Primus 5 Flaring up...

Discussion in 'Fettling Forum' started by Duran, Mar 15, 2017.

  1. Duran

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    Hi Everyone,

    Hope you are all doing well.

    I have a Primus 5 which is not working properly.
    The short of it is, it flares up.

    I have replaced the seals with the ones i got from the Fettle box .

    Assuming it is primed correctly and the burner and jet itself are clean, would an enlarged jet be the only other cause of it? It starts out fine, but after it has warmed up, it starts flaring up at the jet. I am thinking an enlarged jet,but wanted your opinion as well. I dont think the burner itself is clogged up as it hasn't had much use from the looks of it.

    I would appreciate your input.

    thanks,

    Aaron
     
  2. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi, Sorry that you are having problems with your Primus No.5.

    The thing to remember with any kerosene burner, and particularly a silent model, is that the priming stage only heats the burner sufficiently to get it started.
    The full operating temperature is not achieved until the burner has been running for a few minutes, when you can then increase tank pressure to achieve higher power.

    If you start with too high a tank pressure you can flood the vaporiser with liquid kerosene, get liquid coming through the jet, and quench the previously hot metal of the vaporiser. The result is a flare up of liquid kerosene with copious yellow (fuel-rich) flames. All you can then do is shut off the fuel, re-prime, and start all over again.

    There are two additional possibilities,

    1. If the jet aperture is too large the vaporising capacity of the burner can be overwhelmed at full flow. The correct jet for this burner, running kerosene fuel, is around 0.32 to 0.35mm.
    Check the jet aperture with the correct pricker. If the jet aperture is greater than O.32mm diameter it could certainly produce the symptoms you describe.

    2. If the burner has seen long service it could be choked with carbon coke produced by "cracking" of kerosene fuel within the vaporiser tubes. The coke build-up impairs heat transfer to the fuel and it is possible to get liquid fuel exiting the jet and causing flare-ups.
    If carbon build-up is the problem you can rod-out some of the deposits by pushing a flexible wire up the two vaporiser tubes accessible via the base of the removed burner. An airline helps shift any carbon the rodding has displaced. If all the internals of the burner tubes are severely carbon coated you may need to burn the deposits out.

    Trust this helps.

    Best Regards,
    Kerophile.
     
    Last edited: Mar 15, 2017
  3. shagratork

    shagratork United Kingdom Moderator, R.I.P. Subscriber

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    Burners, both silent and roarer are well designed, simple devices.
    Kerophile's comments are 'spot on'.
    If your nipple/jet is new and the correct size, then the problem might be the hidden insides of the burner.
    Purging the burner is described in various places on CCS.

    I posted a very crude method here but the methods advised by Primus (and other manufacturers) are better.
     
  4. tofta

    tofta Subscriber

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    @Duran
    So do you mean below the caps, under the burner head, directly at/over the jet?

    All the best, e
     
  5. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi, if your stove is suffering from underburn:

     
  6. Duran

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    It flares directly over the jet. I am waiting for a replacement jet to see if an enlarged jet is the problem.
     
  7. tofta

    tofta Subscriber

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    @Duran

    That is underburn, the paraffin vapor igniting where it should not.

    The jet most likely is not the culprit in this. More likely is dirt like glowing soot inside the caps, badly fitting caps allowing the vapor to escape, if the jet is to blame it might be shooting the vapor in a wrong direction (it should be concentrated up center of the spigot), easy to see but if the whole burner is crocked one also can get underburn.

    So you have a few issues to investigate before that new jet arrives, or like @kerophile rather humorous suggest – stamps.

    And is you search for underburn here on CCS you can read for a long time ...

    All the best, e

    PS. I think a CCS search will be most effective if you start from Home (top left menu)