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Tank v Tender Locos

Discussion in 'Steam Traction' started by johnofwessex, May 17, 2017.

  1. 8126

    8126 Member

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    Very interesting. If my interpretation of this is correct, an Bulleid West Country comes out as 5P7F. I guess the SR did some judicious modification against known performance there. It penalises wide fireboxes quite severely; a King Arthur actually squeaks into 6P by my reckoning, but I don't think anyone would question which of the two classes was the more powerful passenger loco.

    I can't see how anything can be classified as 8P at all, given the 4480 lb/hr firing rate limit - by the calculations provided a superheated loco can only just make 7P. Maybe 8P was recognition of locos with the capability for feats of high power for as long as the fireman could stand it.

    Firing rate limit: 4480 x 6.18/20 x 0.00335 = 4.64 tons
    Actual Merchant Navy: 48.25 x 30.7 x 0.00335 = 4.96 tons

    Staying vaguely on topic, the L&Y Dreadnought tanks are just below the 5P/6P boundary, limited by their boilers.

    Oh, and the LSWR D15 I cited earlier as hard done by at 3P - yes, it edges into 4P with cylinder tractive effort the limiting factor.
     
  2. Jamessquared

    Jamessquared Resident of Nat Pres

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    Taking big tank engines, if I have calculated right, the Billinton L class 4-6-4T just about squeaks into class 5 (limited by grate area - 26.7 sq ft * 40 * 0.00335 = 3.58tons drawbar pull). BR rated the N15X rebuilds as class 4P.

    Tom
     
  3. Railcar22

    Railcar22 New Member

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    Here is a resume of the big GWR tank engines
    81XX 2-6-2 ttank engines of which 9 built over 31,000lbs tractive effort.
    4200 2-8-0 tank engines 31,450lb Tractive effort 7F
    5205 & 7200 2-8-0 & 2-8-2 tank engines 33,170Lbs tractive effort 8F
     
  4. LesterBrown

    LesterBrown Member

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    It was the five locos of the second 31xx that had 31170lb reactive effort, but they were still only 4MT.
     
    Last edited: May 20, 2017 at 12:07 AM
  5. Jimc

    Jimc Well-Known Member

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    An interesting question is whether 4200s that received new front ends were given 19" cylinders, which would presumably make them 8F in practice. The 4253 group state that their locomotive (new front end in 1947) has 19" cylinders. The usefulness of such distinctions may be mulled over by considering what the actual difference in diameter and thus nominal tractive effort would be between 18.5in cylinders on last rebore and new 19" cylinders. In his book Cook tells us about a Saint that had nominal 18.5" cylinders bored out to more than 19".

    Lester is of course quite right. Presumably they stayed at 4MT because of a "lowest number of" calculation.
    Steve's excellent and much appreciated post doesn't tell us how xMT was arrived at. Was it just that 4P and 4F (or whatever) tended to coincide and 4MT was a shortcut?
     
  6. Jamessquared

    Jamessquared Resident of Nat Pres

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    What's "MT"? Would be e.g. 2P 2F where I come from ;) (And another letter for braking capacity, but that's a different story...)

    Tom
     
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  7. MellishR

    MellishR Well-Known Member Friend

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    Any chance of making that available in a format other than JPG, which makes the wording unclear when magnified?
     
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  8. LesterBrown

    LesterBrown Member

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    I doubt Swindon spent much time over it and wanted to keep the extra lettering as brief as possible; as far as they were concerned they'd be power class D, E etc. anyway.
     
  9. 8126

    8126 Member

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    The chart seems to indicate that MT and P classifications were essentially arrived at in the same way, see the drawbar pull calculation being given for "Passenger and mixed traffic engines." Certainly, if you have a boiler limited passenger class it's likely to have an equal or higher freight classification.

    However, if you follow the chart to the letter, nothing with a GWR No.2 or No.4 boiler gets more than 3P or 3MT anyway, so I doubt Swindon were following it too closely. Of course, they weren't the only ones; a Southern U is apparently 4P6F if you follow the chart, as opposed to 4P3F as actually classified.
     
  10. Tim Light

    Tim Light Active Member

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    Makes you wonder whether any practical use was ever made of these classifications. I'm sure that most shedmasters would know which types were best suited for each assignment without reference to the power class.
     
  11. Jimc

    Jimc Well-Known Member

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    Its well established that the Western region continued to use the GWR classification. I'm sure that shedmasters knew very well what of their local fleet was best suited to which turns, but when they had a foreigner on their hands I imagine the classification was useful.
     
  12. flaman

    flaman Well-Known Member

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    I wonder whether much weight was given to official power classification or even technical suitability. I'm sure it was more a question of making the best use of whatever was available.

    The two lines which I was most familiar with in steam days were the ex GE Southend Victoria line and the former London, Tilbury & Southend Railway. Both ran from the City of London to Southend, or a little beyond in the LT&SR's case, carrying similar traffic through similar country; yet the LT&S was an almost exclusively tank engine line, whilst the Victoria line was worked almost exclusively by tender locos. I suspect that this was due to historical circumstances; when the LT&S became independent of the GER it adopted a type of 4-4-2Ts which, with some upgrading, served very well until the 1930s, when the LMS introduced, as part of a modernisation scheme, the 3-cylinder "2500" class 2-6-4Ts, built specifically for the line. These were augmented after WW2 by some Fairbairn and BR Standard 2-6-4s, which worked passenger services until electrification in 1962.

    Things were quite different on the ex GE line. Stratford M.P. district were never short of former express engines which were cascaded down to run the fairly tightly timed Southend services in hot competition with the rival system. Thus in my recollection almost all Liverpool St.- Southend Vic. services were hauled by a random mixture of B12, B17, B2 and B1 4-6-0s. L1 2-6-4s appeared from time to time but not regularly, they seemed to be mainly restricted to the shorter suburban routes.
     

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