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Coleman Fuel/Air Tubes and Instant Lighting Explained

Discussion in 'Fettlers Master Class' started by toonsgt, Apr 22, 2012.

  1. toonsgt

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    The question of how the Coleman fuel/air tube works comes up quite often. This is an example of how the instant lighting feature works. Regardless of the application, be it a stove, heater, lantern or other instant lighting device, the process is the same. Here I attempt to explain the instant lighting system that uses the fuel air rod. The newer, plastic F/A tubes are briefly mentioned, but lack the manual instant lighting that is the focus of this explanation.

    A quantum leap in the convenience of using gasoline(naptha/CF) lanterns and stoves came with the introduction of the "Instant Lighting" or "Instant Gas" system. Prior to it's introduction, preheating the generator was necessary in order to vaporize the fuel prior to lighting the stove or mantles.

    The idea was to introduce and atomized or spray mixture of fuel and air that was able to be combusted cleanly, allowing the appliance to be lit without a manual preheat.

    The instant gas valve was basically the same design on all gasoline appliances for over 50 years and is still used one some stoves.

    The key components are as follow(forgive nomenclature errors)

    1. The fuel pickup tube: The smaller solid tube that feeds from the bottom of the fount to the fuel valve or fuel distribution block.

    2. The fuel/air(F/A) needle or rod: The innermost part of the assembly which travels up and down inside the fuel pickup tube, and can be spring loaded and riding against, or connected directly to, the actuating mechanism. This partially plugs or completely opens the fuel pickup orifice

    3. The fuel pickup orifice: Connected to the bottom of the outer tube. This is the point at which the fuel initially enters the path.

    4. The air tube(the outermost tube): This tube has a hole(s) near the top, above the max fuel level. It introduces air from the airspace at the top of the fount and conveys it to the space between the pickup orifice and the bottom of the fuel pickup tube, which is where the magic atomized fuel/air mixture is conceived.

    5. The actuating mechanism: This can be a lever, as on a suitcase or 500 stove, or the main valve stem as on a lantern or HGP. All three operate in different ways, but their mission is the same: Move the air rod/needle down to plug the pickup orifice.

    For this instance, we are given a fully operational model 500 stove that is properly filled with Coleman Fuel and pressurized(25-35 pumps) with the valve in the closed position, and an ignition source such as matches. We will now light the stove and explain the sequence of events as they occur.

    Set the lighting lever to the light position. The eccentric block(which the F/A rod is connected to) that is linked to the lighting lever moves down. Thus the F/A rod moves down plugging the pickup orifice almost completely. However, it is imperative that it not completely seal this orifice and that fuel is able to pass between the rod and orifice.

    At this time the level of liquid fuel is the same in the fount and the space between the outer tube and the pickup tube.

    We now light our match and open the valve 2 full turns. Things start to happen simultaneously here.

    1. The cleaning/regulating needle is retracted from the gas tip on the end of the generator.

    2. The valve unseats allowing flow to begin.

    3. Fuel and air in the fount seek the path of least resistance. The flow rate through the gas tip and the fuel pickup tube are equal(and quite high) at this time. Since fuel cannot get through the now plugged pickup orifice fast enough to satisfy this high flow rate, the lower resistance offered by the comparatively larger holes at the top of the outer tube causes air to be forced from the air space above the fuel level down between the outer tube and the fuel pickup tube.

    4. This fast moving air rushes by the partially plugged and seeping pickup orifice, and atomizes the fuel like a rudimentary carburetor or perfume atomizer.

    5. This flammable fuel/air mixture is forced up the pickup tube, through the distribution block, fuel tube, main valve assembly, generator, and gas tip.

    6. This mixture is sprayed from the gas tip into the mixing chamber where it picks up more air(oxygen) and continues on to the burner where our lighted match ignites the mixture. You can hear a sputtering sound caused by larger droplets of liquid fuel being forced through the gas tip.

    7. This mixture continues to burn and heat the generator until the droplets of atomized liquid begin to vaporize(boil) in the generator and expand at a ratio in the neighborhood of 270:1(? can't for the life of me remember the source of this number but it was a reliable one) Once the generator is at operating temperature, the sputtering sound will go away.

    8. At this point the mission of the instant gas valve is complete as the stove is now capable of self sustaining vaporization due to the hot generator.

    9. The flow rate at the gas tip is the same as it was initially but now, the flow rate at the pickup tube is MUCH lower due to the rapidly expanding fuel in the generator. Newer, plastic, metered orifice F/A tubes rely solely on this differential flow rate for operation and have no F/A rod. The size of the pickup orifice is engineered to perform these functions by itself. And is the reason that lighting appliances with this newer device is more difficult at lower fuel levels.

    10. The burner is now burning clean and probably pulsing slightly because the mixture is now extremely lean.

    11. The lighting lever is now moved to the burn position, raising the F/A rod out of the pickup orifice. The path of least resistance is now the pickup orifice alone due the large differential between the flow rates at the gas tip and pickup tube. (gasses are more fluid than liquids, so though the fuel is vaporizing at 270:1, vaporized gas can travel at a much higher rate through an orifice than liquid fuel can. Any fluid dynamics engineers who care to do the math on this one are welcomed and encouraged to get us a working number on this.)

    12. Additional pressure can be added now or anytime after lighting to replenish the rapidly depleted air consumed during the instant lighting process.


    Notes:
    The outer tube is not sealed to anything. Some are crimped on and loose fitting. This is normal

    With a full fount, you may not notice ANY difference between the light and burn position after the generator is hot due to the combination of head pressure from of the high fuel level and back pressure from the expanding gas in the generator drastically reducing the flow through the pickup tube now being able to be satisfied by the liquid flowing through the partially plugged pickup orifice alone.

    If you over fill the appliance(by not filling it on a level surface or tilting it to aid in pouring) the fuel level can be above the air inlets on the outer tube and the appliance will flood regardless of the valve or lighting lever position.

    In hot weather F/A tube problems can be masked by the fuels natural vapor pressure. Which leads to problems like: "It lit just fine in August but it flooded like crazy in December."

    Feel free to comment or suggest additions or corrections.

    To the mods: I have recently posted this elsewhere, but felt it could be of use to the users here.

    Photos are in the works.

    Mike
     
  2. yonadav

    yonadav Israel Subscriber

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  3. itchy United States

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    Nice write up Mike.

    Especially appreciate the explanation for how some of the modern Coleman appliances get around user intervention. Still, I miss the need for this to be done manually.
     
  4. toonsgt

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    Yonadav, yup. Some good info in that thread. The impetus for this was to have a fairly detailed explanation in a single post. It will need pics and additional info will come. I'll remember something or hopefully others here will chime in with valuable nuggets.

    Thanks, Itchy. I'm no fan of the new ones, myself but sadly, I don't see Coleman producing liquid fueled anything within a couple of years. Hope I'm wrong, though.

    Mike
     
  5. geeves

    geeves New Zealand Subscriber

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    Would I be correct in saying the newer colemans ie 422 533 etc have just down away with the run position so run permanently in the light position? ie always mixing air into the generator
     
  6. yonadav

    yonadav Israel Subscriber

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    I did not check these models, Geeves, but I doubt it.

    Running the stove in the "light" position draws 'precious' compressed air from the tank, forcing you to do more pumping very frequently. I doubt that a stove designer will want his stove to work this way.

    Yonadav
     
  7. geeves

    geeves New Zealand Subscriber

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    Both my 533 and 422 lose power if not pumped up every 10 or 15 minutes. Cooking for one or 2 this isnt an issue but for the whole tribe when you want full noise for 20 minutes or more its noticeable. An Msr recomended 5 or 6 pumps every 10 minutes the coleman needs 20 or so
     
  8. toonsgt

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    533s have the metered orifice F/A tube. If it's running properly, you shouldn't have to pump that much. If cleaning the F/A tube doesn't work, you can make the bottom hole a little bigger(very slightly) to remedy this. Go too big and it will flare on lighting. They don't just run in the lighting position all the time. The back pressure from the hot generator slows the flow rate through the F/A tube thus allowing the the fuel level in the outer tube to rise, sealing air off. When they get low on fuel they tend to start sucking air though.

    Mike
     
  9. geeves

    geeves New Zealand Subscriber

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    I might of overstated the pumping but did have to pump it 2 or 3 times while bringing a 8 pint billy to the boil followed immediately by a second 8 pinter. (pumped 3 times for 16 pints boiling water)
     
  10. bajabum

    bajabum United States R.I.P. Subscriber

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    Hope you didn't hurt your thumb... :lol:
    Sheesh!
     
  11. geeves

    geeves New Zealand Subscriber

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    Each of those 3 times was 20 strokes. No I didn't hurt my thumb. Still that's best part of 30 minutes on full power, not that there is anything else on a 533.
     
  12. bajabum

    bajabum United States R.I.P. Subscriber

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    I never tried to boil thst much at a time, could be normal, I guess.
     
  13. dwarfnebula

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    I had read about how the Coleman instant lighting worked, then I pulled an F/A tube and I got confused. Couldn't figure out how that piece made it work like it did. This picture made sense of it for me, thought it might add to this old thread.
    1347852793-FuelandAirTubeAssembly.jpg
     
    Last edited by a moderator: Jun 26, 2015
  14. rogerzilla

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    Very interesting, thanks.

    One curiosity on new Coleman stoves is that the length of the pickup tube varies. My 533 will suck itself dry but the 442 has a fair bit left in the tank when it runs out at the burner; probably about 50ml (I got it out using a syringe and some thin poly tubing). The 550Bs are similar to the 442.
     
  15. JonD

    JonD United Kingdom Subscriber

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    That is an amazing description of a very clever device.

    It was always possible to hear the atomisation process happening in my 533 and I always wondered how it worked.

    The lack of a rod - relying on a balance of pressure between fuel and air seems critical in the 533. There is an O ring in the pickup tube which fails and messes up the ratios - then it gives all sorts of messing about.

    I really think many owners could be living with the results - much less than the real capability of the stove :lol:
     
  16. JonD

    JonD United Kingdom Subscriber

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    Last edited by a moderator: Jul 1, 2015
  17. Jelte Klas Netherlands

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    //I realize that I'm resurrecting a very old thread, but this seemed better than making a new one.//

    If the fuel pickup line from, for example, an MSR pump would be (first extended, then) bent at a 90 deg. angle, and a tiny hole is made at the elbow, with a hot safety pin, would this work in the same manner as described above?

    After first lighting, the bottle could be turned upside-down, resulting in the large opening in the fuel, and the tiny hole in the air, thus greatly reducing pressure loss. (I hope)
    When the stove should go out, turn it around again, and it will /almost/ blow itself clean.

    Are there any arguments on why this wouldn't work?
    Does anyone know an easy way to get similar tubing?

    Regards,
    Jelte1234.
     

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