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My first serious project

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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My first serious project

Unread postAuthor: Roy_Battey » Fri May 15, 2015 8:27 am

Hey guys,

So this is my first serious project. Basically, I plan on making an all steel/brass spring-loaded ball valve actuated QEV gun this summer. My goal is to be able to reach 200+ ft-lbs with .495 lead roundballs and/or fully penetrate a pine 2X4 at 600 psi, although I worry about needing an obscene barrel length.

I've attached a quick sketch of my plans below, as well as a GDDT file for anyone who's curious. The numbered labels indicate the following:
1 - Stock
2 - Crossbow style trigger
3 - Hook
4 - 1/2" ball valve
5 – 3/4” QEV (I’m thinking one from Alpha Technologies)
6 – Door latch (used as a crude ladder sight)
7 – 1/2” type K or L copper barrel (approx. 50” long)
8 – Strong spring
9 – 3/4” galvanised steel air chamber (approx. 40” long)
10 – Hose clamps (my readily available “barrel bands”
11 – Fill valve, Schrader (will add a smaller BV in front to allow topping up with my 600 psi shock pump after I reach 350 psi with my bicycle pump)
12 – Ramrod housing
13 – Exhaust port
I’m still sourcing all of my parts, although I have most already and know what I need to get to achieve the desired result (except for maybe a decent QEV that I know will handle 600 psi and offer a good flow coefficient).

What I would like is some feedback on my design from some the experts. I would love to know how it can be improved. Also, I was wondering if there were some tips and tricks for working the metal of the ball valve handle with limited tools/resources. At the very least, I would like to add a nice backward curve, to make it more aesthetically pleasing and aid in opening times. I know my stock is ambitious, but I’ve found some good tutorials on that on this site, so I’m fairly confident about that.

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Re: My first serious project

Unread postAuthor: Tep » Sun May 17, 2015 10:57 am

Hi Roy,

Great work getting started on a "proper" launcher!

Your overall design while deffinatly sound is probably significantly more complex than it needs to be. the main area of overdesign is going to be in that trigger / pilot system you have; in its current set up the spring opening of the ball valve to pilot the qev is basically totally overkill and while it will probably net you slight power increases over some other methods these will probably not end up being worth it.

It he design you have there is ideally suited to giving you one powerful shot (between pumpings) and if that's all you want from it I would suggest doing away with the ball valve all together and simply using a very small valve , such as a schrader or presta valve from a bike tyre welded/ braised / epoxied (securely) into an appropriate brass fitting to fit the back port of your qev.

With proper setup you could easily use this as your fill port too.

The trick to piloting a qev with a small valve is to get the volume of air behind the qev piston (between it and the valve / atmosphere) as low as possible. Most of the time I fill any space behind the piston with epoxy leaving a hole for the air to escape through obviously.

If you do this you will be able to make the whole thing go off just as well by simply pumping up the contraption through the bike valve and then when you are ready to shoot open the valve using a lever (a simple stick trigger going up through the stock ( I'll attach a diagram tomorrow) and you will get the same effect if not better.

With proper leverage on the trigger it will be super easy to fire.

Like I said I'll put a diagram up tomorrow when I'm back on the computer.



Adit: get a fridge compressor. You will probably want to kill yourself trying to pump that up with a shock pump.

Edit: Here is a really crap diagram drawn in a shoddy mac version of paint.

basic qev.jpg

I should probably point out that this is not even vaguely to scale... you would need to workout your chamber size etc in GGDT or just wing it or whatever.
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