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Pennsylvania RR Duplex 4-4-4-4 replica build

Discussion in 'International Heritage Railways/Tramways' started by Martin Perry, Jul 25, 2017.

  1. Martin Perry

    Martin Perry Part of the furniture Staff Member Moderator

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    That overspeeding was almost certainly the result of wheel slip at high speeds.
     
  2. Jon Pegler

    Jon Pegler New Member

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    Quite possibly, but there were some logged runs in late 1946 at 135-142 mph that occurred, without slipping at high speed.
    Most slipping seemed to happen at lower speeds.
    A lot of research went into the metallurgy of the valves after that date, with little results.
    Julius Kirchhof, the head of Franklin's poppet valve development was surprised when cast iron valves performed so well, and exclaimed that 'you can't make valves out of s--t', despite all the other materials used for valve tests.
    Alas, US steam was almost dead by 1946.
     
  3. Martin Perry

    Martin Perry Part of the furniture Staff Member Moderator

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    Those logged runs were, I believe, based on passing times at Switch Towers.
    The T1 had quite a reputation for slipping at high speed.
     
  4. Jon Pegler

    Jon Pegler New Member

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    The slipping problem was really the downfall of the Duplex design.
    Even the Q2 anti slip device did not entirely solve the problems, and would not have had a quick enough reaction at the speeds the T1s were performing at.
    Maybe a modern electronic device will work quicker to stop a slip before it becomes too uncontroleable?
    Ralph Johnson's ideas were fine in theory, but steam in the US had past the point of no return by the time the Duplex was developed.
    It will be interesting if the new build has any answers to any unanswered questions, once it is up and running.
     
  5. Martin Perry

    Martin Perry Part of the furniture Staff Member Moderator

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    I’ve read that some drivers really took to them and could control the slipping, but others were either unaware or didn’t care. As you say, the time had passed anyway.
     
  6. 30854

    30854 Resident of Nat Pres

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    Re: slipping. The project website (https://prrt1steamlocomotivetrust.org/ ) addresses the matter thus:

    "The wheel slip issue had two root causes. The first was ineffective spring equalization. As originally designed (engines 6110 and 6111), the engine truck was not equalized with the drivers, and all four pairs of drivers were equalized together. When entering curves or moving over track that was less than perfectly level, weight was transferred off the front engine, causing the front pairs of drivers to slip. This condition was observed at all speeds, and we believe is the basis for the “uncontrollable” reputation the T1 has. The PRR addressed this in the production fleet by splitting the spring rigging in two – the front engine was equalized with the engine truck, and the rear engine was equalized with the trailing truck. The other root cause was improper handling. Engineers assigned to T1s were given no formal training on how to operate them, and their performance was very different than the K4’s most of them were accustomed to. The front end throttle, high boiler pressure, very large diameter steam delivery pipes, and poppet valves combined to make the T1’s very responsive to throttle application compared to a K4. Too much power applied too quickly resulted in wheel slip, especially at speeds around 15-25 mph. We will be performing kinematic and compliance simulations of the spring rigging and equalization to determine whether further improvements in adhesion are possible. We will be applying a wheel slip alarm, so the engineer would be made aware of a wheel slip more quickly should it occur, and reduce power manually. We will also investigate fitting an electro-mechanical anti-slip device similar in concept to that fitted to the Q2, but with more reliable valves and modern electronics, so no involvement from the engineer would be required."

    The comment about responsiveness to the throttle leading to slipping put me in mind of another, in relation to a comparison between original and rebuilt 'Bulleids', to the effect that the originals responded as soon as the regulator was opened. Perhaps some of our number familiar with both may care to pitch in?
     
    Sheff likes this.

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