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Technical questions, Hammer Blow.

Discussion in 'Locomotive Engineering M.I.C' started by Ploughman, Jan 16, 2014.

  1. Ploughman

    Ploughman Part of the furniture

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    Thought I would start a thread that tried to find answers to those questions that bug you.

    Hammerblow
    I think most people have heard of this.
    But What is it?
    What does it affect and how?
    What speed does it start to be a factor in damage considerations?
     
  2. The Saggin' Dragon

    The Saggin' Dragon Nat Pres stalwart Staff Member Moderator Friend

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  3. b.oldford

    b.oldford Member

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    Wouldn't the MIC section be far more appropriate for a thread of this nature?
     
  4. Big Al

    Big Al Resident of Nat Pres Staff Member Moderator Friend

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    There's not much to add to the Wiki description but the consequences of this not now being a regular feature on the rail network are considerable. It's probably best seen in the differentiated speed limit signs by the lineside where units and loco (diesel or steam) hauled are subject to different maxima. Although this relates primarily to the (axle) weight of what is passing, possible hammer blow effects are still a factor. It is sad that track and other infrastructure maintenance has "levelled down" to the type of traction using it. But as has been said many times before, steam is a guest on the network and in the same way that the overall "envelope" of locos can limit their free movement because they are out of gauge, their weight and the hammer blow effect can also limit their speed. The characters RA9 are not a particularly helpful route availability to have badged on the cabside nowadays.
     
  5. Steve

    Steve Resident of Nat Pres Friend

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    When the 9F's were doing their high speed exploits in the 1950's, someone worked out that, at 90 mph, there was enough out of balance force to momentarily lift the wheels off the track each revolution. This has the opposite consequence of the loco being dropped onto the track every wheel revolution - about 6 times per second. Not very good for bridges! It may be an extreme but gives an idea of the forces involved.
     
  6. The Crimson Pirate

    The Crimson Pirate Member

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    Paper 432 by E. S. Cox in the Journal of the Institute of Loco Engineers provides some useful information.
     
  7. Ploughman

    Ploughman Part of the furniture

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    Thanks for the replies.
    However one question still to answer.
    Is Hammerblow a factor to be considered in PW design on preserved lines running at 25 mph?
     
  8. The Saggin' Dragon

    The Saggin' Dragon Nat Pres stalwart Staff Member Moderator Friend

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    I don't think that there is a lot of 'design' work on preserved lines PW, outwith P&C at least.
     
  9. Steve

    Steve Resident of Nat Pres Friend

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    In terms of PW, I'd say no, whatever the speed. In terms of underlying structures, the answer is probably yes. A loco can just happen to slip on a bridge and do a lot more than 25mph in terms of RPM.
     
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  10. Ploughman

    Ploughman Part of the furniture

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    So all relay work on preserved lines currently is being done without a design in place?
    Curve radius, Clearances and Gradients are being ignored?
    I think not.

    Current relay work on the Bluebell shows the use of Laser Dozers in use blading the ballast. These machines require a gradient from a Track Design scheme.
     
  11. The Saggin' Dragon

    The Saggin' Dragon Nat Pres stalwart Staff Member Moderator Friend

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    I doubt that much of it is committed to paper or autocad to be honest. I would imagine that much of it is done by experience/rule of thumb etc. maybe things have changed since I was involved.
     
  12. Jack Enright

    Jack Enright New Member

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    I'm not sure what P & C is, but I'd have thought there was plenty of design work involved where major work is undertaken (such as the demolition of the old embankment at the bottom of Tenterden Bank and its replacement with a completely new one, with a very different construction), and where lines are extended over old trackbeds which have been abandoned for years - or where significant deviations are undertaken, such as the narrow gauge Welsh line whose original trackbed was covered by a new reservoir. Equally, the K & ESR extension west of Bodiam had to have a deviation over fresh ground, as the original trackbed at one point is now the drive-way of a private house. Another case was on the Peak Railway, laying out the new track going into Matlock Station - I doubt the inspecting officer would have been impressed if told that "we just went by experience and rule of thumb".

    Even more so when lines are re-built which were lifted as far back as the closure of the Lynton & Barnstaple - and where you might need to rebuild bridges and re-align heights and clearances to allow for modern road traffic.
     

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