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Super Simple Mini Piston Hybrid?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 2:46 pm

Lockednloaded wrote:That is a much better setup, but I doubt I have that much skillz when it comes to complicated epoxy casting


Why not just make a coaxial? You can make a simple (now that you have epoxy ;)) adapter to fuel through the schrader, no need for a ball valve.
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Unread postAuthor: nature-boy » Tue Dec 14, 2010 4:14 pm

just a quick thought: While using that design, couldn't you also get rid of one schrader and use a piston that is not completely airtight?

Imagine the front schrader gone, you would fill the whole chamber from the back, what would close the piston. Having the ignition in the front/main chamber, the rapid pressure-increase there will force the piston open.
Got it?
Or am I completely wrong with this theory?
Or has this even been build allready?
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Unread postAuthor: Lockednloaded » Tue Dec 14, 2010 4:23 pm

I need the bv for venting, but the schrader adaptor is a cool idea. The coaxial is a much simpler solution, but I don't know if I can sacrifice interchangeable barrels and breech loading for a simpler sleeker design
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 4:23 pm

nature-boy wrote:Or am I completely wrong with this theory?
Or has this even been build allready?


The only thing wrong with it is if the space behind the chamber also ignites , you're screwed.

As to whether in practice this would happen I'm not sure if it's been done in practice. It would certainly make things simpler to have just one valve and a non-airtight piston, heck it would make a very sound cartridge design...
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 4:25 pm

Lockednloaded wrote:I need the bv for venting


Not really. You're pumping the air in, who cares what's in the chamber ;) a few pumps with the piston in the open position will quickly remove any residual gasses from previous firings.

edit: whoops, double post, I meant to edit my previous one :oops:
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Unread postAuthor: Lockednloaded » Tue Dec 14, 2010 4:26 pm

Why not fill from the back through an air tight piston with a check valve, but you'd have to get valve opening pressure correct if you know what I'm getting at
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Unread postAuthor: Zeus » Tue Dec 14, 2010 4:37 pm

Compressing the back means you can adjust the popoff pressure for the peak combustion pressure, if you fuel it for a 10X mix and using that pressure behind the popoff means it opens at ~150 PSI.

The peak combustion pressure is beyond 1000PSI in such a mix therefore greater performance can be reached.

Another problem could be met if one used a oxy propane mix, the popoff would be nearly worthless.
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Unread postAuthor: nature-boy » Tue Dec 14, 2010 4:55 pm

I don't think that the rear-chamber will ignite with a well made/tight fit piston...or did anyone experienced something compareable?
I think the gap will be to small, and the piston will start moving and vent the chamber before the rear will have time to ignite, but that's just my theory..
Why not fill from the back through an air tight piston with a check valve

would work IMO, but if the rear will not ignite, I dont think its necessary.

Compressing the back means you can adjust the popoff pressure for the peak combustion pressure, if you fuel it for a 10X mix and using that pressure behind the popoff means it opens at ~150 PSI

But there will be no need for that, by having the same pressure in the rear and in the front, you would always have the right pressure to "pop"?! Wouldn't you?

Another problem could be met if one used a oxy propane mix, the popoff would be nearly worthless

sorry, I don't understand that... :(
would you bother to explain? :)
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Unread postAuthor: Zeus » Tue Dec 14, 2010 5:05 pm

If the valve opens close to the same pressure as the hybrid is filled, you will have poor performance because the pressure won't build up as high, if the popoff is the same pressure as the chamber it opens at 150PSI.

If the valve opens close to the peak combustion pressure you have around 1000PSI when the valve opens, a massive performance increase.

I'm sorry if my way of writing is confusing, that's how my mind works.
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Unread postAuthor: nature-boy » Tue Dec 14, 2010 5:18 pm

Ok. That makes sense to me!
But you can achieve the same effect by altering the OD of the barrel!
With a larger barrel diameter you will have a smaller area the pressure in the front can act on, and with that increase the opening pressure.
:)
corret me if Im wrong.
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Unread postAuthor: Zeus » Tue Dec 14, 2010 5:21 pm

That's spot on, however it would be quite hard to do, and it needs to be fairly precise.
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Unread postAuthor: Lockednloaded » Tue Dec 14, 2010 10:05 pm

school's really hectic ATM, but I get out friday so I'll be trying my original design first, I know the others are simpler, but I like the idea of using my own even if its really more of an old concept with new materials

And hey, worse comes to worst, I've got a nice little HP full auto valve :D
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 11:53 pm

Lockednloaded wrote:I'll be trying my original design first, I know the others are simpler, but I like the idea of using my own


Fair enough, I prefer to find the simplest route but there's nothing wrong with intricacy if you can make it work :) plus of course as you mentioned there's the option of breech loading and changing barrels available to you.
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Unread postAuthor: Lockednloaded » Wed Dec 15, 2010 9:13 pm

I'm using quite a few more standard fittings than I planned, but there's still a good amount of epoxy in there, but it's added a lot more serviceability and customization
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 16, 2010 1:41 am

Servicability is good :) I'm going to try making a coaxial, I'm liking this idea.
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