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Old 07-16-2006, 08:40 PM   #11
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talk about usless trivia!!!


i went back and found the uel and lel for propane it's 2.1%- 9.5%

first we'll talk real quick about the fire triangle..

3 things are needed to make things burn: Oxygen, fuel, Ignition

Not all fuel is dangerous all the time, that's where the UEL and LEL come into play

for those not familair with LEL (lower explosive limit) and UEL (upper explosive limit...aka ufl Upper/Lower flamable limit) this is the range at which a fuel will ignite

the range for propane is 2.1%- 9.5%

In theory, if there is more than 10% propane mixed with air, it will not ignite. In an enviroment with say 30% propane (you would need a respirator to breath) you could light a match, and the propane would not ignite.

Same goes for concentrations below 2%
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Old 07-16-2006, 09:44 PM   #12
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Curious, are you going to somehow control the propane as well?

It would seem, with a constant flow of propane, every spark after the first one is superfluous, no? I guess that you've figgerd all this stuff out, how to extinguish the flame between sparks and such, but, if the propane discharge is being controlled, whatever controls the propane would control the spark as well.
Don't think I'd worry too much about the unburnt propane floating down around the operator, the bicycle (hopefully) will be moving and the flume will just trail along like smoke from a train stack. Even being heavier than air it still isn't like a rock, takes a while to settle.

I think the auto flasher is the ticket, as you say and don't know but as with all car stuff, would imagine they'd be pretty big power hogs.

Bitchin' project, can't wait to see the photos
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Old 07-16-2006, 11:21 PM   #13
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gonna have an electric solenoid valve to allow the propane to flow.

i should draw a diagram,...perhaps i'll update this post later

the propane is a liquid in the cylinder and only changes to a gas at a certian rate.....in the casae of a 20# BBQ cylinder, the flame is about 4 or 5 feet high as it comes out of a 3/4" pipe, depending on a few factors.

propane always leaves the cylinder as a gas (i'm pretty sure the new opd valves do not allow propane to leave as a liquid, even if you turn the tank up side down)

for the flame thrower application, the gas leaves the cylinder and is allowed to collect in an "expansion chamber" (really this is an old propane cylinder with a non-opd valve...they can be had for nearly free)

The valve is left open on the lpg cylinder connected without a regulator to the expansion tank. This allows propane GAS to build up pressure inside the expansion tank. When a suitable amount of pressure is presumed to have built up, a 3/4" solenoid valve is opened and allows propane gas to shoot out of the 3/4" pipe past the ignition sorce, and a large fireball escapes.

A 1/4 turn valve on the LPG tank allows for quick shut down in case of emergency. Having the pipe that comes out of the expansion tank be over 8 feet tall also adds a good measure of safety (can't burn people if they are below the flame)


Keeping the lpg cylinder at least 20 feet from the expansion tank is another measure of safety. Safety has to be an important priority when dealing with something with as much kinetic energy as a 50 foot flame thrower.

all in all, it's quite safe. There are hundreds of them at burningman, and as far as i know, nobody's ever been killed by a flame during the event.
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Old 07-17-2006, 01:22 AM   #14
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Have you considered a regulator that allows more than the 11 inches of water column a standard one does? Wait....is there even a regulator in this system? It might be a good idea as it will help with the expansion of the gas.
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Old 07-17-2006, 02:06 AM   #15
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Wow, this is going to be quite a device to see on a bicycle ..
So you're looking for a device to control both the spark and the solenoid? Since you say when "a suitable amout of pressure is presumed to ..", I'm guessing that a human makes this presumption and opens the valve and you wish to automate this?
If the varying wheel speed is not a problem, Radio Shack has an IR photo emitter and detector (individual components) - one on each side of the wheel and cards or something else in the spokes to block the beam ... runs on 1.5V and the switch part handles 20V and about 25 mA or so, enough to toggle a relay that would handle the load. Cost is about 3 bucks if I remember right. Wiring is simple, battery to the emitter and two leads out of the detector that switch your load. Don't know how much they cost, but one of those ding-dong things on the 7-11 door would work with something in the spokes to break the beam and replace the gong with the load. Actually those things are just the Radio Shack thing noted above with a gong connected and packaged up.
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Old 07-17-2006, 09:42 AM   #16
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you are a genious! (even if i can't spell it) I love the emiter/detector idea with the spokes from the wheel. That'll take care of the spark on the spark plug...

as far as a regulator goes, it regulates pressure in the system. I want MORE pressure! More pressure = bigger flame.

i don't want to automate the opening of the solenoid. It takes about 5 minutes for pressure to build up in the expansion tank, and this only allows for 1 or 2 blasts of the flame thrower before you have to stop and wait for pressure to build up again. The solenoid is connected to a standard doorbell or other momentary on switch.

Another big problem, that is too difficult to address on the bicycle is the LPG tank icing up. The liquid propane is leaving the cylinder at such a rapid rate that the cylinder literally forms a layer of ice around it. cold propane doesn't build nearly as much pressure as room temperature propane. To combat the ice problem with my bus, i wait till a tank begins to ice up, then disconnect it and set it in the jacuzzi for a while (when nobody's in it) 105* is no where near too hot for propane, and it does a super fast job of heating things back up.
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