Curious discovery on a Primus No.3 burner

Discussion in 'Stove Forum' started by igh371, Jan 29, 2020.

  1. igh371

    igh371 SotM Winner Subscriber

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    Finally getting round to cleaning up, and hopefully recommissioning, one of my Primus No.3s; and one of the first things that happens is that I discover this after unscrewing the burner:
    DSC09711.JPG
    "Some sods been and wrecked a perfectly good burner by plugging it" is my first thought:x; i.e. "my, my, isn't that curious". (Something bad had also clearly happened to the jet as well.) But after a short while examining this travesty; another thought; "that looks to be unnecessary knurling on the protruding end of that reprobate vandal's plug":-s Anyway brief application of a pair of mole-grips quickly had the plug unscrewed:shock: And not only that, the inside of the burner base was also properly threaded!
    DSC09713.JPG DSC09714.JPG DSC09712.JPG DSC09715.JPG

    So what was all that about??? Another quick check revealed that the only other No.3 burner I had loose was threaded inside the base just the same. Why???

    Had Primus gone to all that effort just to make sure a family of spiders didn't set up home in there whilst in storage? Was this a very peculiar way of plugging burners on complete stoves so they didn't become incontinent in transit?

    @kerophile
     
  2. MrAlexxx

    MrAlexxx Subscriber

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    Strange indeed! That is the only help I can offer. This needs a professional to chime in. lol

    Alex
     
  3. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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  4. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    From this thread:
    Prabhat #2 resonance problem
     
    Last edited: Jan 29, 2020
  5. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    From this thread:

    Poor mans T ?41???
     
    Last edited: Jan 29, 2020
  6. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi @igh371 here are photos of orifice plugs and rolled brass gauze plugs used in No.3 stove burners. Thanks to bnk:

     
  7. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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  8. igh371

    igh371 SotM Winner Subscriber

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    Wow, George, you certainly have been busy!!! And absolutely spot on, after carefully studying the photos in brassnipplekey's piece from your last link, then going back my 'blanking plug', and what do you know it isn't a blanking plug it is a restrictor plate with a tiny centre hole now uncovered!!! Brilliant:D
    The other spare burner has neither restrictor nor gauze, so I guess sourcing some new gauze is now on the to do list:lol:
    And I wonder what I'll find in the burner which is still on the other stove?
    Well chuffed that I posted this, many thanks,
    Ian:thumbup:

    @kerophile
     
  9. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @igh371
    I’ve encountered those gauze-screened devices on roarer burners 4131 (for No.3 and No.84 stoves) and 4036 (No.85 stove). They appear (just visible) in the 1961-date Primus burner chart, though not as a spare part curiously, but not in the 1930’s-era chart. Both charts clearly aim to feature detailed illustrations of the burners and not rough representations so I deduce that those screw-in devices were a refinement added to later period burners, perhaps relying on gauze rolls on earlier products, if at all. @kerophile I don’t disagree with your reasoning, George, but when I first discovered the device on removing the burner from one of my No.84 and No.85 stoves I tried both stoves without the device inserted and it made no difference to combustion, with no pulsing or surging. I deduced at the time they acted as a fuel filter to minimise jet blockages. The large jet orifices on each of those burners makes the screening out of the larger particles liable to block them a viable proposition with a gauze weave fine enough to trap those particles but not so fine that fuel flow is restricted, or rapidly clogs.

    John
     
  10. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    05EB7EA2-FB61-4CC7-B6F5-E3506F7913EA.jpeg

    Hi @presscall this is from the 1962 Primus catalogue:

    See part #4749 = inlet nipple.

    Best Regards,
    Kerophile.
     
  11. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @kerophile
    Thanks George. I’ll have to take another look at those burners I have. Gauze or jet orifice?

    John
     
  12. Twoberth

    Twoberth United Kingdom Subscriber

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    Well, I never knew about those restrictor plates as I have never taken the burner off a No.3. But curiosity got the better of me.

    DSC09295.JPG

    My 1960 No. 3 has the knurled jet orifice plate, and a 0.008in (0.21mm) guitar wire fits easily down through the hole.

    DSC09296.JPG DSC09297.JPG DSC09298.JPG

    So easily in fact that I am pretty sure there is no gauze in there as well, but I am reluctant to unscrew the plug as it's stuck in there fast and the stove works well.

    I learn something new on this site every visit. Thanks to all for the information.
     
  13. Tony Press

    Tony Press Australia Subscriber

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    This thread is a great example of why CCS and CPL are such good forums. You get to learn new stuff all the time.

    @Twoberth

    Yours appears to have the hole at the end of a tube, while @igh371 has the hole in the top of the fitting. Is that how you see it?

    Cheers

    Tony
     
  14. igh371

    igh371 SotM Winner Subscriber

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    @Tony Press At the moment I'm seeing 3 different versions of these orfice/restrictor plate plugs: mine, which is the smallest and almost flush with the burner base, brassnipplekey's, which extends further down into the riser tube, and @Twoberth's which goes the opposite way, recessed into the burner base. Does this indicate that Primus were struggling to get a configuration which really did what they wanted? @presscall's observations may be pertinent here. And where did the resort to, or reversion back to gauze plugs fit in?
    Ian:thumbup:

    @kerophile
     
  15. igh371

    igh371 SotM Winner Subscriber

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    @Go Scout's 1959 example shows a similar recessed restrictor as @Twoberth's 1960, but it extends further down into the riser too. So is that a 4th version? Did they ever make 2 batches the same!?
     
  16. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi, extract from Wikipedia:


    Miss Shilling's orifice was a very simple technical device made to counter engine cut-out in early Spitfire and Hurricane fighter aeroplanes during the Battle of Britain. While it was officially called the R.A.E. restrictor, it was referred to under various names, such as Miss Tilly's diaphragm or the Tilly orifice in reference to its inventor, Beatrice "Tilly" Shilling.


    Engine cut-out problems

    The Tilly orificeEdit

    Complaints from pilots led to a concentrated search for a solution. Engine manufacturers Rolls-Royce produced an improved carburettor, but this failed in testing. It was Beatrice 'Tilly' Shilling, an engineer working at the Royal Aircraft Establishment at Farnborough, who came up with a simple device which could be fitted without taking the aircraft out of service. She designed a thimble-shaped brass flow restrictor (later refined to a flat washer) with precisely calculated dimensions to allow just enough fuel flow for maximum engine power. It came in two versions, one for 12 psi manifold pressure and another for the 15 psi achieved by supercharged units.[3]

    While not completely solving the problem, the restrictor, along with modifications to the needle valve, permitted pilots to perform quick negative G manoeuvres without loss of engine power. This improvement removed the RAF's Rolls-Royce Merlin-powered fighters' drawback versus the German Messerschmitt Bf 109E machine, whose Daimler-Benz DB 601inverted V12 powerplant had had fuel injection since 1937. During early 1941, Miss Shilling travelled with a small team to fit the restrictors in one RAF base after another, giving priority to front-line units. By March 1941 the device had been installed throughout RAF Fighter Command. Officially named the 'R.A.E. restrictor', the device was immensely popular with pilots, who affectionately named it 'Miss Shilling's orifice' or simply the 'Tilly orifice'.

    This simple measure was only a stopgap: it did not allow inverted flight for any length of time. The problems were not finally overcome until the introduction of Bendix and later Rolls-Royce
     
  17. Twoberth

    Twoberth United Kingdom Subscriber

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    @igh371
    Having looked at Go Scout's 1959 example, I think it is the same as mine.
    My plug is 10mm deep before the orifice plate.

    DSC09300.JPG DSC09302.JPG DSC09303.JPG DSC09304.JPG DSC09305.JPG

    I can also confirm the hole is about 0.32mm, and there is no gauze inside, as I can spin an 'L' shaped wire (0.012 in diam) inside the hole with no resistance.
     
  18. Staffan Rönn

    Staffan Rönn SotM Winner Subscriber

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    I have a Primus Trading-era (1963 or later) spare NOS burner which I think is the No. 3 burner (part no. 4131). If not - could it be the 4146 burner for the No. 85 heating apparatus? Anyhow - It's fitted with gauze but it has the internal threading as well. Total height of burner is approximately 130 mm. Quite a hefty piece. Images below:

    20200130_133814.jpg 20200130_133831.jpg 20200130_134040.jpg 20200130_134241.jpg
     
  19. Twoberth

    Twoberth United Kingdom Subscriber

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    Louis Carroll was right; 'Curiouser and curiouser! cried Alice'.

    Seems like gauze replaced the plugs. and gauze was fitted to existing burners with internal threads at or around the time of PTC.
     
  20. igh371

    igh371 SotM Winner Subscriber

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    A further issue became apparent once the restrictor issue was resolved, and a spare burner that was without a plug was suitably equipped with a gauze plug. All ready to go, not a chance! Despite all appearances both burners turned out to be seriously blocked, no amount of pressure would produce anything but the poorest of flames with or without gauze or restrictors in place.
    But the jet nipples are larger than those normally encountered. I discovered that special jet removal keys are available, at a price. So the cheapskate option was adopted. A spare standard UJ articulated jet tool was adapted by filing out the jet cut-out to fit (needle files in the very restricted space). Still very fiddly as a standard tool is too small to reach into such a large burner in the normal manner. The assistance of a miniature 3/16AF spanner proved very helpful, a 3/16AF obstruction spanner would have been even better!