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Draughting arrangements for Bulleid Pacifics including the Giesl ejector

Discussion in 'Steam Traction' started by jamesd, Oct 14, 2014.

  1. Monkey Magic

    Monkey Magic Part of the furniture

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    Why?

    If there is a known issue that can be improved why would you not take steps to improve it? Especially if it improves performance, efficiency and maintenance? Most locos changed and evolved during their own first working lifetimes to adjust to needs and demands of the day, so it is just a continuation of previous practice.

    I can't help but think that Bulleid would be spinning in his grave at the thought of people not embracing innovative ideas to improve performance.
     
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  2. Steve

    Steve Resident of Nat Pres Friend

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    In which case it would be nonsense to ‘unrebuild’ 35011 because its rebuild was to improve performance efficiency and maintenance.
     
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  3. 30854

    30854 Resident of Nat Pres

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    I get your argument, but effectively curing the drifting exhaust problems common to so many large boilered locos could properly called a safety issue. Doing so with no negative impact on performance is merely a bonus.

    Was that at all convincing? :Angelic:
     
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  4. Monkey Magic

    Monkey Magic Part of the furniture

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    No it isn't. Your argument makes no sense. There is a marked difference between a relatively small change ie drafting improvements and the Jarvis rebuild. Returning it to its pre Jarvis rebuild form does not mean fossilizing it.

    If they were rebuilding it with a completely different valve gear, boiler, firebox, cylinders then I could understand your point but they aren't.

    It is entirely logical to attempt to evolve the prerebuild design.

    Unless you take it back to its as built form it will always be rebuilt and modified.

    Where is the line 7th May 59? March 56? Feb 55? Jan 54? Dec 44?
     
    Last edited: Apr 2, 2021
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  5. class8mikado

    class8mikado Part of the furniture

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    I note with interest the Schools on the NYMR is having its Lemaitre put back on, hopefully they are n,t daft enough just to put the 'SR' version on...
     
  6. torgormaig

    torgormaig Part of the furniture Friend

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    Gotcha!:)

    Peter
     
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  7. Steve

    Steve Resident of Nat Pres Friend

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    No, just the plywood version.
     
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  8. 35B

    35B Nat Pres stalwart

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    Agree completely. If we’re in the realms of “might have been”, then we can reasonably assume that tweaks to the unrebuilt Light Pacifics would have been made to their larger cousins had any been left in original form. But, for this project, the constraint should be to consider what BR might have done 60 years ago, not what a modern engineer might now do given an unrebuilt MN.

    * NB - I’m deliberately using “unrebuilt” to avoid getting drawn into the devilish detail of what constitutes “original” given the in service modifications made to the class.


    Sent from my iPad using Tapatalk
     
  9. Sheff

    Sheff Resident of Nat Pres

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    Steve, sorry to drag the discussion back to this this post, (and further apologises if this has already been addressed, but if so I couldn't spot it reading through the thread), but I don't understand why you would model a Lempor that wasn't designed to the known optimal parameters? Anything else isn't a Lempor is it? Why does it need to have the same outer diameter (of the chimney?) I'm sure there must have been a sound reason?
     
  10. Jamessquared

    Jamessquared Nat Pres stalwart

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    What I don't get in this discussion is why concentrate on the draughting? Of all the criticisms you could lay at the door of a Bulleid pacific, surely the one thing that was never in doubt was their ability to produce steam when needed?

    Tom
     
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  11. JJG Koopmans

    JJG Koopmans Member

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    Yes, and it does not matter what it does cost???
    Kind regards
    Jos
     
  12. Allegheny

    Allegheny Member

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    I would recommend re-reading this thread, starting from about page 2.
     
  13. Jamessquared

    Jamessquared Nat Pres stalwart

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    The answer I would give is that any project has only a limited amount of engineering capacity, so it is important to consider where you expend that capacity. In the context of 35011, the loco requires a new inside cylinder to be designed and fitted (no small task - has anyone in preservation ever replaced the inside cylinder of a Bulleid pacific yet?); a new crank axle to be designed and manufactured; new valve gear and reverser, plus myriad small components. No doubt drawings exist for some of those components, but that is still a huge amount of engineering, design and project management work to be done, not to mention what is likely a seven figure sum to pay for it all. All of those things are on the critical path to success - no middle cylinder, no loco. By contrast, worrying about the draughting of a type of loco that was a prodigious steam raiser feels like displacement activity to me - it might be intellectually satisfying, but it won't be the making of the project. It might break it if it results in too much diversion of limited engineering capacity from items that are absolutely essential.

    Tom
     
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  14. JJG Koopmans

    JJG Koopmans Member

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    All that effort to produce an expensive scarce coal devourer?
    Kind regards
    Jos
     
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  15. Jimc

    Jimc Part of the furniture

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    One might also add to Tom's answer that it would be as well to consider improvements for the various serious design and engineering flaws that caused the rebuilds to be necessary before expending serious effort on an aspect of the design that was merely sub-optimal.

    That being said, though, volunteer resource is rarely a zero sum game. If there is volunteer resource willing to look at the draughting that would not be able to assist with more important items on the critical path then why not?
     
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  16. Allegheny

    Allegheny Member

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    No one would doubt that the Merchant Navy couldn't produce the required quantity of steam. The whole point is that the blastpipe back pressure was considerably higher than it needed to be.

    Correcting this would reduce coal and water consumption and/or generate additional revenue by pulling more coaches.
     
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  17. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    Well said. This is all good discussion but rather pointless unless you are interested primarily in a better view from the footplate that you definitely get with a rebuilt. I will rely on hard evidence from experienced railway men and in that context I would prefer the words of legendary Nine Elms Top Link driver Bert Hooker. He is on record as saying:

    A Merchant Navy’s power outputs were only limited by the fireman’s capacity for work and this was later borne out with the satisfactory trials at Rugby. I don’t think they reached the limit of the boiler there, only the ‘front end’ to use the steam so quickly generated. There is no doubt in my mind that if the best engines from the other regions were put on test against a Merchant Navy, all with clean boilers and steaming freely, but with the tenders loaded up with very inferior coal, the Merchant Navy would still be going long after the others had stalled through lack of steam. A tribute to a really good boiler.

    Nothing more need be said, arguably.
     
  18. Jamessquared

    Jamessquared Nat Pres stalwart

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    But by how much over a complete duty cycle?

    Take a typical mainline trip - a day or so gradually bringing the loco into steam; then an FTR, then a pathing move that will likely have a flyweight load of just a single support vehicle; then the day itself - perhaps a few hours each way with a break in the middle - then another pathing move with the support vehicle, then a controlled cool down. For the vast majority of that cycle, the loco is working at zero or very low output. I get the sense that lots of the supposed benefits of improved draughting are based around assuming a BR-era duty cycle with high availability. Modern conditions aren't like that - the total time spent at high output is small relative to the total period in steam.

    (More carriages by the way - is that actually feasible on today's routes? An original condition Merchant Navy would take 13 or 14 Pullmans unaided up Honiton Bank - about 7 miles of 1 in 75. That's a good 500 tons - convert that to Mark 1s / Mark 2s and you might be talking 15 or 16 carriages, but how many routes could take a train that big? Most stations aren't big enough for trains of that size. So I get the feeling "pull more carriages" is a red herring for a class 8 loco - maybe useful if you turn a class 5 from nine to ten carriages, but not much point allowing a class 8 to go from fifteen to sixteen when it is likely limited by station capacity to about twelve or thirteen anyway).

    Tom
     
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  19. Jamessquared

    Jamessquared Nat Pres stalwart

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    They are all coal devourers though. A typical mainline charter might generate gross income of well over £50,000; and a tender of coal might cost less than £2000 of that. If you save even 10% (and I doubt you would) that's what - a £200 saving on a £50,000 trip? You'd get more bang for your buck negotiating a better deal with your vintner ...

    Tom
     
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  20. Allegheny

    Allegheny Member

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    That's one point I hadn't thought about. Improving the draughting would also reduce the effort required by the fireman.
     
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