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Current and Proposed New-Builds

Discussion in 'Steam Traction' started by aron33, Aug 15, 2017.

  1. 2392

    2392 Well-Known Member

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    So here goes for another off the wall none steam suggestion for a "new build". Linking in with Steve Middleton and the North Eastern petrol Electric railcar and the G.W.S. steam railmotor. How about a new build Armstrong Whitworth diesel Railcar of the same type as the Trio; Tyneside Venturer, Northumbrian and Lady Hamilton. Yes there was a fourth but it was a "light weight" slightly different railcar. The trio were up to a point quite successful as the L.N.E.R. took them into their ownership, unfortunately WW 2 did for them, what with being a very small none standard class. As for a name for this 4th railcar and being slightly Freudian how about Lord Collingwood. He being an Northumbrian and Lady Hamilton being his good friend Horatio Nelsons' mistress.......:rolleyes:
     
    Last edited: Mar 18, 2018
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  2. Steve

    Steve Resident of Nat Pres Friend

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    Water is weight and you are generally needing to keep this to a minimum, even though it provides a reserve of energy with a steam boiler. So, why a taper boiler? Well, you have a firebox with its associated tubeplate but there is a significant water space around that firebox. The tubeplate size determines how many tubes can be fitted. If the boiler barrel is parallel, then the smokebox tubeplate has an area around the tube nest that is not used for tubes so it makes sense to reduce the size of the smokebox tubeplate to the minimum required to accommodate the tubes and doing this results in a taper boiler barrel. You could have a fancy throatplate which narrows down to a parallel barrel but that is a complex pressing. Modern Belpaire fireboxes are tapered in plan, being narrowest at the backplate and widest at the throatplate, primarily to save water/weight but also to provide increased flexibility through longer stays in the breaking zones. Hopefully, this picture will help with the explanation.

    Churchward boiler.jpg
     
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  3. Kylchap

    Kylchap Member

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    Very clear explanation. Thanks.
     
  4. 30854

    30854 Resident of Nat Pres

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    Thanks for the explanation. In the case of taper atop the boiler, the weight saving, compared with parallel construction, would surely be less marked, given that we're then largely talking about the geometry affecting the volume of the steam space above the water level(?).

    The point I was attempting to get my head around concerned the volume of water contained within the lowest part of the fullest diameter within the boiler in Bulleid's design (i.e. immediately forward of the throat plate) which, but for the thermic syphons, would have been a bit of a 'dead spot', circulation wise. Did anyone other than OVSB utilise an underslung taper?

    In this broadside view of sectioned 35029 (courtesy reddit.com), the taper seems less pronounced than on most other locos, though perhaps that's merely a trick of perspective - or just my lousy eyesight(!):
    35029-ellerman-lines.jpg.cf.jpg

    ..... then, of course, there's Mr Spooner's 'wagon-top' layout. Which AIUI, has more to do with the inherent strength of a double-length boiler barrel than owt else, though I'd expect it's also pretty useful in avoiding priming.
     
  5. Steve

    Steve Resident of Nat Pres Friend

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    Boiler tapers can be a bit misleading when wrapped up in cladding sheets. It is usual to only taper the first ring of the barrel, adjacent to the firebox, which can be quite short, especially on a three ring barrel, as with 35029. However, when the cladding is fitted, it is usual to taper the cladding for the full length of the barrel, rather than accurately follow its profile. Not 100% certain but I think this is done for aesthetics, more than anything else.
     
  6. Jamessquared

    Jamessquared Nat Pres stalwart

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    If you look st a Maunsell S15, the taper is in the front ring, behind the smoke box. It’s quite subtle though - only a matter of about four inches change in diameter, from memory - and easy to miss if you aren’t looking carefully. Lots of people assume they have parallel boilers.

    Tom
     
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  7. Martin Perry

    Martin Perry Nat Pres stalwart Staff Member Moderator Friend

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    Did the cladding follow the taper? (Its a long time since I looked at one)
     
  8. Jamessquared

    Jamessquared Nat Pres stalwart

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    Yes. But you need a really good view to notice - I’ve just spent a bit of time googling for images and it’s hard to find a really conclusive picture.

    Tom
     
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  9. 30854

    30854 Resident of Nat Pres

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    The 'aesthetics thing' works the same the other way round too. The GSR '800's' were, despite appearances, parallel boilered .... as are Greenley's (superb) pacifics on the RH&D.

    In the case of Irish practice generally, tapered boilers remained rare. I believe construction and maintenance costs of tapered boilers was judged too high by the GS&W and MGWR (no other grouping constituent had particularly large locos) to be worth widepread adoption and a lot of reports on comparative practices were produced both at grouping in 1925 and in the aftermath of formation of the CIÉ in 1945). In view of the often extremely constrained axle load limits across much of the Irish network, this has always puzzled me a bit, though the late survival of so many 19th century locos until the final demise of steam (along with many branch lines) may have more than a bit to do with that. I do know that a frequent criticism of "English" loading gauge locos revolved around a boiler's steam production capacity (and the paucity of space in cabs!), though I've always suspected this was more imagined than real.

    Not even Bulleid produced any tapered boilers for the CIÉ ..... his only one example being square!

    I'm still racking my brains as to whether there's any reason, other than thermic syphons, which would cause a designer to adopt an underslung taper.
     
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  10. Martin Perry

    Martin Perry Nat Pres stalwart Staff Member Moderator Friend

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    And did the H15s have the same boiler? They definitely look parallel (on the outside at least!).
     
  11. Allegheny

    Allegheny Member

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    To make space for the cylinders?

    For many years I thought that the boiler tubes "splayed out" to follow the lines of the taper, to improve water circulation at the firebox end. The tubeplate could be slightly curved if required to be perpendicular to the tubes.

    I now know this is incorrect, but would it make any difference?
     
  12. Steve

    Steve Resident of Nat Pres Friend

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    Didn't you essentially answer your own question in post 1864? Having the taper at the top largely reduces the volume of steam carried and hence not much weight, compared with having the taper at the bottom, which largely affects water space and, thus, weight. It does have the aesthetic disadvantage that the top of the smokebox is effectively higher, necessitating a short chimney to keep within the loading gauge. It always amazes me that boiler designers managed to produce such good boilers, given the constraints imposed by the loading gauge, frame width, wheel diameter, wheelbase, axles and, not least, the ability to see out of the front windows
     
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  13. 30854

    30854 Resident of Nat Pres

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    Didn't want to be considered presumptuous in the (all too possible) case I hadn't quite got my head around it all! Given there's been no confirmation (or otherwise) of my own suspicions about underslung tapers only being really useful where syphons are fitted, I'll defend my caution for the time being.
    That's an interesting notion. Though you probably don't want to read too much into it, I'm certainly not aware that any vertical clearance won by a taper has been used like that. Given some of the problems caused by tortuous and constricted steam passages down the years (Lawson Billinton's B4x springs to mind), perhaps you've spotted a trick designers overlooked.

    Wonder if we've any design specialists (or SM&EE types) who could comment?
     
  14. 30854

    30854 Resident of Nat Pres

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    Which flavour? Original or Swindonised? I know which I'd find the more appealing of the two options, plus the rebuilt version - even though it looks the more practical of the two - doesn't seem a million miles away from the sort of thing the GWS folks might get round to building eventually (thinking "Barnum").
     
  15. Mr Valentine

    Mr Valentine Member

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    Well now, if the cladding awards are in full swing, my shout goes to 1442 in Tiverton, with it's tapered middle section expertly crafted onto a completely parallel barrel, no-doubt the work of some Swindon chancer many moons ago.

    As for GWR 2-4-0's, may I humbly suggest an inspection of the P class boiler currently sat to the rear of Didcot locomotive works, followed by a trip to York to look for any Stella or 3232 drawings, before finally finishing off the whole exercise with a helpful dose of reality check, lest blinding by roses-tintedness set in.
     
    Last edited: Mar 12, 2018
  16. Jamessquared

    Jamessquared Nat Pres stalwart

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    Complex as always. But in outline the original Urie series had parallel boilers. 335 (the Urie rebuild of a Drummond E14) also had a parallel boiler, but with slightly different proportions to the others. The Maunsell H15s had the coned boiler shared with the N15s and S15s. 330 - 334 (the Maunsell rebuilds of Drummond 4-6-0s) had parallel boilers similar to 335. (I think they preserved the barrel the Drummond originals but with new fireboxes). After 1927, No. 491 (of the Urie series) gained a new coned N15 boiler; the original parallel boiler from 491 was repaired and became a spare for the Urie series locos.

    Tom
     
  17. Jamessquared

    Jamessquared Nat Pres stalwart

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    I suspect tapering the bottom of the barrel helps with space for the middle cylinder.

    Here's an outline drawing:

    [​IMG]

    The smokebox (such as it was on an original loco) diameter is smaller than boiler barrel diameter to squeeze above the cylinder. If the boiler was straight (rather than tapered) along the bottom, that situation would be even worse. So it looks to me like the boiler needs to be tapered to save weight, and putting the taper on the bottom (rather than the top) helps provide a small, but valuable, extra bit of clearance for the middle cylinder.

    Tom
     
    Last edited: Mar 12, 2018
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  18. 30854

    30854 Resident of Nat Pres

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    Seems logical, but thus far at least, still no non-Bulleid examples of underslung tapers.

    I wonder how the 2cyl vs 3cyl arguments stack up in reality, With Thompson and Riddles (probably Ivatt fils too) as convinced 2 outside cyls were the way to go as were Raven, Gresley and Bulleid, who's view was that upping the grunt whist being kind to PW justified the extra hassle.
     
  19. Martin Perry

    Martin Perry Nat Pres stalwart Staff Member Moderator Friend

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    Thanks ... complex indeed :)
     
  20. 30854

    30854 Resident of Nat Pres

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    It's certainly an 'interesting' take on the notion of standardisation.
     
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