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Quick Dump Valve

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: Hotwired » Sun May 10, 2009 5:06 pm

The right hand side is what is referred to as a throttle system to limit flow to a preset level, seemed to be with the intent of reducing shock on the projectile.

Since the Avalauncher fires cans of explosive with a blasting cap strapped on to the nose I can understand being cautious about that bit.

Still, it's not an ideal layout for what we'd want, the flow throttling device means the barrel doesn't reach down inside the chamber so there has to be a long piston and extra overall length plus weight.

On it's plus sides it does have a more definite valve opening time as opposed to varying a little with weight of projectile then if you chuck out the throttle system it also means less dead space between projectile and valve.

More things to throw into the blender of imagination.

I quite like the fact that the piston is on the same axis as the barrel and for that matter that the barrel can be the same pipe the piston is in.

Simplifies things somewhat.


About paintball guns using the balanced spool valve method, they also use pneumatic force to actuate the dump system: http://www.zdspb.com/tech/misc/anim_spool.html

The balanced spool valves are at the bottom.
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Unread postAuthor: jeepkahn » Sun May 10, 2009 8:47 pm

Hotwired wrote:.

Since the Avalauncher fires cans of explosive with a blasting cap strapped on to the nose I can understand being cautious about that bit.

.


Actually the shells use a delayed fuse that is started when the projectile leaves the barrel(basically it uses a flat "sabot" to seal the back of the shell and upon exit the drag of the sabot "pulls the trigger" to start the fuse) because when firing into a many feet deep snowbank, there isn't enough "impact" to set it off...
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Unread postAuthor: Technician1002 » Mon May 11, 2009 12:01 am

Hotwired wrote:I quite like the fact that the piston is on the same axis as the barrel and for that matter that the barrel can be the same pipe the piston is in.

Simplifies things somewhat.



My first cannon using this valve did use the same pipe for the barrel and valve. The valve was located at the breech end of the chamber for a longer barrel in a shorter package. It is documented here;
http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html
For those who already saw it, it's the ABS test cannon.

I edited this page on piston valves to include QEV and QDV valves in the wiki. I still need to do a spell check and other tweaks, but it's a start. Tell me what you think.
http://www.spudfiles.com/spud_wiki/index.php/Piston_valve#Barrel_sealing_valve
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Unread postAuthor: Hubb » Tue Sep 01, 2009 3:33 pm

I think I finally figured out why this type of valve has intrigued me so much. It is because this is what I was trying to do a while back. I just couldn't get it down right. But, thanks to Tech, I have since been able to accomplish this.

What I was trying to do is to put a spool type valve in a tee and have it function very similar to a piston valve, while still being more efficient, easier to maintain and operate, and simple to build.
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Hubb QDV.JPG
Here is a sketch of the valve I was trying to put together. Once it is built, I may even contribute it to ya, Tech.....
Hubb QDV.JPG (22.17 KiB) Viewed 2121 times
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Unread postAuthor: spudtyrrant » Tue Sep 01, 2009 3:42 pm

i see a problem with that design hubb where are you going to find a spring strong enough to hold that piston closed. techs works because the air pressure is pushing the side and therefore the valve is neutral with your design the piston is being pushed back by large amounts of air pressure and i don't think it will work
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Unread postAuthor: Hubb » Tue Sep 01, 2009 3:48 pm

I do see the concern, but that above is just a rough sketch. When time permits, I can draw up a better scaled diagram, which should all but eliminate that problem you described (I supposed I shouldn't have exaggerated it that much, huh?)

Another thought I have, is to eliminate the rod altogether and add a sear.....
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Unread postAuthor: dewey-1 » Tue Sep 01, 2009 6:12 pm

Hubb wrote:I think I finally figured out why this type of valve has intrigued me so much. It is because this is what I was trying to do a while back. I just couldn't get it down right. But, thanks to Tech, I have since been able to accomplish this.

What I was trying to do is to put a spool type valve in a tee and have it function very similar to a piston valve, while still being more efficient, easier to maintain and operate, and simple to build.


It is ironic that I too have been working on a QDV design using a Tee configuration. Just have to do finalized CAD drawings.

Should be done in a few days so everyone including Tech can critique it!

We can then compare notes.
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Unread postAuthor: Labtecpower » Tue Jan 25, 2011 2:03 pm

I made a drawing in auto-CAD, colored with paint.
Maybe this makes the whole QDV even easier to understand?

Image

Click on the picture to view full size!
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 6:02 pm

Beautifully rendered schrader valve there ;)
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Unread postAuthor: Technician1002 » Wed Jan 26, 2011 1:46 am

Labtecpower wrote:I made a drawing in auto-CAD, colored with paint.
Maybe this makes the whole QDV even easier to understand?

Click on the picture to view full size!


Very nice drawing. may I suggest extending the bumper toward the piston so the piston can't strike the reset ring on the rod? It needs to retract out of the way before the piston starts to move. When it moves, it goes back until it hits something. It should hit the bumper first.
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Unread postAuthor: Labtecpower » Wed Jan 26, 2011 3:32 am

I still have the CAD-file, so a modification is easily made.
I forgot to draw a bumper. The reset ring should retract into the bumper.

@JSR:

I was too lazy to draw the internals, or put threads on it :D
But, according to your reply, its is recognisable as a schrader :wink:

Improved version:

Image

Now with a reset rod not perforating your hand, and a bumper :wink:
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Unread postAuthor: Technician1002 » Wed Jan 26, 2011 5:49 am

Mine retracts all the way through the bumper and beyond it before the valve opens. This prevents impact if the bumper compresses more than expected.

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Unread postAuthor: Labtecpower » Wed Jan 26, 2011 6:16 am

I don't think there will be any problems with the piston hitting the reset ring.
If the piston opens, the ring is retracted into the solid tube, beyond the bumper.

I'm thinking of making one, with a friend of mine. What sort of size do you suggest for a first build?
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Unread postAuthor: Technician1002 » Wed Jan 26, 2011 6:37 am

My first build was a 2 inch. It is the ABS cannon in my sig. The metal ones are harder to build if you don't have metal skill.
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Unread postAuthor: Labtecpower » Wed Jan 26, 2011 11:24 am

I'm on a school specialized in metal working / machine building. I have skillz! :D
I have a dislike of using plastics, because of the lower safety factor and durability.
I think i'm going for an air tank made out of an old propane tank, like yours, I can weld it at school.
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