Prabhat #2 resonance problem

Discussion in 'Fettling Forum' started by nokey, Aug 11, 2008.

  1. nokey

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    Hello everyone,

    Recently, I bought a new "Prabhat No. 2" stove from the STUGA-CABAÑA webshop, which came with a number of problems (missing parts, bad pump(well known with Prabhat), leg holder soldered on crooked) which I have thusfar solved myself.
    There is, however one last problem for which I would like to call on your collective expertise:

    When I run the stove I get a sort of "resonance" in the amount of gas that comes out of the jet.
    This can be observed in sound as well as watching the flame. On very low pressures you can actually see the flame come down a few centimeters.
    This appears to be independent of the amount of fuel present in the tank, since I've observed it with 0.5 and 1.6 liters of fuel in it.
    At some pressures this resonance is eliminated.
    First I thought there might be a small leak in the fuelpipe, adding tiny amounts of air to the oil mixture but I have now asserted that this is not the case.
    When I put a piece of cotton cloth in the fuel pipe to dampen any resonance, the problem disappeared.
    This, however, added its own problem, namely that changing the pressure in the tank would get a delayed effect on the flame output.
    I am thinking that putting some fine copper or brass wool in the bottom of the burner and the pipe leading up to it would probably also help to stabilize the jet output but this time without adding a delay on the jet output.
    My problem with this is that I cannot find any company that sells copper or brass wool in the Netherlands.

    Another possible cause could be the type of fuel I use: I use is a very pure type of paraffin lamp oil with a carbon range of C5-C20 (it's very cheap and readily available) with approximately the same flame point as petroleum (> 61 C).

    If any one of you knows an online seller of copper/brass wool or has another idea on how to fix this, I'll be happy to read your replies.

    Regards,

    NoKey, the Netherlands.
     
  2. Doc Mark

    Doc Mark Subscriber

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    Greetings, Nokey,

    Have you given thought to using a fine brass mesh screen, all rolled into a tube and inserted into your fuel line of the burner? Optimus has done this on some of their stoves, and this might be the solution to your problem. And, since it's a mesh screen, there should be little, to no, time delay in fuel vapour making it up to the burner. Just a thought. I, too, have one of those Prabhat stoves, and also a lantern, neither of which I've had time to use. Best of luck with yours, and God Bless!

    Every Good Wish,
    Doc
     
  3. nokey

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    The problem with brass mesh is the same as with brass wool: can't get a hold of any :(
     
  4. Bom Bom Bom Bom

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    Hi,

    Try "The Mesh Company" - google them. They are UK based and also have a UK ebay shop. They sell woven wire mesh in various materials. I recently bought some brass wire mesh (20 weaves per inch is around the average that I've found used in 96 and 100 type stoves) from them and had a thoroughly good experience. I bought 4 x A4 sheets of brass mesh via ebay and they sent 6 sheets as they have a buy two get one free offer on their normal web site. Bought it around 3pm one afternoon and it was through my letter box by 8am the following morning. Really can't ask for better service than that!
     
  5. nokey

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    Outstanding!
     
  6. nokey

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    Oh bugger, they only ship to the UK it seems :(
     
    Last edited by a moderator: Jul 2, 2015
  7. nokey

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    I found another UK Ebay seller who also sells mesh and who does ship to the Netherlands.
    His Ebay ID is "alans3729", for those who want to know.

    I will keep you apprised of my progress.
     
  8. Stonehopper

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    Nokey, if you have no success with shipping direct from the UK supplier, I'm sure one of us Brits would be happy to receive the goods on your behalf and forward to you for the cost of postage for one off small items.
     
  9. Stonehopper

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    I should have added, I have the same resonance from the big Primus No.3 with Prabhat burner. I too thought of it being caused by a back pressure air wave being created within the comparatively large diameter fuel tube, and wondered if a damping material might stop the resonance. I would be quite happy to put up with a slight delay in flame control for a smooth burn. Under high pump pressure the 'pulses' are approximately seven to ten per second, and slow with reduced pressure.

    Be interested in your results.
     
  10. nokey

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    That's OK, the goods should already be on their way to the Netherlands.

    But thanks for the offer anyway.

    NoKey.

    P.S. When I have this beast up and running to my liking, I'll make two post in the reference forum:
    One for a Prabhat #1 with roarer burner (imported one for a friend of mine), and one for my own Prabhat #2.
    And I'll make a post to identify my other parrafin stove, which has no markings of any kind.
     
  11. nokey

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    The mesh arrived here last friday, and today I've done two burns:
    - One with the mesh stuffed in the burner/pipe leading up to the burner.
    - One with the mesh stuffed in the fuel pipe of the tank.

    The first option did not appear to have any effect on the "motorboating" effect (I believe that is the term used for this effect?).
    The second option only seemed to make things worse.
    So I'm back to square one here. Anyone have another suggestion?

    On a side note: today I picked up a new set of leather pump cups from the post office, made by "sefaudi". I've got one soaking in olive oil atm, and I'm very eager to try that one out tomorrow.
     
  12. shagratork

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

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    Hi nokey

    Any chance of some photos?
     
  13. nokey

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    I posted pictures of my Prabhat #2 here and the pictures of my mystery stove here.

    The Prabhat #1 with R1 burner will have to wait since it's not currently here.
     
    Last edited by a moderator: Jul 2, 2015
  14. nokey

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    I also installed the new pump leather.
    It works a lot better than the factory-supplied one I must say.
     
  15. nokey

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    I have also found that putting a small bit of rubber tubing behind the pump cup assembly improves the pump performance by about 200%.
    Behold the simplicity of this:

    1218976586-pompstang-verbetering.jpg
     

    Attached Files:

    Last edited by a moderator: Jun 26, 2015
  16. David Shouksmith

    David Shouksmith Subscriber

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    Brilliant idea, nokey - simple but effective...
     
  17. oops56

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    Yep got some pumps rods that have a small rubber washer behide leather on the small rod just so that it floats then on the down push it seals it
     
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  18. nokey

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    Stonehopper,

    If you're willing to put up with the delay, you can take a piece of pure cotton cloth (simple weave, no stretch) or linen, roll that up tightly and stuff that into the fuel pipe of the tank.

    Best of luck with that, while I ponder other solutions.

    NoKey.
     
  19. nokey

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    Yesterday I tried the stove with the "proper" fuel i.e. paraffin with a C12-C15 chain size, and this seems to mitigate the "motorboating effect" to a certain degree.
    Another notable effect was the higher caloric output of the burner. Even on "low" the heat at 50 cm from the burner was rather toasty. So much that I did not dare pump it up to high in my kitchen.
    I'll take it outside later and see what happens when I pump it up high.
     
  20. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi, resonance, which leads to pulsing of burner flames, can be a feature of pressure stoves of any size. However, it is more often experienced in stoves with large burners.
    If you study Primus Catalogues you will see that orifice plates,or brass mesh rolls which act as flow restrictors are shown for many stoves. These are generally located at the base of the burner itself.
    Yesterday I had the burner off my Primus No.3, 7-pint, roarer burner stove to renew the heat-proof washer. I also removed and cleaned the flow restrictor, so had an opportunity to examine it in detail.
    The restrictor takes the form of a tightly-rolled wad of brass mesh, about one inch (25.4mm) long.
    The mesh is identical to that used in the lipstick vaporisers of types 96 and 100 stoves.
    This "restrictor" is a tight fit in the base of the burner.

    Hope this helps.

    Best Regards,
    Kerophile.