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Driving a compound locomotive

Discussion in 'Steam Traction' started by andrewtoplis, Nov 17, 2021.

  1. bluetrain

    bluetrain Well-Known Member

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    The Fowler 4-cylinder compound pacific proposal of 1926 was designed to an overall width of 8ft 8in to fit the restrictive LMS loading gauge. Cylinder diameters were 16.75in outside HP and 23.625in inside LP. Now if that design had been built, but later given Chapelon type improvements ...........?
     
  2. Eightpot

    Eightpot Well-Known Member Friend

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    BR reckoned that a fireman could shovel 1 - 1/2 tons of coal continuously, and 2 tons for one hour. Chapelon and Colonel Rogers both claimed that Fireman Marty shovelled no less than 4 tonnes per hour on test with the 4-8-0 rebuild No. 4707, and according to Rogers, 'refusing all assistance'. That works out at 1 - 1/3 cwt per minute, and every minute for an hour, besides attending to his other footplate duties. Is this really believable? Or did they have super-human firemen in France?
     
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  3. Jamessquared

    Jamessquared Nat Pres stalwart

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    Is it recorded under what conditions chauffeur Marty achieved that feat? If the intention was simply to test the limits of sustained steaming rate, then having an inspector on the footplate to keep a lookout, attend to the water etc., would no doubt enable the fireman to adopt a "head down, arse up, and shovel like fury" stance, but it is hardly a realistic indication of what could be achieved in the real world. Records may garner publicity, but the real locomotive performance that matters is what you can reliably attain day in, day out.
    Which rather starts to negate the point of high power. Unless you make a saving in crew, two smaller locos will always be operationally more useful than one larger one.

    Tom
     
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  4. 30854

    30854 Resident of Nat Pres

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    Mais oui, d'accord!

    Joshing aside, I recall comment that mechanical stokers were considered an unnecessary luxury in UK locos, as grate areas of over 50ft/sq were comparatively rare. Odd that figure seemed to take more account of the grate size than the firing rate. I'm guessing a Duchess with 14 on over Shap is a rather different proposition to a MN haring through Woking with owt other than one of the Belles which went thataway.

    As Tom pointed out, there's a world of difference between a one-off showpiece and regular operations, but as the discussion seems to be heading into firing rate territory, a question occurs. Had UK loco development necessitated locos much larger than Stanier or Bulleid pacifics, at what point would mechanical stokers have become desireable?
     
  5. 242A1

    242A1 Well-Known Member

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    Marty used to be a stoker on torpedo boats but it is said that he preferred working in the open air hence his appearance on the railways. A one hour test is written of where the speed was maintained at 62 mph during which Marty fired four tons of coal. 4521, later 4707, was tested on 16th August 1932 and it proved capable of delivering a continuous 3,450 ihp and reaching 4,000 ihp, it also reached a speed of 94 mph which was in itself quite an achievement for the time with 6' 3/4" driving wheels. The fireman in this case does not appear to have been recorded.

    You do not need the maximum output all the time, you are not always trying to maintain line speed on an eight mile climb on a 1:125 while hauling 600 tons or maybe more than 800. The French engines in question could dispose of this ascent in under 8 minutes. If you did need more power or needed it to be delivered for longer the 25 engines of the 240P class had mechanical stokers and could deliver 4,400 ihp. Solutions are there to be found, it is a question of looking. You do not need to expect too much of your well trained crew other than on a very occasional basis and neither do you, particularly in the UK, need to consider the use of two engines as a regular expedient.
     
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  6. MellishR

    MellishR Part of the furniture Friend

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    Apropos 10000
    The essence of compounding is that you expand the steam in two (or more) stages, so you don't need short cutoffs; but 90% would mean hardly expanding the steam at all in the HP cylinders. Would that really make sense?
     
  7. 242A1

    242A1 Well-Known Member

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    Chapelon used 80% HP cut off associated with 50% LP cut off in 242A1. Consider the swept volume of the cycle. In 10000 when fitted with 10" bore HP cylinders the volume of the LP cylinders was four times that of the high.
    The equivalent of 20% cut off in a simple expansion engine can be seen as full stroke admission on the HP and zero in the LP. A 40% simple expansion cutoff, again full stroke in HP with the LP being 25%. and so on. Short HP cutoffs are disastrous but it does take a while to get your head around the thinking and we don't have an engine with which to conduct our own tests all we have are the records of trials taking place many years ago and largely elsewhere in conjunction with some work undertaken by some interested individuals who chose to revisit projects which did not quite deliver and then went on to work out why and also try to work out what might, or indeed ought to, have happened.
     
  8. Allegheny

    Allegheny Member

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    Two smaller locomotives would rule out a non-stop run using a corridor tender.
     
  9. bluetrain

    bluetrain Well-Known Member

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    Thanks for the photos. One of the Zillertalbahn engines is on loan to the Welshpool & LLanfair Railway in Wales, but I think it is non-compound. The North-Eastern Railway "Aerolite" engine has survived but has been in a museum since 1934. So our only full-size working 2-cylinder compounds are road traction engines.
     
  10. Hermod

    Hermod Member

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    It is number two that is on loan to W&L.

    https://www.zillertalbahn.at/data.cfm?vpath=technische-details-excel/lok-2

    For people like me that finding two cylinder compound versus simple (Saturated and superheated) is the most important question to day,I would ask for loan of one IoM engine.
    Space enough and not to heavy parts.Has there ever been run some dynamometer tests on IoM?
     
  11. marshall5

    marshall5 Part of the furniture

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    You could always ask but I doubt that you'd get a polite answer. Dynamometer tests??????.... we only started using continuous brakes about 30 yrs ago!
    Ray.
     
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  12. 30854

    30854 Resident of Nat Pres

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    Dynamometer tests? I suspect that'd likely be a "no"!

    Oh, how nice it would've been if just one of the NCC S/S1 compounds had survived. The archive at MOSI certainly contains a BP G.A drawing (and official photo), which would be a good starting point for any would-be newbuild, though a fair bit of computer modelling would seem to be in order.

    F'raid I'm committed to a NLR 4-4-0T and even that's predicated on a thus far elusive lottery win! :(
     
  13. Bikermike

    Bikermike Member

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    Slick Bass has got a good dyno up in Andreas, if it can manage a 200 bhp superbike, it can probably manage a manx tank... balancing on the single roller might be a challenge
     
  14. Hermod

    Hermod Member

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    A dyno thing for railways is just force measuring sensor between loco and load and a speed over ground sensor.Force times speed is power.
     
  15. Bill2

    Bill2 New Member

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    Thinking about Gresley's 10000 I suspect that performance and economy were inhibited by the 6" valves to the high pressure cylinders, and possibly by the size of the ports, steam chests, and passages as well. Steam at 450 psi is a lot less voluminous than at the usual pressures, but the water tube boiler produced 20,000 pounds/hour on test and that is a lot to pass through two 6" valves. For comparison, think of a 2-cylinder simple working at 45o psi: to obtain a tractive effort of between 30,000 and 40,000 pounds requires cylinders of about 16" to 18" diameter which would have valves of 8" or 9" diameter by contemporary standards such as the Castles, Lord Nelsons, or Royal Scots. Even 8" valves have nearly twice the cross-sectional area of 6" valves, even more for 9" valves. The Castles and Lord Nelsons are an interesting mnemonic: steam at 225 psi has very roughly twice the volume of that at 450 psi, and these locomotives had four valves to handle it instead of two. Incidentally the 8" valves for the 20" low pressure cylinders of 10000 also look small.
    In retrospect, it is unfortunate that 10000 was designed and built just a bit too early for the lessons of Chapelon's work to have sunk in, because the success he achieved with PO pacific 3566 was by easing the flow of steam including doubling the size of the steam passages.
     
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  16. 30854

    30854 Resident of Nat Pres

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    The details of the W1 are unfamiliar to me. Were such small piston valve diameters forced on Gresley by considerations of space? Perhaps the loco came too early to draw lessons from Chapelon, certainly not too late to have heard about problems experienced in the steam circuit of Lawson Billinton's B4x rebuilds, some 15 years earlier.
     
  17. Eightpot

    Eightpot Well-Known Member Friend

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    Maybe, but they would appear to be the same cylinders and valves as used on the original A1 Pacifics.
     
  18. 242A1

    242A1 Well-Known Member

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    I agree with you that the valves look to be on the small side and we do not know the area of the port openings either. We can be sure that no short cutoff working (by simple expansion standards) was tried - the shortest HP cutoff used in 1935
    was 30%. As far as the regulator opening was concerned we simply do not know.
    The results of the 1935 trials tell us only so much. One of the tests conducted on 5-6-35 delivered the highest dbhp at 17o2 at a speed of 56.7 mph and with a drawbar pull of 5.02 tons. The cutoffs were 50% in the HP and 55% in the LP and this is where things get a little more interesting. The boiler pressure was 470psi, the HP superheater temp was 735F/390.5C, the receiver 400F/204.4C and the LP superheater temp 610F/321C. The exhaust pressure was 6.00 psi. the smokebox vacuum 9.00" and its temperature 690F/365.6C. The HP steamchest pressure was 390 psi and the LP receiver 102 psi and that HP steamchest pressure raises the question about the regulator because no matter how the engine was being worked there was always a drop. I would like more information but I don't think I will find it.

    3566 appeared in 1929 the same year as 10000 and it gave a glimpse of what might be achieved with compound expansion locomotives. The LNER engine was an experiment to try to match the efforts of a then existing orthodox type with greater efficiency and the selection of a 450 psi working pressure must have been deliberate in this, check variations of Btu/lb with pressure. The engine was a work in progress and few if any understood what the design might be capable of. The results of Chapelon's work were a two edged sword in that they showed and confirmed where large improvements could be made in locomotives and these could be applied to both simple and compound types and the improvements in simple types were enough to persuade people not to continue with compounds. Beginning to understand what 10000 and LMS 6399 might be capable of came about too late.
     
  19. Bill2

    Bill2 New Member

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    Very interesting to see the full figures for 10000 on test which I haven't come across before. As mentioned, pressure in the high pressure chests shows a worryingly large drop from the boiler; as suggested, possibly the regulator was not full open otherwise the cross-section through the superheater would seem to be too small. Pressure in the low pressure receiver also looks low for high pressure cylinders working at 50% cutoff though one doesn't know what to expect for a locomotive working at 450 psi; possibly the cross section through the intermediate superheater was too small as well? The heating surfaces of the superheater were not particularly large in the first instance and it also appears that installation of the reheater reduced not only the heating surface but also the cross section through the main superheater. These pressure drops certainly suggest one reason that 10000 did not achieve the hoped for efficiency.
    The low pressure cylinders and valves of 10000 had the same dimensions as Gresley's A1 but the RCTS book implies that they were not identical, though actual differences are not mentioned except that 10000 could work at 75% cutoff whereas the A1's were limited to 65% to prevent over running of the inside valve. The 8" diameter valves of the A1 were the largest that could be fitted alongside the 20" inside cylinder so larger valves could have been used for 10000, as were in fact incorporated in the A4s somewhat later with smaller cylinders. There seems no reason why the inside valves were so small, though valves 50% of cylinder diameter were typical of the times.
     
  20. Bikermike

    Bikermike Member

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    If you look at the 3d drawings on the P2 page, the steam passages look pretty convoluted on what is presumably a cannonical Gresley front end, so at some point it would become a limiting factor, albeit one enforced by loading gauge at some point.
     

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