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winterizing spud guns

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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winterizing spud guns

Unread postAuthor: Bowman » Thu May 10, 2012 6:20 pm

I heard somewhere that spud guns tend to malfunction or not work so I almost immediately tried to figure out a way to "winterize" a basic potato cannon. So the concept works like this (will have animation up later). You spray hair spray in the back of the combustion chamber, then you close it up, load your potato, ignite your fuel, and while the potato is traveling down the barrel it will comes across a port on the barrel that lets some of the gas from the explosion to goes into a "sleeve" if you will that is wrapped around the combustion chamber thus heating it up, once the potato exits the barrel it releases the gases from the sleeve, combustion chamber and barrel. allowing it to be re-fired.

So what do ya think?
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Unread postAuthor: jimmy101 » Thu May 10, 2012 7:12 pm

Heating the chamber like that won't accomplish anything except wasting energy.

Even in a closed PVC chamber the temperature rise of the PVC, closed chamber so all the energy ends up as heat in the PVC, is only a couple degrees C.

Wait, I've actually calculated it for a typical sized combustion chamber:
http://www.inpharmix.com/jps/Chamber_Temperature.html
Scroll down to the section "Temperature Rise Of The PVC Chamber"
13F degree rise for a closed chamber. Figure in an operating gun the temperature rise is only a degree F or two.
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Unread postAuthor: Bowman » Thu May 10, 2012 7:18 pm

Well, the reason they don't work in the winter because I guess the cold makes the gas not be able to ignite. So maybe warming up the outside of the chamber would help? That was my basic idea when I thought this up, but I guess I was wrong. Eh, who knows 'till you try, right?
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Unread postAuthor: sagthegreat » Thu May 10, 2012 8:33 pm

The belief for me was that. Stuff like hairparay is atomized liquid. Ad the cold condenses it to the bottom of the chamber so it doesn't ignite
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Unread postAuthor: Bowman » Thu May 10, 2012 8:39 pm

sagthegreat wrote:The belief for me was that. Stuff like hairparay is atomized liquid. Ad the cold condenses it to the bottom of the chamber so it doesn't ignite

Yea it's something like that. I still think heating the outside of the chamber would work. I think that "Jimmy101" is completely over thinking this idea. It's a very simple concept if you just break it down.
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Unread postAuthor: PCGUY » Thu May 10, 2012 9:30 pm

The true problem with using any spud cannon in cold enough temperatures to consider winterizing is that PVC is pressure rated somewhere around 72*F, and the rating does not apply at cold temperatures because PVC becomes more brittle at those temperatures. It's dangerous and typically not advised to fire cannons in winter time temperatures (freezing). Granted a simple combustion generates around 1/2 of what a standard pneumatic can go up to, it still isn't the best idea especially if the cannon is kept outside and chills completely.

Your fuel issues are indeed related to the cold, however if you were using a different fuel you would not have this issue.

Using the cannons own combustion to heat it's self doesn't help anywhere with that, the combustion and pressure spike happens way before any real heating can occur. Not to mention you are indeed losing performance and sending pressure through a series of adapters and parts. Remember, KISS.

Your best, safest idea for shooting in the cold?
-Stand inside where it is warm with the cannon (at room temperature)
-Fuel your cannon (safely of course don't go firing indoors)
-Step outside and fire
-Put cannon back inside
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Unread postAuthor: Bowman » Thu May 10, 2012 9:32 pm

PCGUY wrote:The true problem with using any spud cannon in cold enough temperatures to consider winterizing is that PVC is pressure rated somewhere around 72*F, and the rating does not apply at cold temperatures because PVC becomes more brittle at those temperatures. It's dangerous and typically not advised to fire cannons in winter time temperatures (freezing). Granted a simple combustion generates around 1/2 of what a standard pneumatic can go up to, it still isn't the best idea especially if the cannon is kept outside and chills completely.

Your fuel issues are indeed related to the cold, however if you were using a different fuel you would not have this issue.

Using the cannons own combustion to heat it's self doesn't help anywhere with that, the combustion and pressure spike happens way before any real heating can occur. Not to mention you are indeed losing performance and sending pressure through a series of adapters and parts. Remember, KISS.

Your best, safest idea for shooting in the cold?
-Stand inside where it is warm with the cannon (at room temperature)
-Fuel your cannon (safely of course don't go firing indoors)
-Step outside and fire
-Put cannon back inside


Sounds like a good idea. I just wanted to see if this would work. Thanks.
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Unread postAuthor: Zeus » Fri May 11, 2012 4:30 am

Look, regardless of how it heats the chamber, having a sleeve will reduce the performance significantly. While I'm nowhere near as educated as Jimmy, everything he said makes sense. If you want to preheat your spud gun, take PCGUY's advice.

If it won't ignite, then use propane or butane, it's stupendously easy to set up volumetric metering.
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/sarcasm, /hyperbole
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Unread postAuthor: Goats spudz » Fri May 11, 2012 9:50 am

Wrap it in insulation?
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Unread postAuthor: thrasmussen » Fri May 11, 2012 10:49 am

Goats spudz wrote:Wrap it in insulation?

Or a 12vdc electric blanket.
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Last edited by thrasmussen on Sat May 12, 2012 2:27 pm, edited 1 time in total.
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Unread postAuthor: Moonbogg » Sat May 12, 2012 12:51 pm

thrasmussen wrote:
Goats spudz wrote:Wrap it in insulation?

Or a 12dc electric blanket.


LOL thats a good idea. If you can find some old metal pipe of some sort, then your problem is solved. I mean, nothing fancy at all. Hell, paint cans and duct tape work really well actually and cold weather won't bother it at all.
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Unread postAuthor: Bowman » Sat May 12, 2012 1:58 pm

Thanks guys. Zeus I don't get why you're so mad I did take PCGuys advice. You don't have to basically repeat the exact same thing. I GET IT...
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Unread postAuthor: zeigs spud » Fri May 25, 2012 2:28 am

Cold Cannons can be a problem.mostly dangerous, BUT in the winter the air is Colder, hence more dense, so it is possible to get more power out of it, though more power plus a brittler cannon is a horrible idea... but proof is in the pudding, cars get better gas millage in the winter and lower altitudes.
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Unread postAuthor: Zeus » Fri May 25, 2012 2:50 am

Mad, me? I ain't mad...

Good to see you back Zeigs spud.
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Unread postAuthor: Labtecpower » Fri May 25, 2012 9:56 am

Cold air may be denser, but this will also lower the SOS, causing your guns to have a lower performance.
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