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CQEV Cannon

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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CQEV Cannon

Unread postAuthor: Slauma » Mon May 30, 2011 5:29 pm

Here's a cannon I've been tinkering with for a while. It uses not one, but two QEVs, so I've dubbed it the CQEV (Cascading QEV) cannon. It's probably not the most efficient use of two QEVs but I've been accumulating parts for a while now and had them lying around. Here the specs

Main Valve: 3/4" Deltrol QEV
Secondary valve(s): 1/4" Deltrol QEV & 3-way push button valve
Barrel: 1/2" Copper (pictured), interchangeable with 1/2" or 3/4" PVC barrel (not sure of the lengths exactly)
Ammo: marbles, AA batteries, empty co2 cartridges... anything that fits
Extras: secondary exhaust noise dampener (also functions as a stock), breech-loading, paintball gun grip, barrel support, safety-valve

The "secondary exhaust noise dampener" is just the extra piping attached to the exhaust of the smaller qev. The longest 3/4" pipe section is filled with some steel wool and a home made baffle (some rubber disks with spacers on a threaded rod) and it reduces the extra noise from the secondary exhaust a noticeable amount.

Typical operating pressure is around 100 psi. I have a 115psi pop-off relief valve on it right now so I can't take it any higher than that. I plan to replace it with an adjustable pop-off in the future. You can't see the 3-way DCV very well in the pictures because of the grip but I know some of you are familiar with this type of valve. It's rated for 115 psi but I know other have used it at higher pressures. Anybody have any idea what kinds of pressure these DCVs can handle (or what the potential risks are operating them at higher pressures)?

The DCV allows bolt-action-ish potential with a constant air source (all I have is a bike pump right now), or even semi-auto if I make a reloading mechanism. I'd like to try for semi-auto, I have a double-acting air cylinder I think I can manage something with, but there're lots of kinks to work out still.

I'd like to make a wooden frame/stock for it to make it look a little neater while keeping compactness in mind. Maybe something similar to a production rifle, any ideas?

Lemme know what you think.
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Unread postAuthor: POLAND_SPUD » Mon May 30, 2011 5:56 pm

not bad
I see it has a dcv, that gives a +25% bonus to coolness factor

Anybody have any idea what kinds of pressure these DCVs can handle (or what the potential risks are operating them at higher pressures)?
most of them are quite sturdy - it's just an aluminium/brass block with a cut hole through it, and a spool

just check how well it works at 20-30 bar - some of them work just fine
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Unread postAuthor: al-xg » Mon May 30, 2011 7:37 pm

Yeah, depending on the design some may leak over the rated pressure, but as POLAND_SPUD mentioned I would be quite had to actually destroy most of them without substantially higher pressures.


A very simple set up for semi auto firing is to connect the air cylinder to the chamber and just use it as simple acting with a return spring to operate the breach.

You may be able to use a more compact elbow to link the QEV to the barrel or use a T and use a solid bolt to lad projectiles from behind. That would reduce the high of the setup making it more similar to production rifles.
I would personally probably just fall down the same old path and make it a bullpup (longer barrels make sense on airguns), I'd probably get rid of the pilot QEV, find or make a direct reduction from 3/4" to 1/8" or what ever the DCV is in and just run the a push fit line all the way to the DCV in the grip. The grip would probably go under the barrel just ahead of the chamber.
I'd carve some wood for a foregrip, buttstock and protective cheek rest.
But then It would end up looking nothing like a traditional production rifle.

Or, forget the above, swing the chamber round so its pointing out the back, move the grip up and slightly forward (leaving room to accommodate for a vertical magazine coming down from the breach. Still probably get rid of the pilot QEV and reduce pilot volume. Carve a foregrip and a solid stock to over the chamber.
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Unread postAuthor: Slauma » Mon May 30, 2011 11:00 pm

I've seen that air cylinder setup work before. The only air cylinder I have right now is double acting (no spring return). I was thinking one possibility might be to connect a small air reservoir to one side to work like an air spring. Or I could just make it spring return by attaching a spring to the bolt.

I'd like to get the barrel closer to the chamber, but I haven't found a way to make it more compact than what I have now (threaded bushing with a chopped down elbow epoxied in). The threads seem to take up a lot of space no matter what. I wish I could just chop the threads in half but that doesn't work with tapered threads.
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Unread postAuthor: al-xg » Tue May 31, 2011 5:59 am

I have used some elbow that didn't have the hexagonal part. I did notice there was a lot of unused thread throughout the build. Can you not get hold of some parallel pipe fittings ?

If not could you not enlarge the ID of the fitting enough to poke the elbow all the way down (or use an elbow a size under) and cut off the top part of the fitting. As long as the elbow is securely glued in it should be fine use.


Yeah an external spring is what I had in mind, although an air spring would be pretty cool if you did get it to work.
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Unread postAuthor: POLAND_SPUD » Tue May 31, 2011 6:34 am

an air spring would be pretty cool if you did get it to work.
I'd say that an air spring is even better than a single acting air cylinder.
it's adjustable and double acting cylinders are usually shorter than single acting ones
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Unread postAuthor: daniel0663 » Wed Jun 01, 2011 12:39 am

Man.. It looks awesome, Bet you it's quite heavy. :o
Clean build and looks good.
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Unread postAuthor: Slauma » Wed Jun 01, 2011 9:08 pm

Took some advice and ditched the second QEV, now I suppose I'll have to think of a new name :|

Performance seems comparable (don't really know, haven't done any quantitative tests) although the speed at wich the trigger (DCV) is operated now has a relatively drastic effect on the power of the shot, whereas before it didn't matter how slow you pulled it you'd always get a pretty consistent shot. Not really an issue as long as you remember to make a quick pull.

I originally tried connecting the DCV to the QEV with some hose (first braided then push-to-connect) but wasn't able to get enough flow through either for the DCV to pilot the QEV, so I went with some 1/8" brass fittings which worked out pretty well.

Significantly more compact and lost a lot of weight without the incessantly heavy stock.:thumbup:

I also ditched the grip and intend to make wooden frame/grip/stock. Hopefully I can make it look pretty (anybody know any good guides on shaping your own wooden stock? I think I've seen one on here somewhere)

I'm also working on modifying a copper tee for the barrel/breech that will be more compact than the elbow I have now and also be a step in the bullpup semi-auto direction.

**Added pictures
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