Optimus Trapper with home-made 'Safefill' device

Discussion in 'Optimus No:81' started by presscall, Sep 26, 2015.

  1. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @hubert pellikaan said,
    How right you are Hubert concerning the corrosion, although it wasn't so much the Safefill popping out that afflicted an example I bought recently off ebay, but that the Safefill was immovably bonded in the filler tube, prompting a refund of part of the auction price since I opted to keep the stove and work something out.

    After soaking the end of the Safefill bonded to the stove and tugging unsuccessfully (tearing off the filler lip flange in doing so) I'd to lever out the broken plastic remains and get thinking of an alternative

    1.JPG


    The bonding took place between this ...

    2.JPG


    ... and the air inlet/filler tube of the stove here ... (that's the replacement 'Safefill' in position in that photo incidentally and not the original)

    2a.JPG


    I've another Trapper with an intact Safefill and that helped arrive at the dimensions for the replacement I constructed out of brass and 3mm nitrile sheet

    3.JPG


    With the air inlet/filler tube on the stove cleaned up I was glad to find that the stove had sprung no leaks and worked fine

    4.JPG


    Here are my sketches for the filler gadget

    5.JPG


    I made use of a couple of these water tap mandrels, but discarded the plastic tap washers

    6.JPG


    One's silbrazed onto a length of brass rod, a short length of 10mm diameter rod (having a 5mm tapped hole running through it) silbrazed onto that, into which is screwed the second mandrel

    7.JPG


    I encased that second, removable mandrel in nitrile discs, bonded with epoxy - the discs to provide a grip to screw and unscrew the cap and to make a seal with the filler tube to prevent evaporation of the fuel when the stove is stowed away

    8.JPG

    9.JPG

    10.JPG

    11.JPG


    I decided to provide a more robust nitrile cone for the sealing arrangement rather than the fragile O-ring of the original. The nitrile seal is held in place with a tapped brass disc. Thinking about it, I didn't visualise needing to replace the nitrile seal so peened the end of the rod over to 'fit and forget' and not be harassed by the disc unscrewing and being lost

    12.JPG


    The disc (rather than using a hex nut) enabled the necessary clearance for the air control flap to slide into place when the stove is stowed away

    13.JPG

    14.JPG


    To fill the stove, the device is pushed into place in the filler tube - sealing the base of it for the filling operation - and the cap is unscrewed

    15.JPG

    17.JPG


    Fuel is poured in ...

    16.JPG


    ... and giving a few seconds for the wadding in the tank to soak up the fuel, the cap is screwed back on the filler device to remove it from the filler tube. Stove is ready to fire up.


    This is where the Trapper comes into its own, controllable from a simmer ...

    18.JPG


    ... to a scorcher of a flame, should it be needed

    19.JPG

    John
     
    Last edited: Sep 26, 2015
  2. idahostoveguy

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    Very creative and inventive fettle. Should go a lot longer and with the replaceable parts work for a really, loooong time!


    sam
     
  3. jbf

    jbf Subscriber

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    Impressed :thumbup:
    Very Impressed
    Actually very very impressive
    i applaud your efforts :clap::clap::clap:
    john
     
  4. junior trangia master

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    :lol:
    nice thinking.

    archie
    10 years
     
  5. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Thanks Archie, Sam and John.

    John
     
  6. Rangie

    Rangie Subscriber

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    What a piece of kit. Its caused much thought over the past 24hrs.
    From the operation of the stove and the dry/fill weights, to the calculated volume of fuel the mass can absorb and not weep in use.
    It must have caused a few sleepless nights for the designers! :mrgreen:

    Alec.
     
  7. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    You're right there, Alec. Filling it to the point where the fuel starts to weep out of the fill-level hole is the equivalent of getting the fire-proof wadding saturated up to that level, which corresponds to the top of the raised lip at the base of the central vent tube that the Safefill pushes into.

    John
     
  8. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    The raised rim at the base of the filler/vent tube is obvious in this diagram

    image.jpg

    In the case of the earlier Trapper without the fill-level plug arrangement it was easy to misjudge re-fuelling and take the fuel over that rim. In an outdoor location it would be only too easy to overlook the overfuelling and ignite the spillage.

    It could be managed by filling the Trapper on a 'tell-tale' rock or paper that would show the pooling of fuel under the vent - so that becomes the overfuelling indicator - then moving the stove somewhere away from the spilt fuel to light it once it's stopped dripping. Not as convenient as having that fill-level plug at the side however.

    John
     
  9. orsoorso

    orsoorso Subscriber

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    Unfortunately, with the early type, there was almost no space between the absorbent matter and the bottom.
    So, even you did apparently not overfill, when you light the stove, the absorbed alcohol expanded, and if excessive for the retention capacity of the absorbent, pour below, ignited, with the consequences you may figure.
    The only way to safely refill the early Trapper 81 is tho burn it dry and use the measure, or, as I have personally done until I got a new type Trapper, carry one of those cheap chines electronic scale, and fill at the weight before checked, filling a dry stove with the measure.
     
  10. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Good point, Orsoorso, I guess you're referring to those radial grooves in the bottom of the newer type that the original version didn't have.
     
  11. Doc Mark

    Doc Mark Subscriber

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    Good Morning, John,

    This is a superb tutorial on how to make an updated replacement for the more than a little fragile "Safe-fill" device that Optimus originally shipped with these wonderful stoves. VERY well done, and much appreciated!!! IF you ever decide to make these for sale, please put me down for two, and I'll send payment right away.

    But, until then, I may try my own hand at making something similar. Your design idea is excellent, and maybe I can tweek it a tad so I don't have to silbraze anything..... as that's not a skill I have yet obtained.

    One question, however: Have you had problems with the Safe-fill before, or is this the first time one has bonded like you showed us? I've been using them for many years, and other than having to lube the o-rings very often, which I consider regular maintenance, and having the o-rings break now and then (VERY thin stock!), the only other problem I've had was that the cap on one of my Safe-fill devices broke off after many years of use. In use, I never actually leave fuel in my Trapper stoves, once we're finished using them, but rather, let them burn out, and then capping with with the Safe-fill (o-rings properly lubed, of course). How long had the Safefill been installed in your Trapper, for it to become bonded like that, John?

    In any case, HUZZAH to you for yet another very clever, and very inventive replacement/upgrade for one of our stoves, in this case, the wonderful Optimus 81 Trapper!!! Take care, and God Bless!

    Every Good Wish,
    Mark

    P.S. Darn it!! Now I'll have to go down into the Hobbit Hole, and dig out the 81 Trapper we last used, just to "make sure" it had no fuel left inside it!! Also, I will check to see if the Safe-fill is bonded to the aluminum, as was yours! I'll report back here, after checking it out. We last used that stove at CASG #3, which was back in 2010!!! IF I left fuel in the Trapper tank, it's either evaporated out, or quite possibly, bonded my Safe-fill, like yours..... More, after I check this out.....
     
  12. orsoorso

    orsoorso Subscriber

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    Exactly Presscall, those groves (seen from outside) are, from inside (quite obviously) ridges, on top of which the absorbent rest.
    I attempted to upgrade the old model, fitting a threaded rivet on the side, close to the bottom, but it didn0t worked.
     
  13. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @Doc Mark

    Hi Doc and thanks for the feedback! On the matter of making up parts for sale, it's not something I've got around to doing - like you, too much to do, too little time and keeping someone waiting at my pace on a commercial footing isn't something I could tolerate, even if they could. That said, when time permits I've been known to make something up for a stove chum as a gift, so keep an eye on the mail, hopefully this side of Christmas.

    I've no way of knowing from the seller how long that example had taken to seize up in that way, but the Trapper I already had (the earlier version without the fill-level plug) hasn't done so or shown signs of going bad. It was good when it came to me and I've kept it so as you have yours.

    I think what might have happened is that the Trapper was kept for many months orientated base down, soaking in fuel. If hung up by the stuff sack cord so the stove was suspended on its side, or sat on a shelf in the stowed manner (fry pan at the top, burner base uppermost) that wouldn't have occurred I'm sure.

    Why the corrosion? Drawing on my school science, aluminium corrodes as a non-permeable surface oxide that seals the bulk of the metal beneath from air and damp. In the Trapper that oxide formed in the fuel-rich, damp conditions and although the metal underneath the oxide is still sound (fortunately for me) the aluminium oxide - white substance in the photo of the affected Safefill tube - was sufficient to bond Safefill-to-stove. What I'm not sure of (@kerophile @orsoorso) is the metallurgy/chemistry in relation to any or no alcohol fuel reaction to aluminium. Is it the fuel, or water in the fuel, that combined with air causes the corrosion? Or both fuel and water content reacting (with air) with the aluminium?

    John
     
  14. orsoorso

    orsoorso Subscriber

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  15. pysen78

    pysen78 Subscriber

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    My guess is that methanol caused the corrosion. Seems to disagree with many alloys.
     
  16. shagratork

    shagratork United Kingdom Moderator, R.I.P. Subscriber

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    The first Trapper that I saw was owned and operated by Nick (brassnipplekey).
    I was very impressed. It seemed to be a Trangia with all the extras that you wish the Trangia should have.
    I thought, 'I must have one'.
    But they are not easily available and the usual costs are high.
    I should have bought one them years ago because they are even more expensive now.
     
  17. Doc Mark

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    Hey, John,

    I will let you know how things look when I can dig out my 81 Trapper, and if corroded and bonded to the aluminum, I'll post photos here. Many thanks for your always precise comments and replies, and for your always sharing spirit. I'll be dropping you a PT soon, and we can discuss your kind offer further. Take care, my friend, and God Bless!

    Every Good Wish,
    Mark
     
  18. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Cheers Trevor and Doc and thanks Orsoorso and Pysen.

    I've taken a look at that thesis, which is very interesting. Alcoholate corrosion? I don't think so. The effect of whatever was happening on the metal at the base of my Trapper's fuel filler tube/vent doesn't resemble the characteristic pitting as pictured in the paper and there was no pitting or damage once I'd cleaned off the white 'oxide'. Neither did the formation of the oxide have heat (it formed with the stove in storage and not in use) or pressure as contributory factors, unlike the automobile engine applications referred to in the thesis in the context of part-bioethanol fuels.

    What I've learned from that paper though is that what I described as aluminium oxide was most probably aluminium hydroxide, Al(OH)3, suggesting a reaction to water in the fuel and damp storage conditions, consistent with rusting of the clasp of the stove's Anho strap.

    John
     
  19. patatwin

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    I think you're right. Methanol is rough with many materials, especially with alloy...
     
  20. hubert pellikaan

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    I always used Ethanol at 86% or 94%, where the rest is water. Ethanol is very hygroscopic; with methanol I dont know if its as bad as with ethanol but the OH group is the same, so I guess it is an issue there too. So with my stoves the issue was water-caused for sure. Anodized Al has this issue a lot less!
     
    Last edited: Sep 29, 2015