a faster opening valve, but just how much difference that would make and if it would be worth the extra construction complexity is debatable.
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