Prim Compact gasoline stove

Discussion in 'Russia' started by presscall, Feb 15, 2020.

  1. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Biggest contributor to underburn on this stove is the gap at the joint between outer cap and inner cap rim created by the ‘ramp’ locking arrangement.

    E2342809-D6E1-4572-808D-67856FB6565F.jpeg


    Flame at the three such gaps around the cap rim flashes back into the burner bell, igniting an ‘underburn’ when the burner is regulated down.

    The kinetic energy of the vapourised fuel stream at higher output settings prevents blowback and underburn but creates telltale spikes of flame down at the joint near where the gap is greatest at three points.

    92BAEB1D-7CE7-453F-A047-E56DCC23D76B.jpeg

    9EDACEE8-1174-43AC-A49C-D85066F474B0.jpeg

    7FA4A816-D2A8-4B55-8820-31C2664725E0.jpeg


    Solution was to apply a fillet of silbraze at those points on the outer gap, blending them in by rubbing the cap joint on a flat abrasive surface.

    Tendency to underburn at very low settings has been cured.

    53CA8D29-C094-4EBB-98CB-5E16F43A5B0A.jpeg

    “Final instalment!” I said, but this stove has thrown up some intetesting topics, helped by @gieorgijewski and @Aleks-S
     
  2. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Sorry Duncan, I inadvertently overlooked your sensible suggestion.

    I still might do as you suggest. Although I gained adequate clearance by tweaking the stowage clamp to cant the stove fuel pipe a bit more inline with a box corner a little more clearance would be the icing on the cake. Thanks.
     
  3. Twoberth

    Twoberth United Kingdom Subscriber

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  4. Aleks-S

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    A Prim-compact shpindle has 1мм thread pitch (20% less than PT-1 and Ogonyok, which has 1,2mm).
    This partially compensate less sharp taper than of PT-1 and Ogonyok).
    And with Your add-on it gives far more accuracy for power regulating, which unavailable for other stoves.
    Great job!

    And thank You very much for kind words. This is a honor for me.
    I learn a lot on this site.

    The language lesson - is lesson for me. "Motion picture" is not in vain so called. I had to add animation, or pictures at least.
     
  5. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    The O-ring pump worked ok, but as I described in THIS post in the Fettling Forum it had a certain harshness.

    I’ve replaced it with one made up from salvaged ‘brassie’ components, incorporating a leather pump cup washer.

    From this ...

    6F30F0AF-0C18-4946-9090-E015CC7F4623.jpeg

    2269A05A-101F-4F4F-8DDB-860DEB0AC743.jpeg

    ... to this.

    3D5534DA-5E5F-4463-A74D-334E838823DD.jpeg

    0362A77B-E020-40ED-8444-B4E49AD1E431.jpeg
     
    Last edited: Feb 22, 2020
  6. gieorgijewski

    gieorgijewski Subscriber

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    What i have read
    PK - was produced in 3 pumps designs:
    - Shmell/s - what WE saw at primary photo's,
    - classic colemans with valve
    - classic leather pump cup washer
     
  7. Aleks-S

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    Prim-compact has 2 type of inner cup of a flame spreader.
    Later of them has a trumpet on the lover end of central tube. Early - not.
    I suppose it also affects on simmering capability.
    Prim_compact_inner_cup_with_trumpet.jpg
    There are also variations of piston material - brass (early) and aluminium alloy (later).
    Prim-compact_early_pump_piston.jpg
     
  8. gieorgijewski

    gieorgijewski Subscriber

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    Alex
    about simmer /regulation range or easy precision/ truth is:
    it is big hole valve

    weak simmer is when - cold (wet - energetic) gas - is heated in burner bottom
    - proper simmer is when - gas from gas generator - is hot and pour but high pressure

    i think - secret of that construction is in - "last minute" design changes
    and someone forget "leave place for" and insert "structure" in gas generator

    -------------
    1 way
    generator must be hotter
    fuel need to be restricted
    2 way
    add something to the generator space - for improving vaporisation surface
    -----
    or 1 and 2 together

    ----------
    it is "setting up" point of works - when "big hole valve" -proper simmer - burner power - pressures - are condition

    We can change:
    - entry pressure(tank)
    connected with
    - fuel flow / by restricting
    - raising generator temp. by heat back "repairing"

    imo - can be importand - in low power mode...
     
  9. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @gieorgijewski @Aleks-S
    It really just needs:
    • the valve spindle tip to be re-profiled
    • the gaps under the rim of the outer cap filled
    • a larger spirit cup
    With those modifications the Prim has one of the most controllable regulated burners I know - seriously - and the least prone to underburn.

    Restricting the fuel flow when the Prim is equipped with a pump that’s not the most efficient is counter-productive.

    John
     
  10. gieorgijewski

    gieorgijewski Subscriber

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    Yes - good...
    ------
    My example is controllable regulated too.
    maybe not "the best" - but is ready for work
     
  11. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    I took the Prim Compact along on a hike, and shot a video clip to demonstrate the burner’s controllability. The noise wasn’t the silent burner - in the background was a reservoir overflow, in action after all the rain recently.
     
  12. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Night fell.