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Will this work?

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: Brian the brain » Thu May 06, 2010 4:23 pm

The " no pressure here" area seems to be a little large.
Move pilot volume and wasted gas..

Sure, it needs the vertical channel for the piston movement, but the side channel should be about thalf that size..

1/4" should suffice.
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Unread postAuthor: POLAND_SPUD » Thu May 06, 2010 5:07 pm

uhmm yeah but you can't tap air.... it would be best if he removed the BV port completely and used the one at the bottom for piloting...

if you do that you can also reduce the size of the block by about 25%
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Unread postAuthor: Marffy » Thu May 06, 2010 6:58 pm

Why wouldn't it? It looks like a "T" piston with a 90 elbow connected to a barrel?
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Unread postAuthor: POLAND_SPUD » Thu May 06, 2010 7:29 pm

I don't think I understand what you are trying to say ??
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Unread postAuthor: Gun Freak » Thu May 06, 2010 7:44 pm

POLAND_SPUD wrote:I don't think I understand what you are trying to say ??


he's saying it's just like a normal barrel sealer, which are proven to work...
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Unread postAuthor: POLAND_SPUD » Thu May 06, 2010 7:49 pm

yeah but that was discussed on the first page.... and the consensus was that there has to be surface area differential for it to work...

for me the real question is why there is an extra port for piloting it if he can use the one that is plugged in...
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Unread postAuthor: Gun Freak » Thu May 06, 2010 7:55 pm

POLAND_SPUD wrote:for me the real question is why there is an extra port for piloting it if he can use the one that is plugged in...


Yeah I don't get it either... I think he designed it so the trigger would be in the right place but it could easily be made more powerful by taking out the plug and replacing it with the pilot.
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Unread postAuthor: iknowmy3tables » Thu May 06, 2010 10:00 pm

could you clarify your ultimate objectives for your design? you claim you want it as compact as possible, but there's definitely more to it than that, like I imagine you have some general dimensions in mind for fitting into the stock of the bullpup, am I right?. and the placement of the pilot probably has it's purpose too

The engineering design process calls for identifying the need of the client (in this case yourself), but the need is often different from what we initially think, I recommend thinking of what you want for the project, then breaking that "want" down a step by step to a more basic "wants", for example "I want a marble minigun" -->"I want a automatic marble gun"-->"I want a pneumatic gun with a high rate of fire" keep doing that until it becomes irrelevant to engineering like "I want to own a device that helps me compensate for my shortcoming in manliness"
breaking down the need should help you isolate the want or need for designing purposes

Isolate your need/want/objective for this piston design and tell us so maybe we can help give you some ideas
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Unread postAuthor: Crna Legija » Thu May 06, 2010 10:44 pm

dosent the piston need to be bigger than the seal? so that air can push down it back if its the same ill wil not fire
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Unread postAuthor: Jack_Hogg » Fri May 07, 2010 8:57 am

I want a 10mm short sniper rifle for homemade lead slugs. I want a bullpup design to get it short, ergonomic, and to keep the power and accuracy. That's my main goal. I might change the design to like you guys said. Instead of piloting from the side, I will make it pilot on the bottom where it's plugged. The reason why I wanted to pilot it from the side was mainly becouse I wanted to make it look clean and I thought it would be a nice design. But I decided to make it pilot from the bottom. No problems with springs or what so ever. I do have a question though.. I wanted a spring assisted ballvalve to keep the preformance, but I think the lever of the ballvalve will be in the way when you hold it to your shoulders. So my question is; How can I pilot the best way, when the main system is in the back and the pistol grip in is the middle of the gun. 1. A small 1/2" qev with a small copper pipe to a ballvalve in the handle?
And how should you connect it to remain looks?

Thanks for the help guys.
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Unread postAuthor: Crna Legija » Fri May 07, 2010 9:19 am

i think that you could use a 1/4 push button valve like the one BTB made
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Unread postAuthor: Gippeto » Fri May 07, 2010 9:20 am

I would suggest a differential spool valve (BTB push button) actuated by a sliding hammer. (striker for the fussy)

This would allow the use of a trigger and sear arrangement with more foreward placement, resulting in better ergos, and benefitting from greater consistancy and tune-ability.

Give some careful thought as to "what" you're going to do with the high pressure discharge from the pilot. It's MORE than enough to cause injury in and of itself.


Edit....Bugger it..beaten to the punch. :lol:
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Unread postAuthor: POLAND_SPUD » Fri May 07, 2010 10:10 am

IIRC copperhead prime had no QEV to assist piloting... not that I am saying you don't need one but 1/2" might be a bit too large...
1/4" or 3/8" would probably be enough...

ideally you would like one with male threads as that will help to keep dead volume down


Another idea is to use a differential spool valve (BTB push button) but attach a wire from bike brakes to it in order to 'trigger' it...
in this way, you could place the trigger where you want it to be but the valve can be threaded in directly at the pilot port of the main valve

I've never tested it but it seems like a good idea
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Unread postAuthor: Gun Freak » Fri May 07, 2010 4:14 pm

If you were going to use the 1/2 qev to pilot it you might as well replace your piston valve with the qev :P
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Unread postAuthor: iknowmy3tables » Sat May 08, 2010 5:06 pm

I think using a QEV or making a piston valve with real pipe fittings would better utilize the space in the stock, and then to get the overall shape you wanted you could use some polymorph
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