Primus Omnifuel - Lightning does strike twice

Discussion in 'Stove Forum' started by JonD, Aug 18, 2012.

  1. JonD

    JonD United Kingdom Subscriber

    Offline
    Joined:
    Aug 18, 2012
    Messages:
    286
    Location:
    Hertfordshire, England
    Hi - new to forum, I wanted to share some info about my experiences with a pair of Primus Omnifuel Stoves I have been running on petrol (Gasolene for US).

    They have both suffered the same highly dangerous failure hence the title of this post.

    Usually in dismal weather when you really need Coffee Now! = Now! and the wind is so bad that the likes of Coleman Sportsters just won't stay lit, the seals on the fuel line fail and spew out Gas ready for a super fireball.

    The last occurrence of this included the seal on the tank fuel control valve as well so Gas was coming out pretty much everywhere.

    My first experience of this, on a camping trip, the Omnifuel was the only stove I had and there was nowhere to buy spares. Instead I bought another complete stove resolving to fix the other one at some point - then I would have two! SWMBO did not mind buying a new stove in the interest of hot coffee - neat trick.:content:

    Best I could do with the repair of #1 was to buy a complete fuel line/Valve assembly. I was told the parts are not available - mmm maybe Y/N....
    Anyway - not cheap but quick and easy.

    This time on #2 I was not going to part with that kind of money again - I was going to fix the old one no matter what. Looked at the spares section of Primus website, a complete service kit was the only offering. It contained all sorts of bits I was never going to need. Also it was not far short of the price paid for the fuel line+tap 7yrs ago. No,I wasn't going that way.

    Fixing the Control Valve seemed easiest to tackle first. It needs an adjustable spanner since the nut is 8.5mm AF - it maybe some exact imperial size but I had nothing to fit. The spanner needs thin jaws otherwise they won't fit under the head of the control valve - mine is 5.5mm - about the max. Once the nut is undone the control valve screws out and the rubber sealing washer at the base was obviously very flat and very hard. Here's the trouble - not sealing.

    Getting the fuel line out of the valve head is harder work. It's held in by soft copper wire that jams in a slot. I could find no better way than brute forcing it by levering on both sides (to maintain steady perpendicular force on the nipple) Eventually the wire is forced out of the slot and the thing comes out. The rubber sealing washer on the base was in exactly the same state as the one on the control valve.

    Now to find some O rings to replace them. Nothing in the usual box of mixed rubber O rings as available on ebay etc. I tried cutting and joining one with superglue - no good.

    Base Camp UK - my usual source of stove bits - lists what I think is the right part but I know I will have to wait a week or so to get them there. I want this fixed now!

    Research on Internet says Nitrile rubber is OK with Petrol etc. Thats good because most stock O rings are made of that. Presumably if that is what Primus originally used it doesn't last forever but if I have plenty of spares why should I care? I ordered some 1.6mm thick and 2.75mm inside diameter from an online supplier and they turned up next day.

    Fitted to control valve and re-assembled with a little silicone grease for lubrication - perfect.

    Fitted to fuel line and it felt like the seal would be OK - not quite as tight and positive as the control valve but hopefully gas tight.

    Now some means of latching home the fuel line without the copper wire, and at the same time making something that can be disconnected a little more easily for next time - probably in howling wind + rain. Needs a "C" clip of spring steel just the right diameter - of course I don't have any....

    What I do have are guitar strings - hehehe :twisted:

    Take a 5th A string (wound) and cut a bit off the end. Form it into an almost closed C of the required diameter - presto - hose locks home! Give it a firm tug and it comes out again. Might prefer if that tug needed to be even a bit harder than it is now but short of dropping a full fuel bottle while holding the stove it will never get tugged hard enough to come out - this is definitely worth trying out.

    Pump up tank - turn on valves - no leaks!

    Fire up stove make coffee. :lol:
    Think about something else for a better C clip while drinking the coffee. Something will turn up and I will know it when I see it.

    1345305120-DSCN1961.jpg

    Hope this post will be useful to someone since looks like you will probably need to know about this sometime with an Omnifuel. My pair have not been heavily used and are always stored in normal indoor conditions. This is not a question of wear - simply seems 7yrs is about the age this happens. I now have a good stock of the O rings some of which are going into the bits pouch along with Nozzles Multi tool etc.
     
    Last edited by a moderator: Jun 26, 2015
  2. geeves

    geeves New Zealand Subscriber

    Offline
    Joined:
    Sep 29, 2009
    Messages:
    5,184
    Sounds like a good and successful repair. Strange I've never read about this problem before.
     
  3. lanevitt

    lanevitt Subscriber

    Offline
    Joined:
    Jun 27, 2009
    Messages:
    1,605
    I have the very same problem with my Omnifuel fuel line. I never really noticed any leaks until i used a gas canister to find fuel leaking from both ends of the control valve body. I may contact Primus to sort this out as it is a considerably dangerous fail.

    PS.. Nice to be back on the forum, long time no internet !!
     
  4. Vintagetwinshock

    Vintagetwinshock Subscriber

    Offline
    Joined:
    Feb 17, 2013
    Messages:
    251
    Hi,
    Regarding 'O' rings, my suggestion is for someone to accurately measure the one(s) required & feed that information to the fettlebox, with an increased inventory of seals &c, he can then provide an improved world wide service. :content:
    John.

    ---------------------
    If in doubt, brew up.
     
  5. Spiritburner

    Spiritburner Admin Subscriber

    Offline
    Joined:
    Jul 23, 2004
    Messages:
    10,190
    Location:
    N.E. England
    Hi Lanevitt!

    Info that cites nitrile as being ok with petrol needs to be treated with caution as it depends how much nitrile is in the mix. The good thing with Viton is that it is what it is. A Viton washer or O-ring is 100% Viton.
     
  6. theyellowdog

    Offline
    Joined:
    Mar 10, 2008
    Messages:
    1,989
    In my omnifuel on meths thread there is a comment that primus uses neoprene o-rings.

    I do not know if that is correct, however it may be the case. Primus say alcohol can damage the o-rings. I think nitrile is OK with alcohol.

    However the omnifuel has a host of o-rings and they may be made of different materials.

    Does anyone know about neoprene o-rings?
     
    Last edited by a moderator: Jul 2, 2015
  7. emes

    Offline
    Joined:
    Jun 15, 2012
    Messages:
    6
    I'm unable to disassemble the hose-valve connection. I only managed to strip the inner fuel line from the metal connector, but it still stays in the socket.

    By the way, in Omnifuel that valve is absolutely useless. It would me much simpler to have just a straight hose with two connectors: one for the pump, another for the stove.

    Do you have any ideas what are the threads on both ends? I'd like to search and order such a replacement.
     
  8. Murph

    Murph United States Subscriber

    Offline
    Joined:
    May 14, 2010
    Messages:
    2,234
    Location:
    Milwaukee WI, USA
    I'll have to make note of this, that control head looks just like the one on my Classic Trail stove.

    Never mind, same casting, different machining!

    Murph
     
  9. teckguy_58

    teckguy_58 United States Subscriber

    Offline
    Joined:
    Mar 20, 2011
    Messages:
    889
    Location:
    Washington USA
    Hi JonD,

    Great post thanks for sharing.

    I do agree with Ross. Viton O-Rings will hold up better over time. They can be found in any hardware store here in the US in both metric and standard sizes.

    I have a Primus MFS and the pump leaks like a sieve and there doesn't seem to be any way to fix it. I have another pump just like it and it also leaks. Stay away from this pump if you can. Some have had no problems with the same pump.

    1343297422-IMAG0159.jpg

    This is the fitting that leaks. I suppose if one could get the fitting off of the pump and make an adapter the pump would be useable. So far I have been unable to remove the fitting from the pump.

    1343297466-IMAG0160.jpg

    Murph jump on in because I'm sure you have a great idea on how to fix this particular problem. I know I don't.

    Cheers,
    Norman
     
    Last edited by a moderator: Jun 26, 2015
  10. BernieDawg Banned

    Offline
    Joined:
    Feb 23, 2008
    Messages:
    1,656
    To answer your question...
    The attachment thread at the stove is 8mmx0.5 metric.
    The attachment thread at the canister is 7/16x28tpi (UNEF).

    I doubt you can find an alternative anywhere unless you are willing to have a machinist make one custom for you.

    You could try to buy a replacement hose/valve set here:
    http://www.primus.eu/products/spare-parts

    Based on the comments you've made above, I'm going to guess you won't like the price you will pay from Primus. :whistle:

    I like the valve at the bottle because it allows for fine-tuning the flame pattern and eliminating surge in the line. Having a two-valve line almost always results in a stove that has better simmering characteristics. So, I would very much disagree that the bottle-side valve is "absolutely useless". :)

    If such a valve is unimportant to you, perhaps a MSR XGK-EX is a better choice for your needs.
     
    Last edited by a moderator: Jul 2, 2015
  11. JonD

    JonD United Kingdom Subscriber

    Offline
    Joined:
    Aug 18, 2012
    Messages:
    286
    Location:
    Hertfordshire, England
    Thanks for the comments - this thread has livened up again after about 2years or so :content:
    My Omnifuel union is still latched home with that bit of guitar string - I still haven't found anything better - proves I haven't needed to maybe?

    On the leaking pump - I have one of those with the aluminium block body - which I prefer. I also have the plasticky bodied one which came later. Touch wood I have had no trouble with either but I think I know what probably leaks on that aluminium one.

    Inside the knurled aluminium will be another O ring - most likely Nitrile again and it will have hardened off in the same way. Again it is held home in the joint by the aluminium having been "peened" over - the brass in the fuel hose joint I reckon was probably pressed over the C clip, post assembly, in just the same way.

    You can do things like this with production tooling and jigs that exert massive forces. Very hard to undo such with hand tools at home.

    I think with an aluminium part you stand more chance. If you could exert force from inside the lip pulling it outward you could gradually undo the peening until the joint would come apart. It needs some sort of smooth hooked tool with maybe a threaded tensioner to tighten up as the metal is worked outward while rotating the tool gently around the rim.

    I'm not sure brass would let you do this - too brittle. Also the fuel hose connection is only about half the diameter - very difficult to get any sort of tool in there.

    With ally I have managed similar things before.

    Good luck - I expect to need to be here sooner or later.
     
  12. emes

    Offline
    Joined:
    Jun 15, 2012
    Messages:
    6
    Thanks BernieDawg for the data!

    I looked at the Primus website and see a choice of hoses. There's even one which would probably match my expectations:
    http://www.primus.eu/hose-34227
    Still a rip-off, though.

    Unfortunately, there's no info if it would fit my Omnifuel. The absolute lack of basic data and mixing metric and imperial sizes in one product is something I personally hate about that company. How one is supposed to deal with problems while stuck in the middle of nowhere without essential 7/23" and 8.5mm wrenches combined with a set of 20 different o-rings?

    Anyway, I cooked few hundreds of meals on my Omnifuel, and I can say that the stove itself is just great. I did it all using the pump-end valve in only two positions: full-close and full-open. So, for me, the pump-end valve is just excess weight and complication (it even got stuck once).

    Well, I'm going to ask at Primus and see what happens.
     
    Last edited by a moderator: Jul 1, 2015
  13. mirceacroitor

    Offline
    Joined:
    Apr 28, 2011
    Messages:
    17
    I had exactly this problem once this winter, the fuel was leaking from the hose coupling in T connector (the valve was OK - not leaking). It appeared only one time, at -7 degrees C, and I suspected it was the gasket not working because of the low temperature. The problem solved itself somehow after screwing the T more into the pump (strange). I also did some tests at -10 degrees C but the leak didn't happened again. My Omnifuel is only 4 years old now ... I'm still a bit worried about this problem.

    I kindly ask the OP to give more details on how to remove the hose from the T connector near the pump, it seems the most difficult task in the eventuality of a repair there (replacing gasket). The valve at T is simple to disassemble with the included tool. I'm preparing a wounded string guitar for the repair kit ... just need to know how to disassemble the hose.
     
  14. Afterburner

    Offline
    Joined:
    Mar 13, 2014
    Messages:
    1,899
    Hose is not meant to be removable from the connector at the pump end of Omnifuel's fuel hose. You can try to pull out the hose from the connector by using extra force but maybe you don't get it back there anymore.

    My Omnifuel is around 8-10 yeards old and I have used it in -32 °C without problems.

    If that joint starts to leak you need to change the whole hose (or do some DIY repair to it)
     
  15. mirceacroitor

    Offline
    Joined:
    Apr 28, 2011
    Messages:
    17
    The OP's problem shows that hose sometimes needs to be disconnected to replace the gasket and the photo shows that he did it. I just want to know how, to be prepared.

    I used the my Omnifuel 1 week ago at -12, no problem, but ... if the leak happened then, I wouldn't know how to dissasemble it. I don't want to carry a spare fuel line just for that.
     
  16. Afterburner

    Offline
    Joined:
    Mar 13, 2014
    Messages:
    1,899
    I would believe that hose is not meant to be removable from the connector at the pump end of Omnifuel's fuel hose. If it would be removable to change the seal/gasket there would be a nut instead of pressed collar to mount the hose to the connector.

    Just for fun you can remove the hose as it's shown in the pictures above and change the seal/gasket. I would guess that putting it back might be a small challenge (that is only my guess since I have not done it...)

    Anyway, send us some pictures from you seal change project. :D/
     
  17. mirceacroitor

    Offline
    Joined:
    Apr 28, 2011
    Messages:
    17
    I will not disassemble it, only if it leaks again ... "if it ain't broke don't fix it". So no pics until then :)
     
  18. presscall

    presscall United Kingdom Subscriber SotM Winner

    Offline
    Joined:
    Aug 25, 2009
    Messages:
    8,381
    I suppose as our Omnifuels get older there'll be more failures. I never did like being unable to disassemble the connector on the old, aluminium block fuel pump.