SpudFiles

Looking at building a simple, but powerful pneumatic cannon. This post is my attempt to gain as much information regarding my build before purchasing or finalising the design.

In regards to specifications, the cannon will be a single shot muzzle loading variety, with a barrel diameter of approximately 2.7", a length of between two and six feet, and a 4 litre CO2 cylinder as the chamber, operating at up to 500 psi.

What my actual concern is, what kind of performance difference will I have between using a 3/4" QEV or running the chamber directly through a 1" solenoid valve.

QEV in question is a KKP-15 1/2" quick exhaust valve.

Solenoid in question is a 5241015 multi purpose pilot operated diaphragm type solenoid valve.

Also, on a related note, does anyone know the diameter and thread pattern on a standard 2.6kg CO2 bottle?

Boltoway wrote:What my actual concern is, what kind of performance difference will I have between using a 3/4" QEV or running the chamber directly through a 1" solenoid valve.

Honestly? I'd say that neither is really up to the task for a ~2.7" bore, particularly if you're looking to get the most out of 500 psi.

A 1" valve is kind of a joke for a barrel that diameter, let alone a 1/2" valve. (You say both 3/4" and 1/2" - I assume you mean 1/2", as that's what the part code you gave looks up as). A 1" valve behind a 2.7" bore would be okay for a functional, but fairly low velocity tennis ball launcher made ut of hardware store parts, but if you want power, you need to go up several sizes.

For a comparison, I've thrown some rough figures into GGDT.

Assuming a tennis ball as ammunition (that being a common choice for that calibre), a 6 foot barrel and a 4 litre chamber, a 2.5cm (~1") valve and 500 psi will yield about 190 m/s & 1055 Joules of energy.
The same launcher with a 5cm valve would be recording 292 m/s & 2480 Joules. (In fact, it beats the 2.5cm valve at less than a third of the pressure - at 150 psi, it clocks in at 195 m/s).

Push that up to a 6cm valve, and you've got 322 m/s & 3018 Joules. And with a full bore valve, you could be bouncing tennis balls off the sound barrier.

The short answer: Neither, but if it has to be one or the other, you really need the solenoid valve. The larger flow area will far outweigh the slight opening time advantages of a QEV.

Ragnarok wrote:Honestly? I'd say that neither is really up to the task for a ~2.7" bore, particularly if you're looking to get the most out of 500 psi.

Thank you for the detailed reply. Firstly, I apologise for listing the wrong solenoid valve. The valve I listed is the 1/2" model, but the same valve does come in 1".

Air restriction due to small diameter valves was definitely a concern of mine. I actually was looking at these particular valves for a different project when I considered involving them in this discussion.

I think one of the problems I will run into is finding a air chamber that has a port large enough to facilitate any valves over 1", without fabricating my own, which I could do, but I'd much rather not do, as I suppose there is a sense of security using a chamber pressure tested to over 3,500psi!

Thanks again, I will continue this endeavour.

Burst disk ?

Consider constructing your own valve, and instead of using an extinguisher, use 2" threaded pipe, which is readily available here if you know where to look. I wouldn't call a piston valve trivial to construct, but certainly simple enough with basic tools and skills.

farcticox1 wrote:Burst disk ?

A suggestion worth considering, while it takes time to set up it definitely offers the best performance for the lowest cost especially when it comes to big bores.