Making a Silent Burner Cap

Discussion in 'Fettlers Master Class' started by BernieDawg, Oct 16, 2008.

  1. urbanmedic

    Offline
    Joined:
    Apr 5, 2011
    Messages:
    87
    Older thread, but I have been curious about making a similar silent burner cap. I read the note about copper being only semi-suitable due to its degredation due to the heat. I see that pipe caps are available in brass, bronze, and stainless steel. Would a suitably size brass or steel pipe cap work?
     
  2. Wintercamper

    Offline
    Joined:
    May 9, 2012
    Messages:
    4
    Your cap is beautifully made, and inspiration indeed. I have a Primus No.71, it has the same burner as the SVEA123 and the Optimus8, self priming and runs on white gas. No one seems to make a cap for this, so your design has inspired me to have a go.
    I have tried various grills under the roarer flame spreader cap, some give a nice silent burn but all have some degree of underburn. Also the grill tends to impede the gas flow slightly and make the flame slightly rich, which results in orange flame tips, which can blacken a pan a little.
    Has anyone out there tried this approach rather than the full cap? - Ian
     
  3. kerophile

    kerophile United Kingdom SotM Winner Subscriber

    Offline
    Joined:
    Sep 23, 2004
    Messages:
    11,459
    Location:
    Far North of Scotland
    Hi, here is a link to Gary's mini silent damper operating on an Optimus 80, which is very similar to your Primus 71:


    https://classiccampstoves.com/threads/11908



    If you mean by grills, a wire gauze, I can't see how this, placed under a flame plate, would act as a silencer.
    Whatever changes you make to the burner, you must remember that you still need to have flames impinging on the burner bell, in order to get some heat conducted to the jet and tank for vaporisation and tank pressurisation.

    Best Regards,
    Kerophile.
     
    Last edited by a moderator: Jul 2, 2015
  4. Wintercamper

    Offline
    Joined:
    May 9, 2012
    Messages:
    4
    Hi, thanks for your reply. My stove looks just like the one you reference, but my tank is stamped as a Primus No 71. The tin box housing looks identical though. The burner bell has a 35mm diameter ring shape that could support a cap at the right place.

    I understand that, as you point out, any burner must have the flame impinge on the burner bell to heat the gas generator section.
    The gas jet hits the underside of the flame plate and then spreads radially out to the plate edge. About 5mm from the centre the gas velocity has reduced be the same as the flame propagation velocity at that point, and so a ring of fire exists outside this radius. The roar is due to the turbulence of the gas flow and flame advance of the circular flame face.
    So why not put something at that point to anchor the flame?
    This is in fact what the outer cap is doing, providing an anchor point for the flame. The problem with the cap design is that the gas/air mixture inside is combustable and liable to underburn if any flame gets to it.
    On my kitchen gas stove, the gas burner uses a similar principle to the cap. But the flame cannot light back to start in underburn because a) there is no possible flashback path, b) the burner holes will not support flashback through them (similar to the gauze in a miner's Davey lamp). This is because the holes are 7mm long in a white metal casting. The holes are 4.5 x 1.5mm cross section area. They must have done their sums because flashback does not occur through these holes however low the gas setting is.
    So how about a ring of radial holes a few mm long starting at about 5mm from the centre of flame plate?

    I have had some success but the ring of holes does present a slight resistance to the gas flow, enough to slow the gas inside the ring enough to support a slight underburn here. It does quieten the flame, but even a slight underburn is a problem to be avoided. Haven't tried a gauze, I think you would need a longer length of hole than the thickness of gauze, but I will try it and see.

    Regards, - Ian
     
  5. BernieDawg Banned

    Offline
    Joined:
    Feb 23, 2008
    Messages:
    1,656
    Hi Ian
    In your post you say -
    "The problem with the cap design is that the gas/air mixture inside is combustable and liable to underburn if any flame gets to it. "

    There is no problem with the cap design. The design does not allow any flame to get inside the cap. The cap follows the basic principles that were developed over a hundred years ago by Primus, Optimus, Radius and others. Millions of silent burning stoves were produced over this time period and used quite successfully by their owners. Properly designed, maintained and operated silent burning stoves should not experience underburn. Almost invariably, underburn is caused by user error, dirty stove parts, or incorrect parts affixed to an incompatible burner.

    If you closely examine the data I posted in the beginning of the thread you will find that the diameter of the holes that are in the caps are much smaller than you are trying to use. Your openings are simply too big. Beyond a diameter of 1.5 mm (maximum) diameter, you are almost guaranteed to get underburn flashback. One millimeter diameter holes are more ideal.

    Underburn is also related to number of holes. If you have the correct diameter of holes but have too many holes, the vapor pressure at each hole will be too low at simmer pressures/flow rates and the flames will fall into the interior of the cap causing underburn.

    Properly designed caps must consider the total outflow area represented by the total of the diameter of the outflow holes. Caps must also be designed to accommodate the flow volume and pressures of the particular stove.

    Trying to compare your kitchen range (with it's much, much greater gas pressures and volumes) to a tiny Primus 71, a self-pressurized stove, is ill-considered.

    Please examine again the data that I collected on commercially produced caps and base your experiments within the ranges I have indicated. If you simply follow those guidelines, you will almost certainly find success as this data has proved successful for the big stove companies for many years. It has also proved successful with my own products and most recently with some of my imitators - even the ones with zero fabrication or tool skills.

    You also say, "I have a Primus No.71, it has the same burner as the SVEA123 and the Optimus8, self priming and runs on white gas. No one seems to make a cap for this, so your design has inspired me to have a go."

    This is not true and you should consider doing more research before making these sorts of statements. Primus made caps for small stoves like yours in the early part of the last century. Searching the threads here at CCS for references to the Primus #4200 cap should help find some more information on this rare beast. This is the cap on which I based my minicap designs and which Kerophile has so graciously linked you up to above. You can find more about this cap at this link, including full dimensions and specs:
    BD Cap Specs

    Good luck.

    Cheers,
    Gary
     
    Last edited by a moderator: Jul 2, 2015
  6. Wintercamper

    Offline
    Joined:
    May 9, 2012
    Messages:
    4
    Gary,
    Many thanks for your really informative reply! Lots of new info to think about .... !
    Thanks, - Ian

    Why are stoves so interesting . . ?
     
  7. Nordicthug

    Nordicthug R.I.P.

    Offline
    Joined:
    Oct 31, 2004
    Messages:
    3,967
    Why in the Wide, Wide World of Sports would any sane person desire a silent 123, 71, or any other small self pressurizing stove? Half the wonder of these little beauties is the pulsing fighter jet roar while they busily heat your food, or boil the water you need for coffee or tea. It does not compute and makes my poor lil' brain itch.

    I need a drink. Preferably an expensive imported flavored ethanol. Bruichladdich, this time, I think. Yes, Bruichladdich. Neat, of course. I can sometimes be harsh, but I am not a savage.

    Seriously confused ol'

    Gerry
     
  8. RonPH

    Offline
    Joined:
    May 1, 2009
    Messages:
    5,870
    Because its possible to silent a roar-er :lol: and allow it to whisper :thumbup:

    Ron
     
  9. BernieDawg Banned

    Offline
    Joined:
    Feb 23, 2008
    Messages:
    1,656
    Seriously Nordicthug?

    Why try to reengineer silent caps for small roarer stoves?
    1. because it's fun?
    2. because Primus built them originally for their roarer stoves? (which you would know if you did a little research about stoves here at CCS)
    3. because it's polite to silence one's stove while making morning coffee so as not to wake others up?

    Alternatively, I suppose, one can swagger about, demonstrating no skills or abilities, no knowledge, no interest in expanding themselves or abilities, and wake everyone up in camp just so's they can get the attention they crave after a night of drunken self-indulgence.

    Bit like your post, actually, which added nothing to the thread. Like so many posts here at CCS.

    "Little men with little minds and little imaginations go through life in little ruts, smugly resisting all changes which would jar their little worlds."
    - Zig Ziglar, author and motivational speaker
     
  10. Matukat

    Matukat Subscriber

    Offline
    Joined:
    Jan 7, 2008
    Messages:
    4,690
    Location:
    Pueblo West, Colorado, U. S.
    Awwwwwwww...geesh. :( :(
     
  11. bajabum

    bajabum R.I.P.

    Offline
    Joined:
    Dec 23, 2005
    Messages:
    7,368
    Here we go again...
    Lighten up, Gary!
     
  12. BernieDawg Banned

    Offline
    Joined:
    Feb 23, 2008
    Messages:
    1,656
    Nope. Sorry. Ain't gonna happen Steve. [-( Guy criticized my work, said I was insane for doing it, was *very* negative about it. Why should I be nice to that? Pfft. This is a stove site fer chrissakes. If ya got some knowledge or talent and something of real value to say about stoves, then please chime in to the threads I initiate.

    If you are here for social networking, la-de-dah pointless fluffy discussions about bs, or just sad and lonely friend-finding, try Facebook. Or better - stay in The Lounge. Thats what it is there for. Please don't gunk up useful or informative threads on actual stove topics with mindless and off-topic blather.
    Thanks.
     
  13. Colin robert United Kingdom

    Offline
    Joined:
    Sep 4, 2018
    Messages:
    12
    Location:
    Cardiff
    Where do you get them?
     
  14. snwcmpr

    snwcmpr Subscriber

    Offline
    Joined:
    Nov 16, 2011
    Messages:
    13,038
    Location:
    North Carolina
    Search eBay, and Google, for BernieDawg caps.
     
  15. kerophile

    kerophile United Kingdom SotM Winner Subscriber

    Offline
    Joined:
    Sep 23, 2004
    Messages:
    11,459
    Location:
    Far North of Scotland
  16. z1ulike

    z1ulike United States SotM Winner Subscriber

    Offline
    Joined:
    Mar 6, 2010
    Messages:
    2,587
    Location:
    Santa Barbara, CA
    Shapeways sells the full line of BernieDawg caps. They are well worth the money.

    Ben