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Piston Exhaust Valve Setup

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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Piston Exhaust Valve Setup

Unread postAuthor: MountainousDew » Fri Apr 17, 2009 6:30 pm

Hello,
I have one last question before I put my gun together, and of coarse shoot her.
Below, I have a basic design of how my gun will be put together, I haven't seen this setup before and I didn't how if it would even work. The piston is barrel sealing, the fill valve is a shrader valve, and the exhaust valve is a sprinkler valve. (And there will be several holes/cuts in the stock to release the air)
But, I didn't know if the air will be able to escape quick enough for the piston to open correctly, so will it?
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Unread postAuthor: daniel323 » Fri Apr 17, 2009 6:40 pm

depends on the size of holes you drill..

its possible if they are big enough
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Unread postAuthor: SubsonicSpud » Fri Apr 17, 2009 7:30 pm

Even if there were no holes in the stock, it would probably fire, as long as there is a large enough volume in the stock. But for best performance you are going to want to have a hole area equal or greater than the sprinkler valve porting area

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Re: Piston Exhaust Valve Setup

Unread postAuthor: Technician1002 » Fri Apr 17, 2009 7:34 pm

MountainousDew wrote:Hello,

But, I didn't know if the air will be able to escape quick enough for the piston to open correctly, so will it?


Will it or won't it depends on several factors. In short the pressure behind the piston needs to be low enough to unbalance it from the pressure holding it against the barrel and overcome friction. If the piston has a high leak rate (bleed port), the pressure may not drop enough to meet the conditions required for it to open.

Without info on the piston, how it seals, how much the stock can vent, what the sealing surface (orifice) size and piston OD, and the amount of moving friction, it is hard to predict the behavior.
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Unread postAuthor: MrCrowley » Fri Apr 17, 2009 7:46 pm

I've seen something similar on a co-axial cannon. It worked fine but he didn't use any end caps on the stock, so there was plenty of flow for the air to escape.
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Unread postAuthor: c11man » Fri Apr 17, 2009 8:42 pm

looks like it would work nicely .

only suggestion i would have is to make sure not to drill any holes in the top so it doesnt blow air into you face :(
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Unread postAuthor: MountainousDew » Fri Apr 17, 2009 8:50 pm

Thanks guys for the input... Sorry I didn't reply earlier, but I went to Lowes to get an estimate on the gun and it is going to be about forty dollars. I'm very excited, and will start working on it tomorrow.
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Unread postAuthor: jmeyer1022 » Sat Apr 18, 2009 1:58 pm

Here is a slight modification for you, Keeps your design the same except one thing allowing the exhaust without drilling holes, to keep a cleaner look.

Image

The red is where the pilot would exhaust through, Instead of just doing straight pipe on that part put a tee and don't cap the vertical portion so the air will exhaust there. Just a suggestion do with it as you please.
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Unread postAuthor: Carlman » Sat Apr 18, 2009 2:05 pm

I would think that a well built valve will function just fine with a sealed stock. If you were to keep it sealed you would not hear the ssssssbang as per normal, rather just the bang.
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Unread postAuthor: Technician1002 » Sat Apr 18, 2009 2:11 pm

Carlman wrote:I would think that a well built valve will function just fine with a sealed stock. If you were to keep it sealed you would not hear the ssssssbang as per normal, rather just the bang.


Quick dump valves have the bang without the sssssssssss.
:D
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Unread postAuthor: Carlman » Sat Apr 18, 2009 2:19 pm

Technician1002 wrote:
Carlman wrote:I would think that a well built valve will function just fine with a sealed stock. If you were to keep it sealed you would not hear the ssssssbang as per normal, rather just the bang.


Quick dump valves have the bang without the sssssssssss.
:D


Man you like self promotion dont you? lol
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 18, 2009 2:26 pm

Carlman wrote:Man you like self promotion dont you? lol


In all fairness his design is more efficient than any exhaust piloted valve will ever be, so he has a point ;)
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Unread postAuthor: Carlman » Sat Apr 18, 2009 2:29 pm

jackssmirkingrevenge wrote:In all fairness his design is more efficient than any exhaust piloted valve will ever be, so he has a point ;)


getting a tad old though
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Unread postAuthor: Technician1002 » Sat Apr 18, 2009 3:20 pm

Carlman wrote:
jackssmirkingrevenge wrote:In all fairness his design is more efficient than any exhaust piloted valve will ever be, so he has a point ;)


Jackssmirkingrevenge, Thanks for the kind word.

getting a tad old though


Sorry, I have lightened up some. Most of my recent posts don't mention it.
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