Pump tube/NRV assembly

Discussion in 'Fettling Forum' started by kerophile, Mar 13, 2010.

  1. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi, there are a few fortunate classic stove enthusiasts who never see the rear side of an air pump. Their non-return valves (NRVs) are never irretrievably stuck, and are easily extracted from the interior of the pump tube using the appropriate tool.

    This post is primarily for these lucky people, and illustrates what is on the hidden side of an air-pump. This is what is revealed once the air-pump is de-soldered from the tank and then further dismantled:

    Air-Pump-and-NRV-1.jpg

    Air-Pump-and-NRV-2.jpg

    Air-Pump-and-NRV-3.jpg

    Air-Pump-and-NRV-4.jpg

    Air-Pump-and-NRV-5.jpg

    Air-Pump-and-NRV-6.jpg


    You will note the lead washer designed to be inserted between the head of the NRV and the base of the pump-tube. This is often absent from stoves, and this is part of the reason why NRVs seize in situ. This lead washer spreads and seals on tightening and there is a groove on the base of the pump tube to help accommodate and locate it.

    Happy fettling.

    Best Regards,
    Kerophile.
     
  2. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Wonderful post, George. Pretty chewed example of an NRV valve head there.

    You've rightly mentioned the purpose of the lead washer, but what's your view of the more modern alternative of a plastic washer?

    John
     
  3. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi John, The kindest reply is often silence.....and I believe that Optimus does now supply polymeric washers with new NRVs.

    However, any plastic material used as a washer for an NRV on a classic stove has to be deformable to the extent that it can flow into and fill the circular groove on the base of the pump, to be fully effective IMO.

    If it doesn't deform to that extent you may still get a seal but over a much reduced surface area. The arguments are similar to those when considering the use of "O-rings" rather than proper flat ring-type nitrile washers on filler caps.

    I continue to make and use lead washers.
    Just my teo-pennyworth.
    Best Regards,
    Kerophiel.
     
  4. teletim

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    Hi George,

    Now that you have removed the NRV,reassembled it with a new washer would you reuse the valve with the mashed in head or just replace the whole NRV with a new one?
    I think the few NRV's that I have had to wrestle with to remove had no lead washer.

    Cheers Tim
     
  5. lanevitt

    lanevitt Subscriber

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    I have a Burmos 21 that leaks fuel from the tank into the pump tube. I repalced the tired looking lead washer with a homemade polythene NRV washer.
    I still had the problem. So i made another, replaced it again and still leaked. Made a double washer but still no luck. The fuel was creeping into the pmp tube. Its back to making a new washer from a sheet of lead. OR its just my bad handywork !!!
     
  6. nagant

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    did you replace the pip and spring Andrew ?
     
  7. brassnipplekey

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    OR ... Theres a split in the pump tube ... OR .. theres a leak between pump tube & the pump tube bottom , the piece that the NRV screws into .

    Bloody stoves .. Who'd have 'em ? :-)

    Nick
     
  8. idahostoveguy

    idahostoveguy R.I.P.

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    Very nice George. It is nice to see the details of the pump tube and NRV together. I didn't realize the end of the pump comes apart like that. That for show that and the nice pics!

    Thanks,
    sam
     
  9. theyellowdog

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    I have had the pump tube out of my burmos 55 3 times now trying to stop it from leaking. Driving me up the wall! Will get it fixed in the end. All good practice I suppose.
     
    Last edited by a moderator: Jul 2, 2015
  10. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi Tim, I try to recover NRVs when I can, but by the time they come to me the top sections are usually worse then the one in the photos. I believe that you could try re-building up the damaged sections with braze metal and re-shaping with a file; but I have never tried it.

    I used to have a few spares but I am now down to NRV parts, and I have never seen the tops offered for sale separately.

    A new NRV from Base Camp now costs £11 (US $16 approx.) plus shipping, so the cost of fettling stoves can soon mount up.

    Best Regards,
    Kerophile.
     
  11. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi Andrew. Once I have repaired a pump-tube NRV, I test it out in a glass if water so I can see that it is pumping air and not sucking back, or leaking from a solder joint of crack in the tube itself. If it pumps air well, and there is no water getting into the cylinder, I re-solder the pump into the stove tank.
    If you think it ia a faulty gasket I can send you a few lead washers to try.
    Best Regards,
    Kerophile.
     
  12. teletim

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    Hi George,

    Thanks for the reply.
    I would like to have a bash at reshaping the head of a NRV that is rather mangled up.

    Mashed_NVR_opt.jpg

    I have not done any brazing yet and I think this might be by good first project.
    I have torch on it,s way to me.{the one you sent the link over}
    What type of solder would you recommend to braze and reshape the head of the NVR?
    The flux i use for soldering should be OK I think?

    Regards Tim
     
  13. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi Tim, I would try a "silver solder" first, and you will need to buy a special brazing flux appropriate to the braze metal you inend to use.
    The NRV top piece will need to be really clean before you start to braze. I use a citric acid pickle and give it a good scrub before even thinking of brazing.
    Best Regards,
    Kerophile.
     
  14. lanevitt

    lanevitt Subscriber

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    Hi George,

    The offer of some NRV lead washers would be most welcome, thankyou! i do have some lead around the farm but can i find the damn stuff!! I think de soldering the tube assembly and aproaching the repair from both sides would be more thorough. that way i can also water test the end job as you have written.

    Please let me know the costs of the little devils and i will arrange payment, as usual.
     
  15. barrabruce

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    I've often wondered if making a flat srewdriver slot would be easier all round on the mangled ones.

    Probably just as cheap to buy some junker stoves for the parts ..but then you fix 'em .. and buy more ... :doh:

    Postage is the killer thou.

    Barra
     
  16. RonPH

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    Making a screwdriver slot on brass will mangle it further in the sense that the brass wall becomes thinner. Rebuilding it as Lance has mentioned is a better option and makes it even sturdier since silbraze is harder than brass (so they say). I normally buy the parts (or stove for parts) even before attempting to fix the stove part in question so that if I do f**k it up, I have a replacement on hand. I do not want my stove lying around useless for a long time. I'd prefer it up and running in no time.


    Ron
     
  17. teletim

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    I have now cleaned up the NRV head ready for brazing.
    I have ordered appropriate solder and flux to reshape the head.
    So now with a bit of practice I should be able to make this NRV usable again ........ we will see!

    Mashed_NRV__cleaned_up.jpg

    Cheers Tim
     
  18. lanevitt

    lanevitt Subscriber

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    Hi Tim Brazing is easy...After a few trial goes you will be a master... If you can solder such good joints, like you have shown, then you will have no problem.

    Please post your handywork..
     
  19. teletim

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    Hi,

    Today I received my torch and silver solder kit.
    Pic1.jpg

    Pic2.jpg

    What I intended to do was rebuild the corners of the NRV head which had rounded of when removing it from the pump tube by building them back up with solder.

    Pic3.jpg

    Tooth paste is great for protecting the threads......... Cheers George.

    Pic4.jpg

    You can see the fist corner filed and rubbed down,I am now working on the second corner.

    Pic5.jpg

    After rebuilding up the corner a clean up of the solder and trimming the head up bit by bit I have a good tight fit to the NRV spanner.

    Pic6.jpg

    I think the effort to try and rebuild the head was a worth while project I have a few more to do that are in a worse condition ............. builds on the soldering and brazing skills.
    The red rash on the back of my thumb is were I burnt it with the torch :shock:
    I am stuck on the type of solder I need for this type of work,the kit I bought was for brass and copper,however it was expensive any suggestions?


    Cheers Tim
     
  20. RonPH

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    Tim, thats a great job you have done :thumbup: At one time or another, working with stoves or fettling them especially with torches, sometimes you do get singed however slightly. As far as other materials used, I really have not used any except the silbraze 56% wire, white flux, and mapp torch although my torch puts out a lot of heat. If I could just find a mapp torch with pencil flames for more precise heating.

    Again congratulations.

    RON