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Some quick questions

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: c11man » Tue Jul 13, 2010 11:54 am

with a qev's large piston to seat ratio opening pressure is going to be far from ideal. it will open way before ideal chamber pressure is reached and you wont have nearly as good of preformace as you would with a burst disk or a with a more optimal homemade piston valve.

becuase of this low opening pressure the popoff will NOT be responsible for opening the valve, as tech said the pisotn will comress the pilot area and the popoff will then open. the popoff will keep the valve open longer which is probably a good idea.
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Unread postAuthor: Lockednloaded » Tue Jul 13, 2010 11:55 am

so this project should not happen. I did not plan on making this complicated, I just waned an easily changeable cannon system from hybrid to semi pneumatic to full auto pneumatic. I don't want to blow this up; if that ever happened I would be banned from spudding.

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here's a quick sketch
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Unread postAuthor: c11man » Tue Jul 13, 2010 12:00 pm

if you build it correctly it wont blow up, the problem is getting it to work and with desent preformace
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Unread postAuthor: Lockednloaded » Tue Jul 13, 2010 12:02 pm

so I'll get a 150psi pop-off and start a 2x
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Unread postAuthor: bhoben » Tue Jul 13, 2010 12:28 pm

I am trying to build a pneumatic potato or apple launcher for my corn maze this year. Is the sprinkler valve the best route to take and is a 1" valve big enough? How much holding capacity and at what psi do I need. Also what is a good size barrel for potatoes?
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Unread postAuthor: c11man » Tue Jul 13, 2010 2:26 pm

Lockednloaded wrote:so I'll get a 150psi pop-off and start a 2x


you will want the popoff to be as close to the prignition pressure of the chamber as possibe without it leaking. also 2x will give you preformace easily surpased my a pneumatic with moderate pressure
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Unread postAuthor: Lockednloaded » Tue Jul 13, 2010 5:01 pm

awesome, I ordered 3 QEVs off of Mcmasters today, I can't wait until they get here!

on an unrelated side note, has anyone ever pressure tested one of these aluminum sigg bottles?
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I am trying to build a pneumatic potato or apple launcher for my corn maze this year. Is the sprinkler valve the best route to take and is a 1" valve big enough? How much holding capacity and at what psi do I need. Also what is a good size barrel for potatoes?

wrong topic sir
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Unread postAuthor: D_Hall » Tue Jul 13, 2010 5:58 pm

bhoben wrote:I am trying to build a pneumatic potato or apple launcher for my corn maze this year. Is the sprinkler valve the best route to take and is a 1" valve big enough? How much holding capacity and at what psi do I need. Also what is a good size barrel for potatoes?

Yes, a sprinkler valve will do it, but why? You can get a QEV for not much more money and it's a lot better suited for the application, and safer to boot!

Honestly, I just don't grok the popularity of sprinkler valves.
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Unread postAuthor: Hotwired » Tue Jul 13, 2010 7:51 pm

Once you rule out ultimate power as one of your aims I can see appeal in sprinkler valves.

Inline, available in store instead of mail/online order and are plug and play with an electrical switch.
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Unread postAuthor: Lockednloaded » Tue Jul 13, 2010 7:53 pm

whats with the completely unrelated hijack?!
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Unread postAuthor: Hotwired » Tue Jul 13, 2010 7:59 pm

That would be me browse-by posting to the last post I saw :)
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Unread postAuthor: Lockednloaded » Wed Jul 14, 2010 4:55 pm

ramses wrote:The solution would be using the exhaust of a pop-off connected to the chamber to open a pilot valve on the QEV.


I'm sorry, I don't fully understand. How about a quick sketch for me please?
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Unread postAuthor: Lockednloaded » Mon Aug 23, 2010 10:10 pm

I thought I'd bump this because I am now seriously looking into this project.

As far as piston hybrids go, this may not be the most powerful hybrid out there, but it will surely surpass the capabilities of a moderately high pressure pneumatic.

So I plan to build this with the 3/4" QEV and 90 psi pop-off because i have been told that the closer the pop-off is to preignition pressure the better. the gun will be used a 4X mixes.

Any thoughts, objections, or concerns?
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Unread postAuthor: Fnord » Tue Aug 24, 2010 1:06 pm

I have an idea.

You're worried about the qev opening at a lower than optimal pressure due to surface area ratios, right?

A solution might be to modify it to operate in the chamber-sealing configuration, rather than the stock barrel-sealing mode.
Meaning, you patch up the normal equalisation hole and drill one between the pilot area and barrel port. Then put the chamber on the barrel port.

Look what happens to your surface areas.


D_hall wrote:Honestly, I just don't grok the popularity of sprinkler valves.

I've never heard anyone use 'grok' in a sentence until a few weeks ago when I read A Stranger in a Strange Land... Now I'm hearing it everywhere. :?
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Unread postAuthor: SpudBlaster15 » Tue Aug 24, 2010 1:34 pm

Lockednloaded wrote:Any thoughts, objections, or concerns?


It should work fine. I've never had a QEV apart, so I can't tell you what surface area ratio you'll be dealing with here, but even if the valve opens at below the optimum pressure, the launcher will function quite well.

As we discussed in the chat, when using a pop off valve as a vent, be sure to keep the dead pilot volume as low as possible. This will minimize the quantity of pressurized air trapped in the pilot chamber when the vent valve reseals.
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