More Petromax vap surgery

Discussion in 'Fettling Forum' started by presscall, Aug 2, 2020.

  1. presscall

    presscall United Kingdom Subscriber

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    In THIS post I silbrazed over what I thought was a pinhole leak. I was wrong in that there was no pinhole. Had there been, the spike of hot gas would surely have broken the glass and on igniting would have undoubtedly attracted my attention. I fell prey to that old enemy of fettlers, falling short on the diagnosis in order to follow the easiest option to implement, resulting in more time and effort to get back on the right track.

    I was right however that the Petromax Preston loop was scorching the glass on my Hipolito 150cp.

    It was that bit closer than the original Hipolito loop to the glass, being of a slightly larger diameter. Too close.

    2E79C1B8-48D5-45A7-B323-83FAAB77110D.jpeg


    I’d already decided that the Petromax vapouriser wasn’t quite right for my lantern. You can see from the above photo and the one below how much ‘beefier’ it is than the Hipolito one and double-priming became the norm. The loop on the Petromax item also came too low down the lantern cage and part-masked the mantle.

    9638C0B9-A7CE-443D-8B26-779FFF71644B.jpeg


    I initially went down the route of rectifying the worn Hipolito jet by silbrazing in it a hypodermic needle insert. While I pondered on fabricating a jet needle to be compatible with it (the Petromax needle wasn’t) I tried out the jet nipple in the lantern. It still ran too rich. Turns out the hypo needle was too large a bore (gauge) and I should have gone with the alternative I identified in that post.

    So, after these false starts, I decided to cut the nipple threads portion off the Hipolito and Petromax vapourisers and silbraze the Petromax equivalent onto the Hipolito vapouriser. I’d then have a compatible 150cp jet nipple and pricker needle combined with the correct vaporiser for the lantern and with the benefit of readily available jet and needle spares if ever needed.

    On the left, the Petromax nipple mount cut off, Hipolito on the right.

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    I machined a recess in the Petromax component to positively locate it on the Hipolito vapouriser as an aid to silbrazing.

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    A ‘dry’ run for fit before silbrazing.

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    Silbrazing completed, Petromax nipple installed.

    77DEC2BA-2395-418D-8097-69E3F85EB406.jpeg


    Vapouriser back in the lantern. A single prime was sufficient now and no glass scorching!

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    John
     
    Last edited: Aug 2, 2020
  2. MYN

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    That was a state-of-the-art surgery, @presscall .
    However, I find it somewhat hard to comprehend on how would a beefier vaporizer with the slightly larger loop(Petromax) scorch the glass on the Hipolito. I'd suspect that the jet with the hypodermic needle insert was a little too large at the orifice and slightly over-fueling the burner. I've experienced on some of my lanterns and noticed that richer burns tend to produce more radiant heat (probably more infrared emissions) as compared to properly functioning ones. And they do heat up the glass and surroundings more than desired, while producing a slightly dimmer or a more yellowish/orange/reddish hues.
    I'm not sure if this could be similar for your Hipolito with the hypodermic jet.
     
  3. presscall

    presscall United Kingdom Subscriber

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    Ah, no.

    The glass had already been scorched with the Petromax vapouriser/jet/needle combination. The lantern came to me with the globe unmarked. My test firing with the ‘hypodermic’ Hipolito jet was momentary (seconds) sufficient to see it was overfuelling.

    The selller said on his listing that the Hipolito jet was well oversized and had installed the Petromax vapouriser, jet and needle. He’d taken a photo of the lantern lit and fuelling well, which appeared on the auction listing. He’d evidently run it just for that snd thr globe hadn’t been scorched for thst short duration of exposure.

    I’d run it for a couple of hours before I became aware of the scorching of the globe.

    Preston loop outer diameter (Hipolito) = 52 millimetres. Outer diameter of the Petromax Preston loop = 60mm. Inner diameter of globe = 70mm.

    I’m supposing that radiant heat reduces as a factor of the square of the distance as with light? In which case the 5mm clearance between the Petromax vapouriser loop and the inner surface of the glass would have resulted in a lot more heat impinging on the glass than is the case with the 9mm clearance the Hipolito loop provides.

    Inevitably, there’s an inexact clearance between loop and glass, so the ‘hot spot’ would have been where the loop was marginally less than 5mm separated from the glass.
     
    Last edited: Aug 2, 2020
  4. presscall

    presscall United Kingdom Subscriber

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    Curious thing, the air gap to the J-tube with the Hipolito nipple installed on the Hipolito vapouriser was this.

    C2BF1566-4D02-4D0C-B99C-A5AD9FA7F664.jpeg


    With the Petromax nipple on the Petromax vapouriser it was this.

    7CAB8900-7862-4A32-AD37-E4E858CA4CDC.jpeg


    With the Petromax nipple installed on the Hippolito vapouriser it’s this.

    BD3F035A-CF00-4718-928A-EB802126883D.jpeg


    I was expecting to shorten the Hipolito vapouriser to get the air gap correct but was surprised to find that fuelling’s excellent.
     
  5. JEFF JOHNSON

    JEFF JOHNSON United Kingdom Subscriber

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    Well fettled!:thumbup::thumbup:
     
  6. ROBBO55

    ROBBO55 Subscriber

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  7. MYN

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    Glad you had it sorted out. Was well documented. :thumbup:
     
  8. george

    george United States Subscriber

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    Great, John!! Nice job.
     

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