Quick Dump Valve

[Hotwired]

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.

[jeepkahn]

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

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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...

[Technician1002]

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-cel ... 17968.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/inde ... ling_valve

[Hubb]

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.

[spudtyrrant]

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

[Hubb]

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.....

[dewey-1]

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.

[Labtecpower]

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!

[jackssmirkingrevenge]

Beautifully rendered schrader valve there

[Technician1002]

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.

[Labtecpower]

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
But, according to your reply, its is recognisable as a schrader

Improved version:



Now with a reset rod not perforating your hand, and a bumper

[Technician1002]

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.

[Labtecpower]

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?

[Technician1002]

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.

[Labtecpower]

I'm on a school specialized in metal working / machine building. I have skillz!
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.