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Locomotive Front End Designs

Discussion in 'Steam Traction' started by ragl, Feb 19, 2016.

  1. jma1009

    jma1009 Active Member

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    With a chimney length above the choke less than 2 x choke diameter, the chimney sucks in air at the top of the chimney into the smokebox. That is one failing of the Stanier drawings supplied by Courier.

    Sam Ell used to delight in showing this with certain locos on test on the Swindon Plant holding a lighted cigarette near the top of the chimney. The fag smoke was drawn into the smokebox.

    Now, if a chimney is drawing air in from the top then surely it is not working correctly? Neither of Courier's drawings from the Inst Loco Eng of the Stanier arrangements satisfy the Ell formulae, and do not satisfy the Jos Koopmans formulae.

    Cheers,
    Julian
     
    Last edited: Jun 2, 2016
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  2. jma1009

    jma1009 Active Member

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    As a bit of an aside, in 1904 I think, Churchward worked out 10 'standard' smokebox draughtings using the then recent Goss results plus a few tests of his own (I think Holcroft worked these out for Churchward but I need to go back through my notes). These were used till the late 1930s when Sam Ell started his research - which came to prominence in the 1949 onwards BR testing at Swindon and Rugby. Jos has quoted Young at Illinous in the 1930s, which I have no doubt Ell was aware of. The GWR Manor didnt fit in with any of the standard 10 smokebox draughting arrangements and suffered as a result till Ell transformed them in the early 1950s, as he did to the V2s and many other locos.

    Incidentally, and off topic, the reference to LeMaitre on the SR and Brighton by Spamcan81 is a diversion. Bulleid did not fully understand smokebox draughting, hence reference to this on other threads.

    It is not sufficient to say the Stanier Duchesses had an excellent boiler so in effect the smokebox draughting didnt matter or tweaking of same couldnt have affected a marked improvement. The same could be said of the Bulleid pacifics as originally built.

    Cheers,
    Julian
     
  3. Courier

    Courier New Member

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    Ell was a very good engineer - read his paper on solving problems on diesel hydraulics to see how well he dealt with things outside the traditional comfort zone of steam locomotive engineers. However I don't think he worked out his front end from first principles - rather he saw how good the Dean Goods was, had some understanding of what made it good - and applied a scaled version of that front end to other engines - starting with the Ivatt 2-6-0.
     
  4. std tank

    std tank Part of the furniture

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    ie on the Ivatt, a taller chimney with a smaller diameter throat. No alteration to the blast pipe.
     
  5. Courier

    Courier New Member

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    2MT F04.JPG
     
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  6. Courier

    Courier New Member

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    following give an indication on front end design at Swindon in early part of 20th century
     

    Attached Files:

  7. Jimc

    Jimc Well-Known Member

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    In
    People sometimes seem to assume that the Dean Goods front end dates back to the 19thC, but it seems to me that must be wrong.

    Even if you discount changes in the smokebox with the introduction of superheating before WW1, the Swindon drawings list on the NRM website suggest a lot of work on smokeboxes on many classes around 1921, and boiler changes at least on the Dean Goods in the 30s and 40s.

    So to me that suggests that the Dean Goods front end that Ell used as a reference point was developed from the Goss/Churchward work, and probably refined yet further in the early 40s.

    Happy to be corrected by those who have studied more though.
     
    Last edited: Jun 5, 2016
  8. JJG Koopmans

    JJG Koopmans Member

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    I am inclined to discuss this, but would like to suggest to split this off into another thread. The class 2 front-end and views of the early
    twentieth century have little in common with the present P2 thread.
    Kind regards
    Jos Koopmans
     
  9. Big Al

    Big Al Resident of Nat Pres Staff Member Moderator Friend

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    The above posts are a spin off from the P2 thread for further discussion of this specific topic.
     
  10. johnofwessex

    johnofwessex Well-Known Member

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    From my very limited understanding of the subject - see also the Thompson thread & the discussions around working on a GWR Pannier Tank, David Wardales comment about the steam locomotives worst enemy being its proponents who never designed them properly seems to sum up the situation rather well
     
  11. MarkinDurham

    MarkinDurham Well-Known Member

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    I concur with others - this thread is fascinating, not boring. Thank you.
     
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  12. JJG Koopmans

    JJG Koopmans Member

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    Wardale may be right, but who is to judge right or wrong? Even unexpected bad outcomes of tests are scientific proper results.

    As for the earlier Swindon papers, they really show how deep the people in Swindon were into the findings of Goss. Some of it should be taken with a grain of salt, but this was part of the development of a proper exhaust system anyway.

    As for the improved LMS class 2 chimney of 1950 shown above, that is what it is all about! Proper dimensionless ratios shown all over. If you want my comments, the distance between orifice and chimney choke has the notion "not critical" Imho this is only true in connection with a proper (bellmouth) chimney entrance as the diameter of the jet, six orifice distances away of the orifice, is about equal to the chimney choke diameter and should not miss it!
    The chimney length -diameter ratio has the notion 2.33 D minimum. I find this amazing as Ell in his later publications gave 26 inch as
    minimum dimension, so a fixed dimension instead of a ratio. My own analysis of the Rugby data showed decreasing performance with
    a length diameter ratio from 2 downwards and in case of the 1.55 of 6023 draft was finished.
    Kind regards
    Jos Koopmans
     
  13. Allegheny

    Allegheny New Member

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    I agree it's a fascinating subject.

    Please correct me if I am wrong, but the original exhaust on 71000 was a double chimney based on the Dean goods (or two Dean goods!). Therefore. based on the above discussion, correctly proportioned but it didn't work.

    This was replaced by the double Kylchap, which did work. My theory is that the original was reaching sonic velocities, which doesn't make the best use of the energy in the exhaust steam.
     
  14. JJG Koopmans

    JJG Koopmans Member

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    A copy of the Rugby Test report (#15) is in my possession, it shows 6 psi as max back pressure while the MN in its report showed 8 psi.
    If I look at the front-end drawing which is also in Nocks "The British Steam Railway Locomotive" fig. 350 it shows a orifice to choke distance ratio of 7.5 which is too large. The 4 inch orifices should be ok since it is a three-cylinder locomotive and as such are smaller than Ell's formula prescribes. I have severe doubts about the double blast pipe casting since it is very narrow at the bottom. All in all room for improvement which the Kylchaps provided.
    Kind regards
    Jos Koopmans
     
  15. Courier

    Courier New Member

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    The standard BR front end (used I think on all the Std locos) was pretty much a scaled Dean Goods. That is not a bad thing - diverse modern locomotives such as the V2 and the 2MT had been transformed by being given a "Dean Goods" front end. So fitting a double chimney version of it to 71000 was quite logical. Perhaps where Ell could have done better was......

    - his formula for scaling the dimensions was based off heating surface (if I recall correctly) - and perhaps on a locomotive such as 71000 with a large grate but relatively modest boiler dimensions that formula led to blastpipes which were too small.
    - When working on some other locomotives he had fine tuned the dimensions by testing different prototype designs before settling on a final design - perhaps it would have been better if 71000 had been built with an easily changeable blastpipe and chimney.

    I have no idea if the poppet valves required a different form of front end (Kylchap) - and don't think it is fair to assume that Ell should have anticipated that.
     
  16. pete2hogs

    pete2hogs Member

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    I've dealt with that myth before. The A1/A3 Pacifics always had frame problems, it was not related to power but to flexing on a relatively unsupported part of the frame. It is covered in detail in the Green Guide.

    However gently FS is used it is likely to crack them again. Because they all did.

    If anything in FS's preservation history exacerbated the problem it was probably some of the yard layouts it was asked to negotiate. Mind you, I don't suppose any of them were much worse that what could be found around Kings Cross - but its yard mileage to running mileage ratio would presumably be a lot higher.
     
    Last edited: Jun 6, 2016
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  17. Courier

    Courier New Member

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    Thinking back to the earlier comments comparing the Stanier Pacifics with Gresley Pacifics. The performance of the locomotive doesn't just depend on how efficiently you can get smokebox vacuum - it depends on the resistance of the ashpan/fire bed/boiler - ie how much smokebox vacuum do you need to get the right amount of airflow. That depends on the design of ashpan/firebox/boiler and the type of fuel (say coal in big clean lumps in 1930 or dusty small lumps in 1950).

    I *think* it is correct to say that a single chimney Stanier Pacific steamed better than a single chimney Gresley Pacific - the latter needed the advantage of the Kylchap to overcome poorer boiler ratios.
     
  18. pete2hogs

    pete2hogs Member

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    There is no evidence that the 'dean goods' proportions helped a V2 under normal circumstances - although apparently they made a lovely noise. Townend goes into the issue in some detail in a couple of his books. The Kylchap, on the other hand , did make a difference. A big difference.
     
  19. Courier

    Courier New Member

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    Apart from the official report. For another example, J F Clay wrote....

    The engines that were given the Swindon treatment were welcome on the GCR, they burnt more coal but did more work. They were reliable, good running machines that were less selective about fuel...... There was disappointment that the modifications, which were simple and cheap, were not spread more rapidly to other engines in the class. (Essays in Steam)

    The Kylchap may have made a big difference to the performance of the few V2s fitted - but made very little difference to the running of the railway - as by the 1960s it was too late.
     
  20. LMS2968

    LMS2968 Well-Known Member

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    While agreeing that there was a built-in weakness in the A1 / A3 frames, I struggle with the idea that that raising the power output and hence the stresses imposed on them did nothing to increase their failure rate.
     

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