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DYI's Hardhat

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DYI's Hardhat

Unread postAuthor: DYI » Tue Dec 28, 2010 1:10 pm

Every year after winter break, my university runs a hardhat decoration contest as part of the winter festival. I decided to enter said contest, and began design work on my hat back in October. I've worked on it intermittently ever since, and began construction on the 22nd.

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The basic concept is a medium-sized propane burner mounted on top of the hat, with ignition placed about a foot out from the brim. The implementation is somewhat trickier. As I elected to use the readily available 1 pound tanks, there was an issue with the tank cooling down to the gas's melting point, and staying frozen for a very long time. To mitigate this problem, the tank is submerged in an outer vessel filled with warm water, which I've found to cut down the "recharge" time by about 95%, or more depending on ambient temperature. I'd like to emphasize that this is *NOT A FLAMETHROWER*. It does not use a flammable liquid and behaves much like a very large, poorly mixed blowtorch.

The main gas flow originates from a 2 gallon "buffer" tank in series between the liquefied gas tank and the burner. This allows for the projection, for roughly 2 seconds, of a reasonably impressive three metre jet of fire from one's head, even in the temperatures encountered outside my house at this time of year (granted, the water does have to be almost boiling to mitigate the frigid climate at the moment :roll:).

The initial plan was to use solenoid valves for all gas flow controls, but due to an issue with an online ordering system, it looks like I'll be doing manual operation of the main gas flow with a 1/4" ball valve mounted in a handle, with 3/8" airline running up and down my arm. The gas flow was deemed too violent for direct ignition from a spark, so a pilot light is being used, which will be ignited by a standard piezo "clicker". Over all, the system will be made more awkward by the all-manual operation, but it should still be tolerable.

Mounting all of this on a round hardhat without damaging the hat was something of a challenge, but two slots on the sides provided just the foothold I needed. 1/8" x 1.25" steel flats are pushed through the slots, bolted on the bottom side to prevent slipping out, bent on top and drilled. The bends and mounting holes in the top plate are done such that the flats are under a good deal of tension, and the top plate is held down very securely on the top. No amount of shaking I can apply to it causes any wobble at all, anywhere.

Included for your enjoyment is a video of the second test, taken in high definition with a Casio EX-FC150. The buffer tank pressure on this shot was only 100psi, but the burner performed very well. At higher pressures (the highest tested so far is 130psi), the hat develops enough thrust to flip itself over backward, but not enough to cause significant discomfort to the wearer.
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Unread postAuthor: Technician1002 » Tue Dec 28, 2010 1:21 pm

There are a couple of options to fix the heat of vaporization problem and the drop in pressure and temperature.

I wished I knew of this sooner. I would have pointed you to the burners used for hot air balloons. They face the same issue. The solution is to draw liquid from the tank at normal room temperature and heat it in a tube with the flame. This vaporizes it at the normal warm tank pressure without the cooling of the liquid. This provides vapor (gas) to the burner jet.

Do you have a source of stainless steel tubing? Is it too late to modify it?

Here is a double burner for a hot air balloon.
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I got to try my hand and running a hot air balloon as part of a ride I took when I got engaged. I got engaged in a hot air balloon.

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Last edited by Technician1002 on Tue Dec 28, 2010 1:32 pm, edited 1 time in total.
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Unread postAuthor: DYI » Tue Dec 28, 2010 1:29 pm

Thanks for a good suggestion Tech, but in my particular case that isn't really possible, or necessary - a single fill of warm water lasts about 20 fills, or 5 full tanks of propylene. :wink:

On large burners, using the heat of combustion to vaporize the liquid is certainly the most practical solution. Interesting that the burners in that balloon look to be producing a flame quite similar to the one I'm getting out of this.
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Unread postAuthor: Moonbogg » Tue Dec 28, 2010 2:59 pm

Awesome vid! Hey Tech, I got engaged in a hot air balloon also! That makes us like, connected in some special way doesn't it :lol:
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Unread postAuthor: Fnord » Tue Dec 28, 2010 5:38 pm

Are you going to leave that 5 pound slab of steel in one peice? Seems a bit excessive for a mounting plate :)

Also, maybe the bracket that holds it to the helmet itself can be formed on a roller rather than a press brake. The right-angles look kinda funny.
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Unread postAuthor: ramses » Wed Dec 29, 2010 12:34 pm

Moonbogg wrote:Awesome vid! Hey Tech, I got engaged in a hot air balloon also! That makes us like, connected in some special way doesn't it :lol:


There was a story on the news a while ago about some guy who was going to do that, but dropped the ring off the balloon :roll: , but proposed (successfully) anyway. I think he found the ring afterward.

This reminds me of when I filled my hybrid with pure propane and shot it out over a propane torch.
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