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.25 Modular QDV Sub-Rifle (WIP)

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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.25 Modular QDV Sub-Rifle (WIP)

Unread postAuthor: Kensingt0n » Tue Aug 30, 2016 10:30 pm

Hey crew, been lurking the site for a fair while now but haven't posted any threads yet so I figured it was time to change that.

I've been tinkering with pneumatics for a while now and have had a fair amount of success with making some fun little plinkers, unfortunately, my commercially bought 1/4" QEV packed it in recently.
With inspiration sparked by Jack, BtB, Crowley (and every other next level machinist on here :wink: ) I had to persist.

After a short break, the hobby bug kept niggling at me to build my new launcher.
I sat down armed with every fitting and rubber washer I had in the house.
While sitting there I came up with a design similar to what you would find on the french "patator" forums.
I guess it's a direct actuated dump valve? please correct me if i'm wrong. I believe is the same principle as a QDV.
The piston is pushed forwards to sit against the barrel port, air is filled via the Schrader valve and flows into the valve, forcing the rubber face to seal against the barrel port.
When the piston is pulled backwards, the face unseals from the barrel port, allowing the air to exhaust.

The valve housing is a 1/4" female tee, the barrel port is a 1/4" male x male hose tail with the barrel inserted into the hose barb.
The piston is a bolt with a thick rubber washer glued onto the top of it and has a groove cut for the rear o-ring to be seated snug and stay in place.
A 1/4" to 1/8" reducer houses a larger o-ring and slides over the back of the piston and screws into the valve housing to keep it all in place (and airtight lol).

Under all the action is a 1/4" Y fitting which connects the QDV, Schrader and air tank together.
The air tank itself is an old aquarium CO2 canister with some of the thread removed to allow for full flow and a proper fit inside the screw fittings. A 3/8" to 1/4" reducer attaches the tank to the system.

The barrel is a 9/32" OD (7.14mm) brass tube @ ~270mm length using 1/4" steel ball bearings as ammo, nice snug fit.

Any questions/statements please chime in!
Thanks everyone!

1.jpg
Overview - Skeletal


2.jpg
T & Y Config


3.jpg
Valve Housing - Piston end is exposed with makeshift trigger added for smooth & consistent pull.


4.jpg
Piston - Closed position


5.jpg
Piston - Open position


6.jpg
Valve - Piston removed, just a good ol' fashioned tee.
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Re: .25 Modular QDV Sub-Rifle (WIP)

Unread postAuthor: jackssmirkingrevenge » Wed Aug 31, 2016 12:04 pm

Pretty well done with standard fittings, looks like the piston is more or less balanced by sealing the shaft which is quite clever. What pressure are you running at?
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Re: .25 Modular QDV Sub-Rifle (WIP)

Unread postAuthor: Kensingt0n » Thu Sep 01, 2016 6:19 am

Thanks for the kind words JSR, means a lot coming from the infamous "epoxy bandit" :twisted:
Exactly that, quite easy to actuate which I'm pretty impressed with for what it is.
Currently it's running at ~150psi, could easily push it to 250 - 300 I'd say. Unfortunately I'm restricted by the pump I'm using at the moment. The plan is to build a pressure/stirrup pump into the launcher itself. The Schrader fill port will be replaced with the homemade pump and fill the tank directly. Well, that's the plan anyway lol
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Re: .25 Modular QDV Sub-Rifle (WIP)

Unread postAuthor: jackssmirkingrevenge » Thu Sep 01, 2016 9:28 am

The plan is to build a pressure/stirrup pump into the launcher itself. The Schrader fill port will be replaced with the homemade pump and fill the tank directly.


Given what you've already put together this should not be too much of a challenge. If you do so I would suggest a much smaller chamber, maybe even a simple endcap replacing the current CO2 capsule. This will allow you to reach higher pressure quickly and for a given amount of air, a small volume at high pressure will always give you more power than a large volume at low pressure.
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Re: .25 Modular QDV Sub-Rifle (WIP)

Unread postAuthor: Kensingt0n » Fri Sep 02, 2016 6:51 am

Hopefully so, after seeing a few of the tutes on here for pressure pumps, it seems pretty achievable. Especially due to the fact that standard plumping fittings are used for the bottom end of the pumps.
Thanks for the advice, I actually have a repurposed 12g canister as well which will take the place of the current tank once I've gotten my pump together. A 1/8" to 1/4" bushing does the trick nicely :wink:
I had taken into account airflow and how it acts within tubing, but at the current pressure, wouldn't it have a negative effect on the projectiles velocity?

I'll kick myself in the arse and get a video up for everyone soon lol
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Re: .25 Modular QDV Sub-Rifle (WIP)

Unread postAuthor: Kensingt0n » Wed Sep 07, 2016 8:22 pm

Just as a quick update, the pump is being constructed as I speak. I'm about to start getting the check valve sorted, after that it should be smooth sailing.
Using copper for the first time is sparking ideas for FA mechanisms and Girandonni inspired rifles..
Looks like I'll be getting more tubing at some point lol
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