SpudFiles

With floating rings I lost them at only ~30 PSI on a 1 inch piston. With stretch to fit rings and no space for air to get under the ring, it may stay on place much better.

I'd rather not risk the o-rings coming off. If I get the design wrong the first time, its going to really suck having to modify and possibly machine new parts. But, thats why I ask for help before the build and not how to fix all kinds of easily prevented problems after the fact. I like the inside barrel QDV piston. I am comfortable with it unless something better happens to come up.
I have chosen to redesign the chamber and end cap configuration. Upon further digging, research and more digging, I discovered that increased thread engagement does not yield any real benefits as the pre load forces are acting on the first 6 threads, with over 30% of the load being on the first thread alone and then it exponentially decreases as you move up the threads. So after 6 threads, the benefit is not there. As a result, I will use tie rods and bolt to the outside of the caps like a standard air cylinder configuration. I will, however, try to make it look as sexy and unique as possible.
A problem with that came up as well (of course). The estimated 3,800lbs of force that each tie rod will produce will cause the aluminum to yield at the nut face. This can hopefully be remedied by using high strength washers to distribute the load.
So this build is challenging, but until every worry is put well to rest, I will not attempt the build. Then again, I won't let up until its finished either. Thanks for the help everyone, it is progressing much much faster and will end up being a much more worthy design than I could produce alone.

Yo,

Would you expect the o-ring to expand into the slots too much and possibly bind between the piston and the piston housing inner wall? Those are 1/2" slots and their combined area is a little more than the area of the port cross section, but I wanted to open them to even 5/8" to allow more flow to try to compensate for any friction or flow resistance as well as allowing more flow faster than having to wait for a complete piston opening.
5/8" slots left even a more narrow array of space to keep the o-ring held down.

I am not using the pressure you are proposing, but using 2 inch wide ports on my QDV has not been a problem with the o rings. They do expand out into the ports, but once the pressure lifting them is gone, they return back into the piston groove. I worried that when I used floating o rings in my prototype t shirt launcher that the possibility existed that an o ring would get caught between the piston and edge of the port. The prototype was built to see if the 2 inch ports would be a problem and would need to be broken up into smaller ports, but it worked without any issues.

My 2 inch pipe has a 7.5 inch circumference. I cut 3 ports 2 inches wide by 1 inch tall for 6 sq inches of port area. This left 3 bars between the ports 1/2 inch wide. This gives a total port area almost double the barrel area. Ports = 6 sq inches. Barrel port 3.14 square inches.

It looks like you are using 6 ports. It should be OK.
Big wide ports worked fine up to 100 PSI.

Just wanted to share the progress on the design.





Fill manifold coming out the back. Steel hex caps with aluminum plug style components to reduce weight while getting strong end caps for the studs to bolt against.

Is that a breech load on the barrel?

The design looks great. I do believe that is a breech loader.

That would be a breach load.

Sweet This looks like it will be sick.

Gun Freak wrote:This looks like it will be sick.

Pass it a bucket then, yeeesh!

It would be cooler if you put the air and fuel into the piped under the chamber, would make it real clean looking like all your other ones.

Crna Legija wrote:It would be cooler if you put the air and fuel into the piped under the chamber, would make it real clean looking like all your other ones.

I agree for sure. Its just that I don't want to drill any holes in this particular cannon's chamber as it reduces pressure rating. I'll see what I can do. Aesthetics is very important to me.

Any progress on this? Hadn't noticed it before but it's something I wish I had done with my 10X, perhaps a little different piston design, but still the same idea.

I agree that aesthetics are a good compliment to a good working design.

Also good call on getting rid of the inside wall butting - that would of been a bitch to do lol. If weight savings were your goal an external stepped wall would have accomplished the same thing with an oversized pipe to alleviate the loss in volume.

In your current design are you using tie rods to keep the caps on? I'm working on the design for my next gun and tie rods vs creative circumventive design was a big "aesthetic" question lol.

mobile chernobyl wrote:Any progress on this? Hadn't noticed it before but it's something I wish I had done with my 10X, perhaps a little different piston design, but still the same idea.

I agree that aesthetics are a good compliment to a good working design.

Also good call on getting rid of the inside wall butting - that would of been a [female doggy] to do lol. If weight savings were your goal an external stepped wall would have accomplished the same thing with an oversized pipe to alleviate the loss in volume.

In your current design are you using tie rods to keep the caps on? I'm working on the design for my next gun and tie rods vs creative circumventive design was a big "aesthetic" question lol.

In the endless battle for weight vs power, I decided that tie rods were just the strongest and simplest way to do it. Threaded end caps might have worked, but the design gets complicated when trying to incorporate a piston housing on the front end. Steel end caps are used here however for strength.
Right now I am sitting back and reading new posts, rethinking some things and just paying attention to anything that might make the design better before I take the plunge. This has already paid off with the following example. Tech mentioned a way to remedy one of my biggest concerns in another thread regarding pilot air compression and heating in a non vented configuration. I am actually going to utilize that now by running a tube from the pilot to the main support structure and have additional pilot volume in that structure tube.
That tube was going to be used for propane metering, but not I can go manometric and use the tube for pilot volume. So, just by being patient and doing nothing, the cannon has already bene improved to at least a 2.0 version
I got itchy and almost bought material, but i'm glad I waited. Sorry for such a long post.