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QDV-Tee-1.5-porting

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: inonickname » Sat Sep 05, 2009 2:53 am

My overall rod length is 12.5 inches long. The large diameter is 1.05 inches

You didn't pick that up why JSR?

Or if you're inclined this way:

My knob is 0.838 inches long.



I believe a better method to adapt a QDV to automatic function is to have a spring behind the piston. Piston goes back, venting the chamber and blocking some kind of air in port. Spring reseats piston, chamber fills again.

Then of course it would need more adaption for full automatic function. Regardless of how good it is (seriously) it doesn't lend itself to automatic function well.
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 05, 2009 3:26 am

POLAND_SPUD wrote:since you're an expert on pop-offs and farting machines :wink: do you think it'll stay open long enough ?


What I was thinking of is basically the well proven QEV+popoff concept but with the QEV's piston attached to the QDV rod, to give the same function but better flow.

You didn't pick that up why JSR?


My personal PC is currently undergoing surgery due to excess heat issues (and I just came back from buying this little beastto help out :D) so I'm currently on a much more primitive setup, such nuances are much more difficult to pick up on...

That's the official version at least :P
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Unread postAuthor: Technician1002 » Sat Sep 05, 2009 11:04 am

It's funny this thread has moved to making this full auto. I don't have any sketches yet, but I have been designing one. Here is how it would be built;

1 The piston has no rod, but does have a small EQ port. The rear of the cannon is sealed and only contains a bumper.

2 The chamber has a pop off that vents into the barrel directly between the piston and projectile.

3 The barrel has a small post to prevent launching the piston.

This is how it would work;

1 Piston is closed and the chamber pressure builds until;

2 The pop off pops open and provides a blast of air between the projectile and piston which;

3 launches the projectile and piston in opposite directions opening the main charge into the barrel. This rise in pressure in the barrel then;

4 vents some into the pilot rising the pilot pressure beyond the pressure of just displacement compression. As the projectile exits and the chamber pressure drops;

5 The pilot area pressure closes the piston sealing the chamber and the remaining pilot area pressure finishes venting back out the EQ hole in the piston.

Process repeats full auto fashion. Think it has a chance of working? :?:
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Unread postAuthor: dewey-1 » Sat Sep 05, 2009 11:20 am

Well guys I will look into an auto/semi-auto QDV CAD model.

Just give me a few days of thinking and preparation.

Meanwhile, I am trying to get Tech's 1 inch QDV Launcher done.
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Unread postAuthor: Brian the brain » Sat Sep 05, 2009 3:12 pm

If you could make a normal barrelport, like in a regular pistonvalve, where the seat diameter is exactly the same as the inside of the piston housing, you don;t get the wear and tear on the front O-ring..



You could also cover the back of a reservoir with neoprene, and use a sliding barrel ( with O-rings)

Your barrel becomes the valve.You could even make it breechloadable that way by having a plug there.

Upon seperating the barrel from the rear of the reservoir, pressure difference will kick in and slam the valve ( barrel ) forward...opening up to full flow instantly.
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: Technician1002 » Sat Sep 05, 2009 3:37 pm

Brian the brain wrote:If you could make a normal barrelport, like in a regular pistonvalve, where the seat diameter is exactly the same as the inside of the piston housing, you don;t get the wear and tear on the front O-ring..


In the full time I have owned all 3 QDV's, I have never had an o ring failure. The bumpers on the other hand do get beat to death as shown in the photos above. This includes the ABS Test cannon (aka the apple cannon), the T shirt cannon and the Marshmallow cannon. The o rings in all 3 still look new.

Replacements are about 70 cents for the large and 30 cents for the small. Wear of rings is not an issue at all.

I have considered breech loading, but gave up designing a way to quickly open and seal the breech. I considered dirt and shavings of stuff may cause problems with the seal and decided against sliding objects through the greased valve segment.

A sliding barrel could be a reliability issue with alignment and torque on the barrel. I went with a solid uni-tank/valve construction. Guests have dropped my cannons. A broken barrel fitting is not the end of the cannon, just a barrel that can be easily replaced.

Upon seperating the barrel from the rear of the reservoir, pressure difference will kick in and slam the valve ( barrel ) forward...opening up to full flow instantly.


This full flow instantly claim must be tempered with the reality that the moving mass that is "moving instantly" is the entire barrel, a part considerably more massive than my piston. I'll race you! :D
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Unread postAuthor: Brian the brain » Sat Sep 05, 2009 3:47 pm

Ah...indeed...that is true...
Maybe the " barrel" part should be replaced by a " Bolt"
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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