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Locomotive Performance and Tractive Effort Discussion

Discussion in 'Steam Traction' started by MellishR, Nov 26, 2022.

  1. class8mikado

    class8mikado Part of the furniture

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    To my knowledge the Kylchap exhaust dimensions of Tornado are as per the Drawings/ measurements of that on Blue Peter and likely identical to those of an A4, A3 Et al.
    It is therefore highly likely that they will be the same on the P2 , falling under the 'if it aint broke dont fix it ' area. If these dimensions are a little ' Tight' for the increased Cylinder volumes and rapid port openings expected with poppet valve gear then at least the worry about drifting smoke is put to bed and the Chuff will be reasurringly beefy. Unless the loco. mysteriously underperforms I don't think this will be looked at.
     
  2. Jimc

    Jimc Part of the furniture

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    Isn't 'to my knowledge' a wonderfully flexible phrase! It can mean just about everything from "I know this 'cos I designed it' to 'I haven't actually heard any rumours to the contrary'!
     
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  3. class8mikado

    class8mikado Part of the furniture

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    In my case its ' in all those chats lectures and books it never said anything about this, and i can remember them better than what i had for breakfast this morning...'
     
  4. Allegheny

    Allegheny Member

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    Does anyone know what the thinking is behind the design of the Kylchap?
    My guess is that the cowls just reduce the turbulence and chaos in the smokebox, but it's just a guess.
     
  5. 30854

    30854 Resident of Nat Pres

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    Sounds reasonable. I've lost count of the number of times I've read of alterations to blast pipe diameter or adjustments to the petticoat, to improve a loco's steaming, seemingly on a fairly hit-and-miss basis. Going right back to Rocket, what are exhaust gases expected to do? What considerations are in play in optimising that function?

    ..... and while we're about it, you can add the Lempor to the list of exhaust systems I've barely got the slightest grip on!
     
  6. Allegheny

    Allegheny Member

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    Just thinking that if this discussion is going to kick off, it might be better on this thread
    Locomotive Front End Designs | National Preservation (national-preservation.com)
     
  7. 30854

    30854 Resident of Nat Pres

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    Doesn't sound unreasonable. Perhaps the whole technical side needs it's own entire section? There's more than a small amount in 'Mutual Improvement', there's been much on fireboxes and grates and oodles on valve gears. Thoughts?
     
  8. class8mikado

    class8mikado Part of the furniture

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    The features seem to be two fold, the Kylala spreader is simply a splitter that divides the blast, like Nozzles in a Lemaitre or Lempor., the purpose of this is to create 4 'virtual' smaller chimneys instead of one big one ( because on larger steam locomotives the optimal length of chimney cannot be accommodated in a single chimney. Lowering the spreader to the blast cap and introducing the stack of Petticoats seems to have been Chapeleons contribution. Porta simplified this into the mixing chamber/ diffuser assembly ( a straight section and a flared section), the purpose of which, for both, is to ( if i understand correctly) to create acceleration, and thus vacuum by creating zones of compression/expansion. Chapeleon may also have wanted the system to draw more evenly across the tube plate... ?

    If the P2 uses your Standard LNER one size fits all double Kylchap i am sure it will work OK, better than a straight single or double chimney. Checking to see if a better ' Fit' is possible is rocket science, which in this day and age is not such a big deal.
     
  9. 242A1

    242A1 Well-Known Member

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    The exhaust system fitted to the double Kylchap P2s was never fully optimised. 2004 was fitted with an experimental exhaust bypass valve in order to minimise or reduce the amount of firebed disturbance experienced when working heavily and at log cut-offs. The thinking is that the heating of the exhaust brought about by its close proximity to the inlet steam passages imparted so much energy to the exhaust of 2001 that this is factor had a significant impact on the disturbance of the fire. The cylinders are reduced in diameter, the boiler pressure increased, the steam passages modified, ditto the valve gear. We have tools to help us predict the outcome and some engineers were very good at this but these predictions are always tested out on the road, just to be sure.

    One size does not fit all when it comes to exhaust systems, not if you wish to achieve the best optimised result. So if the system needs some adjustment there are people who can assess this and produce designs to suit. Fitting a system superior to the double Kylchap would be of potential interest. Little need to stand still. Also the volume of the exhaust beat is indicative of excessive back pressure, not something that you want.
     
  10. RAB3L

    RAB3L Member

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    Back pressure (or backpressure) is a resistance or force opposing the desired flow of fluid through pipes, leading to friction loss and pressure drop. For a given set of conditions, increasing the pressure drop will decrease the volume of the exhaust, not increase it.
     
  11. 242A1

    242A1 Well-Known Member

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    Back pressure is a pressure (force) which opposes or resists the movement of the piston due to the expansion of the admitted steam expanding within the cylinder. It is brought about by the overly restrictive blastpipe tip area, poor flow of the exhaust steam through the cylinders, valves and associated steam passages. It absorbs power and reduces efficiency. You want sufficient energy in the exhaust to efficiently drive the combustion process and little more (tapping off steam for the exhaust steam injectors). Any coal particles under 10mm in size are likely to be ejected from the chimney in an uncombusted state, hence the pursuit of GPCS as a solution to the problem. Steam locomotives ............
     
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  12. Allegheny

    Allegheny Member

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    The locomotive exhaust system is essentially a pump by which the energy in the exhaust steam pumps the combustion gases through the firebox and boiler tubes. It is inevitable that there will be some back pressure at the blastpipe for this pumping function to operate. The more advanced types of exhaust are an attempt to make this pump more efficient.
     
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  13. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    There is no "standardised LNER double kylchap" design. There's a good many slightly different iterations of this design, of which there are four generally similar types, as per below:
    • Humorist had its own a version, which was modified extensively throughout its trial period (as was its smokebox and chimney arrangements) until it was in the form that more or less formed the basis of all the classes to follow
    • The first four A4s fitted with the system were different in detail to Humorist, as they were fitted with the stovepipe style and streamlined chimneys as per their design
    • Cock O' the North and Earl Marischal
    • 5 of the 6 P2s were then fitted, with Lord President having a by-pass valve, a unique fitting that was not retained when the engine was rebuilt, and Thane of Fife being the only loco to retain a single chimney (why?)
    • The 6 P2s then received a Thompson design house interpretation of the double kylchap fitting
    • 4 x Thompson A2/1 were fitted with the same equipment
    • Great Northern when rebuilt had the same equipment
    • 15 A2/3s then had the same equipment as that fitted to the P2s
    • Bronzino had virtually the same arrangement albeit optimised per Peppercorn's design office
    • The Peppercorn A1s had a similar setup to the Thompson Pacifics and Bronzino and were their own standard
    • Then you have the Peppercorn A2s that were retrofitted with the double kylchap but married up to the fitting of the multi-valve regulator system
    • The Gresley A3s and A4s that were retrofitted in the 50s received virtually identical setups to Humorist and the first four A4s
    There are, in essence, the Gresley A3 type, the Gresley A4 type, the Thompson type, and the Peppercorn type of double Kylchap fitting. Which means, effectively, you had 78 of one type, 34 of another, 26 of the Thompson variety, and 64 of the Peppercorn setup (not including Tornado's which is very similar to the original Peppercorn setup but again has been optimised).

    Add a further complication that, in theory, you could probably by virtue of the boiler swapping that the LNER then BR (E) Region indulged with, probably find the kylchap equipment per locomotive actually found itself on different classes at overhaul time.

    All the surviving Gresley Pacifics in BR days were fitted with the double kylchap. All of Thompson's Pacifics were built with the equipment. All of Peppercorn's A1 Pacifics were built with it, but less than half of his A2s were fitted, and only one of these was standard with his Peppercorn A1s.

    Gresley understood the importance of the fitting but wanted to wait for the patent rights to expire to fit them en-masse. Thompson had that advantage, but only fitted them to new Pacifics and retro fitted one - Thane of Fife. Peppercorn's design team felt self cleaning smokeboxes were more important than the double kylchap on the A2s, but had changed their minds when the A1 was designed.

    The exacting efficiency of the draughting is not nearly as important as the fuel used or the fireman's technique (in my opinion) and whilst there's no doubt the double kylchap improved the ultimate performance of the classes described above, the single chimney versions of the Gresley Pacifics were not exactly slouches or definably and significantly less efficient than the double chimney versions.

    I remain unconvinced by the regular enthusiast clamour for more efficiency, greater performance, etc etc - these CMEs had a railway to run. Ultimately that means pulling trains: constant experimentation to get the ultimate in performance is all well and good but at some point you have to put these engines into service and let them get on with the job.
     
  14. LMS2968

    LMS2968 Part of the furniture

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    I don't know if this applied also on the other Railways / Regions, but on the LMS, when a boiler was changed at overhaul, the smokebox and therefore the chimney arrangement, stayed with the engine and not the boiler. As evidence, I would point to the Stanier Pacifics. When the streamlining was removed between 1945 and 1949, the original smokebox with the tapered top front end was retained until the smokebox became worn out. The last of the tapered smokeboxes survived to 1960 on 6246, but there had been many boiler changes in between. None of the originally non-streamlined engines ever appeared with a tapered smokebox.
     
  15. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    Unsure: but no doubt things would be examined and shopped/taken apart based on condition. My hunch - because it's based on what I've read and seen in photographic evidence of the GNR, then LNER, is that parts were regularly swapped where necessary.
     
  16. Jamessquared

    Jamessquared Nat Pres stalwart

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    I think it is probably unlikely that you would swap a blast pipe as part of a boiler swap, because fundamentally it's position, mounting etc is related to the cylinders, not the boiler. So if you don't disturb the cylinders in an overhaul, you might unbolt the blast pipe to allow access / inspection, but fundamentally I think you'd return the original. Likewise the chimney, which is positioned relative to the blast pipe. My gut feeling is that it is more logical to keep the smokebox / chimney / blast pipe together with the frames / cylinders, even if the boiler is swapped.

    Tom
     
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  17. Jimc

    Jimc Part of the furniture

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    Thinking about the practicalities, the boiler isn't going to go off to the boiler shop with smokebox and other gubbins attached. Also there are more boilers than locomotives if running a pool in the way the GWR did. So any attempt to keep smokebox components with the boiler would have required extra components that otherwise wouldn't be needed and also have to be stored somewhere.
     
  18. RAB3L

    RAB3L Member

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    That only makes sense if the rivet holes were jig-drilled. Otherwise swapping a smokebox with another boiler might be a nightmare. New smokebox perhaps?
     
  19. Allegheny

    Allegheny Member

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    I'm sure there would be a great deal of interest in any detailled record of these trials, and their findings.
     
  20. LMS2968

    LMS2968 Part of the furniture

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    Nope, I quote the ex-streamlined Stanier Pacifics again: the original streamlined smokebox lasted on 6246 until May 1960. It had been de-streamlined in September 1946 so best part of fourteen years. In between, four different boilers were fitted.

    The rivet holes were not drilled randomly but according to the drawings. These were scrupulously followed so they would line up during any change.
     

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