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Sir Nigel Gresley - The L.N.E.R.’s First C.M.E.

Discussion in 'Steam Traction' started by S.A.C. Martin, Dec 3, 2021.

  1. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    I will get pilloried for this, but I have read that too and there's an element in my view of Holcroft playing a bit fast and loose with that. Nobody disagrees that the two men were trying to achieve the same thing, but Gresley's gear is definitely different to Holcroft's gear. Tom's photographs above show a very different setup which - though you appreciate my LNER bias - seems more complicated than Gresley's approach.

    The question of the patent expiring is bit of a red herring. Holcroft let it expire in 1913, Gresley applied for his two years later. Gresley in his patent mentions, without naming, other valve gear types that are designed to achieve the same thing and much of his patent explains how his is different.
     
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  2. 30567

    30567 Part of the furniture Friend

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  3. Spamcan81

    Spamcan81 Nat Pres stalwart

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    The form of derived motion on 461, the O2 prototype, was quite different to that fitted to the rest of the class and his other three cylinder classes. I cant find a picture of it at present but from memory it looked quite similar to Holcroft's mechanism.
     
  4. Jamessquared

    Jamessquared Nat Pres stalwart

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    As @30567 says, there was relatively little difference found - certainly insufficient to warrant either rebuilding the sole 90° example (which would have been expensive, needing at a minimum a new crank axle), nor of converting the other members to 90°.

    (There was also I think another example built with 6'3" wheels to trial against the standard 6'9", again with relatively little practical difference).

    Tom
     
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  5. Jimc

    Jimc Part of the furniture

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    Holcroft's design for the SR was not his original, and Gresley's implementation on the first O2 was not his original concept either. I submit its a mistake to confuse the first implementation with the original concept.

    Holcroft goes through his thinking a bit. He started by drawing a lever between two outside valve rods at 120 degrees phase to each other and tracing the movement of the centre point. This turned out to be 60 degrees out of phase and half valve travel. Given that knowledge it was (to him anyway) obvious to add rocking levers to produce both 120 degree phase and full valve travel. He also worked out a means for it to work with outside cylinders at 90 degrees phase as was found on some 3 cylinder compounds. Anyway the key to the whole thing is the phase relationships and the 2:1 lever(s) to get the right phase and valve travel. So that's Holcroft's original, which was effective for a valve on the centreline. In his book there's a sketch of it drawn up for Maunsell in 1917 on a 4-4-0 with valves above the cylinders and the gear behind the cylinders. There's a 2:1 lever each side, and a symmetrical lever on the valve rod with links between them.

    We're told that Gresley was working on his design for some time and in the later stage had sight of the Holcroft and Joy patents, but his design, although using the same fundamental principles, was significantly different in detail from Holcroft's original and in concept simpler with fewer pin joints and the valve off the centreline. Now we are at the point where Gresley has produced his original O2 design, which has a complicated arrangement of rockers to deal with the valves being on different planes. So at this point we can say there are Holcroft designs and Gresley designs for conjugated gear.

    What comes next apparently partly played out in the letters page of "The Engineer", and if anyone has a subscription to "Graces Guide" perhaps they could confirm. According to Holcroft Gresley described and illustrated the O2 and the implementation with extra rockers in an article in the magazine, and it came in for criticism. Holcroft, however, wrote a letter where he demonstrated that all three valves could be put in the same plane by adjusting the crank angle so the valve timing was correct. So this was the Holcroft-Gresley gear, Gresley's original design modified for a simple implementation with an inclined middle cylinder.

    Then after that we have Holcroft's design for the N1. This was a fourth implementation, and was really a development of the Holcroft-Gresley gear, not Holcroft's original design. Is anyone not confused yet? In this one the Holcroft/Gresley arrangement is modified so that the drive to the conjugation levers comes from behind the cylinders, not in front of them. Perhaps this should be regarded as Holcroft-Gresley-Holcroft gear, or is that a firm of lawyers?
     
  6. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    It's not - it had rocking shafts for the inside gear, more steeply inclined outside cylinders, but was otherwise the Gresley gear.

    [​IMG]
    [​IMG][​IMG] upload_2023-1-7_13-44-32.png

    Source: http://www.ipernity.com/doc/philsutters/25553491

    But, as I have stated earlier Jim, Gresley's patent of 1916 already has more or less the final version he adopted as one of the options, which you can see in the diagrams and by way of reading the accompanying text and thinking Gresley outlined in his patent. Happy to send you a copy, as I say.

    [​IMG]
     
  7. Spamcan81

    Spamcan81 Nat Pres stalwart

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    The camera doesn't lie but I'm sure I've seen a picture of 461 with motion quite different to that depicted.
     
  8. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    Never rebuilt - stayed the same to withdrawal in the late forties.
     
  9. MellishR

    MellishR Resident of Nat Pres Friend

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    I don't know whether the sentence that I have highlighted accurately reflects what Holcroft was arguing, but anyway it seems to me to mix up two separate issues. Any of these conjugated gears produces valve events for the middle cylinder equally spaced at 120º from the outside valves. If the middle cylinder is inclined differently from the outside cylinders, its associated crank needs to be offset from the equal 120º spacing from the outside cranks. That remains so regardless of whether the valves are in a single plane or not. If the valves are not in a single plane, you may need to do something in addition to couple the drive from the conjugation levers to the valve spindle.

    Or am I up the pole?
     
  10. RLinkinS

    RLinkinS Member

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    In addition to those variations one of the locos had a longer boiler barrel and Lord Howe was fitted a larger round top boiler for several years

    Sent from my SM-A105FN using Tapatalk
     
  11. RLinkinS

    RLinkinS Member

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    The mental process Holcroft went through to design the conjugated gear that operated the inside valves on 4 cylinder 8 beat engines must have been impressive.

    Sent from my SM-A105FN using Tapatalk
     
  12. huochemi

    huochemi Part of the furniture

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    The attached page is from Gresley's 1925 paper to the ILocoE on 3 cylinder Locos. Perhaps not surprisingly, Gresley claimed them to be better at starting, although he uses a max cut-off of 75%. Holcroft in his 1918 paper on three cylinder locos said much the same thing (Holcroft's paper also describes and has diagrams for Gresley's and his conjugation ideas up to that time).
     

    Attached Files:

  13. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    Sorry in advance if this comment comes across as a lightweight contribution compared with the engineering detail by others.

    What strikes me as significant about SNG is his willingness to embrace and understand the thinking of other engineers of the time when it could be argued that his own expertise alone might have been sufficient. To my mind that openness is the hallmark of great engineers.

    Up thread Chapelon was mentioned and we know that these two were in regular contact. Chapelon was also held in high regard by SNG. Yet Chapelon designed the 241Ps that were powerful but arguably too powerful for their lightweight and overly flexible frames resulting in problems with stays and the odd hot box. But that didn't affect the exchange of ideas and of course, that also informed the thinking of each.

    There is a danger if you unpick in fine detail any loco engineer's work that you can forget how developmental it was at the time.
     
  14. Jimc

    Jimc Part of the furniture

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    Thanks. That's roughly what I expect - that the minimum tractive effort at wheel rim is always greater than the two cylinder, and the maximum always less. I just have trouble reconciling that with the statement about starting. But could it be its not the minimum in the cycle that's critical, but the maximum?

    On the other topic, does anyone have access to Gresley's 1918 paper showing the valve gear used on the O2 prototype? It would be interesting to see that.
     
  15. huochemi

    huochemi Part of the furniture

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    Holcroft's 1918 paper has such a diagram. What is the title of Gresley's paper? There is also a diagram in a contemporary Locomotive Magazine. I can let you have copies of these.
     
  16. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    Do you have the full paper, out of interest?

    Really interesting reading, thank you for posting it here.
     
  17. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    If it would be okay, I too would like copies. More reading always good! I am unsure if I have these already so will be interesting to go back through the notes.
     
  18. huochemi

    huochemi Part of the furniture

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    Sure (but not tonight).
     
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  19. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    Most kind, thank you.
     
  20. Steve

    Steve Resident of Nat Pres Friend

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    When we first started discussing this, I did say back in post 961 that I'd redo a starting torque diagram for a 2 cyl loco and an equivalent 3 cylinder loco. This I've now done and it looks like I've got to eat a large slice of humble pie. I've always believed that 3 cylinder locos were poorer starting than 2 cylinder ones and personal experience tells me this. It was explained to me by an ex LNER footplateman as being because, if one piston was at the end of its stroke, the second piston was beyond the point of cut-off (75%) so didn't get any steam. This left just the third cylinder getting steam but, at the 60° position, was still short of being at the point of maximum torque. All this is true. However, in comparing 2 cylinder and 3 cylinder locos at starting, it ignores the fact that, with a 2 cylinder loco, when one cylinder reaches the 75% cut off point, the other cylinder crank is only at the 30° position so not applying maximum torque to the crankpin by quite a way. Thus, although the peak starting torque of a 2 cylinder loco is greater than an equivalent 3 cylinder loco, the minimum starting torque is less than a 3 cylinder loco.
    This doesn't explain my perception that starting a 3 cylinder loco from rest can be more of a problem than 2 cylinder one. I've driven an A1, A2, A4 (two) , V2, Q7, Schools, WC/BB (several) and 71000 so it's a reasonable range of experience of three cylinders. Perhaps I've just been unlucky.
     
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