Prim Compact gasoline stove

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

  1. gieorgijewski

    gieorgijewski Subscriber

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    in simmer range subject...
    valve hole is more important
     
  2. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @gieorgijewski
    Good point. That would be harder to narrow down/reduce.
     
  3. gieorgijewski

    gieorgijewski Subscriber

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    from instruction:
    18 strokes - minimal
    25 optimal
    100 maximal
     
  4. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Useful. I’ve been doing ‘optimal’.
     
  5. gieorgijewski

    gieorgijewski Subscriber

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    primkompaktburnerx.jpg
    most elegant idea is:
    - new valve rod with two angle simmer shape
     
  6. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    I agree, or a much shallower taper than on the spindle at present. Some work needed.
     
  7. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @gieorgijewski
    Success!

    80-90 pump strokes on 2/3 full tank, so well-pressurised.

    Mad Max as before.

    16F3CCA2-4B2B-4AFE-A919-6831A71D97B1.jpeg


    A medium setting, probably the ‘go to’ setting for boiling a kettle of water rather than the crazy max billowing flames up the side of the pot and wasting fuel.

    D3518B16-8F49-41BC-8D39-85633076079F.jpeg


    At last (trumpet fanfare) a decent simmer setting. Easy to dial in, reliable output with no pulsing or flip into underburn.

    CEB7FF15-0CD4-496E-B0ED-762C91467CA5.jpeg


    I’d kept an Optimus regulator spindle with mangled rack pinion teeth for jobs such as this. Profile of the Optimus spindle tip clearly a much shallower taper than the Prim one on the right.

    5685EA31-A6E9-461F-9F6A-9E8BCB660DD2.jpeg


    The blackening of the tip of the Prim suggests some blow-back of vapourised fuel-borne carbon from a slightly rich mixture. It also demonstrates the excessive size (around 2mm diameter) of the fuel outlet the valve spindle was asked to regulate.

    067A0AA2-ED04-46BC-B814-215C06EEB4B8.jpeg


    The spindle is short. Telltale is how the spindle’s wrench flats only just emerge in their entirety from the packing nut when the valve’s shut.

    CCCB453C-2DCD-4303-8147-A9A511D2D305.jpeg


    So, no excess of material on the existing spindle on which to form a new tip profile, given that in doing so, a shallower taper would make the spindle disappear more into the valve.

    Below, (bottom in the photo), the tip profile I want, formed on the salvaged Optimus spindle. I used a technique I’ve used often for small components like this of clamping an electric drill horizontally on a bench, clamping the spindle in the chuck jaws and with the drill set to a low-ish speed, getting a Dremel abrasive wheel to work on it to ‘rough out’ the profile. Finishing is done with a fine hand file on the rotating work.

    05CC7569-462B-4E9A-91E3-7ED2205DC95E.jpeg


    Cutting a length off the tip of the new profile I drilled a hole in it’s mating surface with the Prim spindle onto which I ‘turned’ (electric drill technique again) a projection to fit the hole - providing a positive joint to prevent movement when silbrazing the two together.

    41926668-9BC1-42AB-A441-151482D2C202.jpeg


    Silbrazed and cleaned up. I popped it back in the drill chuck and shortened it a fraction to arrive at the optimum length. Polished when rotating too. I installed it in the valve and rotated it a few times with the control wrench to help it bed in. Visible is a burnished ring defined by the mating surface in the valve block.

    FDFE4350-0CEA-470A-920B-DB3AFF094D2B.jpeg


    New graphite packing, fuelled up and fired up with the results you’ve seen.

    Valve spindle flats now more evident thanks to optimised spindle length.

    97235C02-EC08-489A-96E1-3C92135EB015.jpeg


    Thanks again to Gieorgi for his contributions to this project and, behind the scenes but we had a chat about it off-forum, to Reese (@cottage hill bill) who also concluded that a shallower taper to the spindle would achieve the elusive simmer.

    My conclusions about the Prim Compact? Some work on it has turned it around in my estimation and it’s got the potential to become a good performer.

    I already admired some aspects of the design and build, but the lack of a controllable output let it down badly.

    Such an easy thing to have got right at the point of manufacture by making the spindle a little bit longer and with a shallower taper.

    1 out of 10 I would have rated it. An 8 now!

    John
     
    Last edited: Feb 17, 2020
  8. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Only fair I mark it up accordingly.

    457B0DAE-8D2D-4E65-91EB-94AA561541C3.jpeg

    EC534524-7441-45EF-9673-E70F5339B4CE.jpeg
     
  9. Twoberth

    Twoberth United Kingdom Subscriber

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    Brilliant fettle John. Bet you are well pleased (well I can tell you are).
    8/10 for the stove, 10/10 for the fettle.
     
  10. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @Twoberth
    Thanks Duncan, high praise from one who’s scratch-built a regulating burner!
     
  11. gieorgijewski

    gieorgijewski Subscriber

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    it is good, very good, - You reached Your taget...
     
  12. ArchMc

    ArchMc SotM Winner Subscriber

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    Another tour de force. I'm amazed by what you seem to effortlessly knock out.

    ....Arch
     
  13. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @ArchMc
    Thanks Arch.

    I’m but a tinkerer with respect for the range of skills and abilities other CCS members have, whether fettling or other.

    I was watching a TV programme the other night on Renaissance woodcarver Grinling Gibbons, whose work I’ve seen ‘in the flesh’ in some stately home or other. It’s truly awesome work, yet when his ornate carvings fell out of fashion he took up the only work available to him of marble sculpture on grave monuments. Thing is, his lifetime subject focus had been still life and fantasy figures such as cherubs.

    He’d never had to produce a likeness of someone and his funerary monuments were constantly criticised and sent back for re-working. From being a wealthy master craftsman with Charles II as a patron his fortune dwindled to nothing and he died virtually penniless.

    The moral I take from that is that there’s always something to learn. Oh, and that it was probably as well that I followed a line of employment that didn’t leave me at the mercy of fickle, demanding customers!

    John
     
  14. Twoberth

    Twoberth United Kingdom Subscriber

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    I consider myself to be a ‘jack(ass) of most trades’ but a master of none.

    I like to learn new skills and become reasonably competent, but unlike Mr Gibbons above, I have never found any that I am particularly keen on or noticeably good at.

    The one skill I have never mastered is ironing. Never lose your ignorance, you can never get it back!
     
  15. Twoberth

    Twoberth United Kingdom Subscriber

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    That last sentence should read ‘the one skill I am still totally useless at....’.
    I have never mastered any of them.
     
  16. Simes

    Simes Subscriber

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    An unending supply of charcloth then @Twoberth. :)
     
  17. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Final instalment!

    I wasn’t happy with the spirit cup. A bit too small.

    CA3DAE53-3C85-43FC-BB6C-B739AA18CBEB.jpeg

    30E65FD6-5114-44D9-92CF-01D14A49D6E5.jpeg


    I replaced it with a ‘brassie’ (Primus) spare, larger in diameter - and I think it looks better, in keeping with the brass of the burner bell.

    D93676B6-A116-4039-88F6-6DB71D858DAF.jpeg

    88D75C69-D688-4F4E-9F73-B50DCB444822.jpeg


    It’s a sliding fit on the burner bell riser tube

    19CB4133-1781-41CD-930A-9D08C9CDB6DC.jpeg

    4372E746-9D91-4D74-B7C0-5598A7884362.jpeg


    There’s no need to create a seal to the riser because unlike the original aluminium spirit cup, the profile of the Primus cup surrounding the riser reaches higher than the level of a full cup of priming fluid.

    0C569338-ECC1-4CA1-979C-59A10AE988C5.jpeg


    The cup needs to move up on the stem for stowage in the case.

    8377DC21-3643-4401-AE69-5C6EE4B247E6.jpeg

    2A855FAD-1E93-40A9-8FFF-1ED954E797B0.jpeg


    Earlier in this thread I explained that the work I did on the control spindle increased its length. That created a slight problem in stowing the stove tank assembly. Essential now to have the fuel pipe angled right into the corner of the case.

    A92037F5-5566-4035-A083-9DA604CDCCA3.jpeg


    To achieve that the stowage clip had to be bent to the left. The scratches on the paintwork show that clearance is minimal. Strange to think that the stubby control spindle and impact of that on fuelling (no simmer) may have been dictated by the box dimensions!

    5F38AAAF-838D-4D13-A62D-ECE43B61696B.jpeg


    To conclude, I’d to cut some of the stowage clip away to clear the larger-diameter spirit cup when the stove’s in use.

    271AE707-5668-4FDF-8E34-AE233895DF50.jpeg

    @gieorgijewski
     
    Last edited: Feb 18, 2020
  18. Twoberth

    Twoberth United Kingdom Subscriber

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    If you have enough spare spindle sticking out when the valve is in the closed position you could increase the length of the flats by a few mms and then cut the same amount off the end. This should give a looser fit in the box and you would still have the same amount of purchase on the control wheel shaft.
     
  19. Aleks-S

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    Additional washer(s) (1,5..3mm).
    (May vary in the certain Prim-compact)
    Same time may increases underburn risk.
    Should be balanced by test and try.
    Mixture_correction_equipment.jpg
    It is about puff-puff (flame pulsation) because of horizontal fuel tube w/o wick.
    Just my thought:

    1) "Power stroke"
    Evaporation creates more pressure and consumes calories in evaporation zone.
    It creates "puff" in the flame and gurgling in the tank.
    Vapor intrudes into the tank, condensing there, and...

    2) "Inlet stroke"
    ... new portion of liquid fuel streams in to the fuel tube.
    Same time, new calories run towards them from the bell to the "meet point" (evaporation zone).

    And new cycle starts.

    Long time working on full power (or simmering) decreases "puffing-gurgling" effect, because
    the evaporation zone become wider with more fund of calories and shifted closer to the tank
    (or, correspondingly, shifted closer to the bell, and probably with less fund of calories, which is not enough to complete "Power stroke").

    One user from russian site measures temperature during working where preheating cup - it was ~150C.
    Flame-Puffing_and_Tank-gurgling.jpg

    I was not measure it, but by feeling - slightly less power, but far less noise!-) With additional (sectional-folded) wind/heat shield - almost the same as bare with roarer bell. Originally, Ogonyok tends to overheating, and with more massive Shmel's bell - not.
    When below zero tempereature enveroment - silent may work worse, with poor power (wind/heat shield obligatorily required).
     
  20. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @Aleks-S
    I’m very grateful to you for your excellent reply and your work with stoves.

    ... and thanks for helping me with my total lack of Russian language!

    Best wishes.

    John