SpudFiles

That really sounds good. My only concern is that before the piston's o-ring is slammed back, some fuel will find its way inside and may possibly ignite despite being sealed off with the o-ring. I mean, even if it does, the cannon will just either not shoot or will shoot poorly.

I doubt this will be a problem. The pilot will be purged with air and the leak won't be "fuel" is will be fuel air mix which will then become too lean. The mass of the ring in relation to the piston is low and there is little blow by involved in moving the ring when the gland is relatively small. When charging my QDV cannons, the amount of blow by to set the rings is very low. Make the groove just barely wider than the ring and just deep enough to contain it without bottoming when compressed into the cylinder.

velocity3x wrote:

Moonbogg wrote: Ideas, comments all welcome please.

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The chamber being 16" long will leave a lot of unsupported material extending beyond the lathe chuck jaws. Also, how do you plan to bore the inside of the chamber? The bore is 16" deep. Have you devised a plan to make such an extremely deep bore? Even boring from both ends will require deep boring.

Heavy wall tubing, not bar stock.

EDIT: Taking light cuts with an extension should work fine.

Fnord wrote:Ever considered adapting a toolie-style design to this? With the piston impacting in the rear (hey!)you'll be able to add more structural support and bumper than the somwhat thin housing in the current design, and it will also be easier to service the whole chamber.

You also may be able to cut down on the weight a little with a toolie design

EDIT again:

A toolie may result in the need for massive pilot pressure due to the huge surface area of the rear toolie piston face. I will think it over though as I may be missing something.

@tech: The more you explain the check valve 0-ring idea the more I like it. Also, what would you think about me incorporating a piston design like the ones you use? Do you think it would have a benefit over the design I have now? Basically, my design already is a combination of your valve and a barrel sealing valve. I thought about using your design strictly, but ran into issues with balancing the pressure and/or finding a way to stop the piston short of the barrel, so it evolved into your design with a barrel sealing function. So, thanks for the inspiration!

A toolie may result in the need for massive pilot pressure due to the huge surface area of the rear toolie piston face. I will think it over though as I may be missing something.

The back part of a toolie does not need to be the same diameter as your chamber ID... use a sleeve or similar.

Ok, so let me get this straight. No matter which piston design I use, I will have to have a rod going toward the back which opens a port and vents the pilot upon firing? I mean thats fine I guess, but it makes things more complicated. If I don't do this, then I can expect massive piston bounce right? Cause that can't be good.

EDIT: Also, without this pilot venting, there will be residual pressure and no way to vent the chamber of spent gasses....oh balls!

I can't tell you for sure about the piston bounce; no one has ever recorded clear evidence of its effects in a hybrid. Using a bumper with a high level of internal hysteresis will help. Neoprene or any rubber that doesn't bounce very well will be your best bet (hysteresis is basically internal friction that is produced when the material is elastically deformed).

And yes, you're likely to have residual pressure without a pilot valve. I experience this personally with my second piston hybrid, but it wasn't really a big deal since I could just fill/fire it as a pneumatic to vent.

I suggested a toolie because I believed it could solve more engineering problems than it caused. This is a tricky build to begin with but given how nice your other cannons are I think you should be able to handle it. Right now it's just about weighing your options and figuring which design would be best based on your budget and capabilities.

I am wondering about piston weight and friction affecting performance. So, for your simple opinions, do you think a heavy piston, such as a toolie piston or aluminum barrel sealer piston would adversely effect opening speed and performance? Or is the pressure so high upon opening that it just doesn't matter anyway. I mean, once it cracks open a little, my concern is that before the full volume of gasses will have a chance to act on the projectile it will have left the barrel already at less than the cannon's full potential to propel it. If I am being over paranoid you can let me know at any time

I hope I don't get grilled for double posting, but I wanted to show the general idea of a toolie piston that Fnord recommended. Have a look and let me know what you guys think about the concept. I am concerned about piston weight affecting performance, but otherwise I think it looks pretty good.
There will be a o-ring seal at the rear of the pilot, and the rod moves back allowing the pilot to vent. Bumpers would be added and a plate bolted to the rear to contain the back end of the toolie so it doesn't slide out of the sleeve upon filling the pilot.

I'm not getting how it would seal, it looks more like a balanced QDV Are both ends of the piston the same diameter?

jackssmirkingrevenge wrote:I'm not getting how it would seal, it looks more like a balanced QDV Are both ends of the piston the same diameter?

The sealing end of the toolie has an o-ring on it and the toolie rests in front of the vent holes. The back of the toolie also has o-rings and the back of the toolie is a larger diameter than the front. So, upon ignition, the two faces of the toolie play tug of war with each other until the back end wins and the toolie slides backward, out of the way of the vent holes. Bumpers would be in back so the front will only slide in the front end tube. The long rod doesn't experience any compressive force, only tension.

I don't know if this was mentioned, but why not have something like this, you have control over your pilot pressure and low piston weight, coupled with the volume and flow advantages of a spool type piston.

jackssmirkingrevenge wrote:I don't know if this was mentioned, but why not have something like this, you have control over your pilot pressure and low piston weight, coupled with the volume and flow advantages of a spool type piston.

Tech suggested something like that, but would the pilot vent upon firing? Or would it stay pressurized and act like a constant air spring?

EDIT: Nice drawing edit by the way.

Moonbogg wrote:Tech suggested something like that, but would the pilot vent upon firing? Or would it stay pressurized and act like a constant air spring?

Easily compensated for by adding a pop-off valve, if you can live with having to repressurise the pilot for each shot

Nice drawing edit by the way.

Joys of MS Paint, though certainly not as professional as your original schematic

Just a though, could you put the piston more towards the rear of the chamber to reduce weight by shortening the piston rod and reduce overall length? This would make less chamber volume but maybe you could make it longer to compensate?

he might as well go for my qdv breech loaded hybrid design

that would reduce chamber volume even further but all in all I guess it's already relatively large

Fail post. Lol, mod delete please, sorry.