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V4 2-6-2 No. 3403

Discussion in 'Steam Traction' started by Foxhunter, Jan 30, 2018.

  1. 8126

    8126 Member

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    I think you're being a bit parochial in your dismissal of the monobloc there. If removing the cylinders from the frames was so important, cast steel beds would never have taken off; put another way, if the cylinders need removing from the frames as a matter of routine something is wrong with either the cylinder design or the frame design. I believe the Urie group reckon they're the first people to remove the cylinders from 30506 since it was first built, and primarily because of corrosion problems rather than any fundamental weakness.

    The monobloc can be considered an interesting move in the direction of cast steel beds or Chapelon's proposed fully welded frames; take all the forces due to the engine and tie them together in a single solid component. If the monobloc castings were causing trouble, the problem was with the casting design rather than the concept.

    As for them not being used on the LNER after Gresley, the monobloc is really constrained to classes with leading pony trucks, since Gresley Pacifics have the inside cylinder pulled well back and subsequent Pacific classes have it pushed well forwards. No new multi-cylinder classes with leading pony trucks were introduced after Gresley's time. I suppose you could do a 2-cylinder monobloc, which would be a logical progression from the GWR's American-inspired arrangement of two cylinder castings bolted together and forming the smokebox saddle (which presumably also required a boiler lift for removal). Now, a fully cast or fabricated front end, with the main frame plates welded on at the back, that would have been an interesting design for a Pacific...
     
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  2. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    So to clarify: you call me parochial and then immediately post something which agrees with my view.

    Hmmm!
     
  3. Steve

    Steve Part of the furniture Friend

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    The raison d'etre of Green Arrow being preserved and not another V2 has nothing to do with the monobloc; it is simply because it was the first of the class. Except for the obvious, such as Mallard, the principle employed when the original list was drawn up was to preserve the first/oldest of the class where these were still in service.
    As to whether it will steam again, in the end it will come down to the people with the power and their view of such things. These will quite probably change over time, as do opinions in the museum world. It has nothing to do with uniqueness.
     
  4. 8126

    8126 Member

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    I'm saying that you're viewing the monobloc in a purely LNER/BR context, rather than in the context of steam locomotive development as a whole, in which the monobloc is more representative of the ultimate line of development than separate cylinders. The reasons for its use not being continued on the LNER are specific to that line and application. So yes, a little parochial...

    I'm not sure about @Steve 's line about Green Arrow being first of the class being the sole reason for it being selected. King Arthur was set aside for preservation but then scrapped due to lack of originality; in this case the Drummond tender had been replaced with a Urie-pattern example in its last years of service, so Sir Lamiel was preserved, being largely in its as-built condition (which ironically included a Urie-pattern tender). 30453 was apparently pretty knackered, but that didn't stop the NRM's Crab being preserved.
     
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  5. The Green Howards

    The Green Howards Part of the furniture Friend

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    I remain unconvinced; I still say the monobloc was the influencing factor. I am sure there are other locos in the National Collection that are neither first nor last.
     
  6. 242A1

    242A1 Member

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    Francis Webb was, so far as we are aware, the first to identify the advantages to be obtained from a steel mono-block construction. Was Gresley made aware of this whilst at Crewe?

    The LNER constituent companies did have some experience in producing cylinder mono-blocks but there was neither the capacity nor the knowledge to allow the company to go beyond this. The US builders in their drive to build the best mechanically designed locomotives in the World were another matter.

    The Americans wanted high utilisation, they needed far bigger engines than we used here - they needed far more power. And so they designed and built accordingly however the results of their application can be witnessed rather closer to home. There were some variations but the 141R is well worth looking at. It is an American locomotive on a smaller scale than was usually found in the States.

    Why build a locomotive using far more parts than required to deliver a core component? In this case the frame structure which in traditional UK practice consists of a number of parts held together with many hundreds of bolts and rivets which seldom proves to be quite rigid enough or quite fatigue failure resistant enough. And how frequently did the fasteners prove to be in need of attention?

    Chapelon admired the positive aspects of the cast steel bed but devised a method of achieving the same result for less weight by means of welding tubular sections which could be used to provide air tanks, large lubrication tanks and maybe other things.

    So there was a movement in the railway world to improve frame structure design and this was not going to be done by continuing to bolt and rivet numerous modestly sized parts (compared and contrasted with the whole they were modest) together to make up a whole which if well designed should never need dismantling.

    The V2 design should be viewed in context. The cylinder block was not fully satisfactory in that failures were experienced. It should not have needed replacing, was there a foundry problem, was something overlooked at the design stage? We don't know, not yet.

    No one with expertise in modern cast iron welding repairs has inspected Green Arrow, no one knows if a repair is possible or not.

    And yes, the engine was selected for preservation not only because it was the first, it also remained largely as designed.[/QUOTE]
     
    Last edited: Sep 10, 2018
  7. 242A1

    242A1 Member

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    If you get the chance talk to David Elliot about the divided drive, inside cylinder "pushed we'll forwards" and frame movement.
     
  8. toplight

    toplight Member

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    The situation with locos in the 1960s when they were selected for the national collection was at the time they wanted locos that were in original condition and also ideally the first one of its type, (or one with a famous history like Mallard), so the monoblock cylinder would have been preferred simply because it was how they were originally.

    If you look at this NRM document, it says:-

    "The main disadvantage of the monobloc casting was that if only one of the three cylinders cracked or was otherwise damaged, then the entire unit would have to be replaced. In 1955 on the grounds of expense the Works Manager at Darlington suggested recourse to three separate cylinders, which was agreed. During 1956-1962 many of the class (about one third) were rebuilt with three independent cylinders, which were then distinguished by the provision of outside
    steam pipes. No.4771’s ‘card was marked’ to preclude this modification from being made, so pre-war LNER apple green livery can validly be worn"

    It also gives the advantages of the monoblock if you read it.

    So in other words, they had probably decided already to preserve it and therefore deliberately didn't fit the separate cylinders in order to keep it in original condition.
     

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  9. MellishR

    MellishR Well-Known Member Friend

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    How did the V4s manage to have better RA than the B1s? They have the same number of wheels, and one might expect the V4's wide firebox to be a tad heavier, likewise the three rather than two cylinders.
     
  10. 242A1

    242A1 Member

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    It is lighter, the design used a number of welded rather than cast components, 5'8" wheels are significantly lighter than 6'2", the cylinders are smaller and of a newer design (the cylinder design fitted to the B1 basically dated back to the two cylinder 2-6-0 types) and it would be useful to know exactly how the totals (3 x 15" x 26" c/w 2 x 20" x 26") differed the V4 could be little heavier here, it might even be lighter. We will get to know far more as the build project progresses.
     
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  11. 8126

    8126 Member

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    Also worth remembering that most civil engineers would give 3-cylinder (and 4-cylinder) engines a bit more leeway on the static axle load compared to two-cylinder engines, courtesy of the reduced hammer blow. An original Bulleid WC/BB also has better route availability than any Class 5 4-6-0s.
     
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  12. W.Williams

    W.Williams Well-Known Member

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    Interesting discussion. It's amazing what can be done with weld repairs now. I'd be surprised if the cracking on the V2 was so bad it couldn't be repaired.

    The key issue with large castings like that is the cooling of the cast and the quality of the feedstock.

    Feedstock has moved on light years since then and so has the understanding around the cooling requirements.
    Contaminants of any kind aren't great in a cast. In the 30s the steel just won't have been that clean.

    A large cast lump will always have some residual stresses due to uneven cooling because of the geometry. I highly doubt any heat treatment was done at manufacture to remediate this. This however is the exact same problem with a weld repair, residual stresses once in can be mitigated but rarely entirely removed. Weld a big crack and you are adding residual stresses, it may crack elsewhere later. Ideally you want to take them out as best you can using a post weld heat treat.

    Lots of heat jackets can be used, but really it's a bake in the oven for 6-8 hours at 600 or so to make a go of it. Who has an oven big enough?

    Then there is no guarentee it won't have moved and the holes no longer line up. Then there is the NDT. Would the old one pass a pre-weld DP inspection....??? That's Pandora's box.
    I bet there is cavitation in that cast! How much grinding back do you do before you scrap the block?!

    Then it has to pass post repair DP aswell. For all that hassle, you might as well just cast a new one. At least a new monoblock is a known quantity.

    Who could cast a new one? Forge masters in Sheffield seem an obvious candidate. There must be others, Port Talbot? Either way, weld repair or a new casting, it's going to be expensive!

    Reading through this, it's clear Green Arrow has value in retaining her monoblock. It is historical. Would we strip Mallard of her Bugatti coat?!
    I think you have to keep the monoblock.

    Looking at some of the US Designs, it is clear you want large castings to replace fabrications or smaller castings where possible. It does add stiffness and reduce part count. But they require significant capital investment in equipment to cast and machine. How typically British we didn't follow suit and invest, then again our engines are no where near as powerful.


    Back to the V4. She doesn't have any of this to worry about. I'm at a loss as to why go for a different valve gear to what Gresley designed. Have any of the conjugated gears caused problems in preservation??

    Also, what is an estimated finish date? 2025?
     
    Last edited: Sep 11, 2018
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  13. Hermod

    Hermod New Member

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    Was the monoblock cylinder group cast iron or steel?
     
  14. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    You'll forgive me I hope, but in context of wider development and not just on the LNER, the fact that Green Arrow is a prairie tender engine is by far more important than the monobloc, which was an engineering dead end so far as the LNER were concerned.

    Throughout the world, there were questions asked of locomotive availability. This was down to a number of factors, including but not limited to the simplicity or otherwise of disassembling a locomotive for overhaul or working on specific parts of it.

    The monoblocs on the LNER were built just pre second world war, during the second world war, and immediately after (as this was the trend when V2 building was continuing from Gresley to under Thompson). Yes, there's likely to have been problems with both the material grade used and the castings themselves - there was a war on and there was a distinct and notable (and noted) shortage of workers with the necessary skill sets, on the LNER.

    That they were found wanting is not unsurprising and the very fact they were later removed as and when required probably confirms it was the V2's one, rare, weakness. They were still the most successful prairie tender locomotives in the British Isles, one of the most numerous classes on the LNER and I suspect one of the LNER's highest revenue earning classes, if you look at the work they did.

    I think trying to claim Green Arrow's least defining feature - the monobloc - as somehow representative of monoblocs elsewhere (who else used a monobloc mated with conjugated valve gear? Don't think there are other examples of this?) is missing the point of Green Arrow spectacularly. She represents one of the last successful applications of Gresley's design ethos. Of the parts that make up the whole, I will happily go on record and say I don't think the monobloc represents developments elsewhere nor does it reflect LNER practice. But if it helped save her for preservation? All the better.

    In the meantime I had a chat with another one of the V4's supporters yesterday and I feel that this could be the new build that surprises us all, in a good way.
     
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  15. Jimc

    Jimc Part of the furniture

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    I believe (subject to correction) that the extension frames and cylinders could be removed as a single unit without lifting the boiler, which would be supported on the brackets supplied as extensions of the motion plate. I don't know how useful this was in practice when all the facilities were there to lift boilers though.
    Cook tells us that they ended up having a complete assembly of cylinders and extension frames prepared, so that if a locomotive required new cylinders the old assembly was removed and the new one bolted on, reducing the overhaul time.
    Isn't it a little simplistic to suggest that one factor or another was critical and discard the others? In the formal over-bureaucracy of these days each factor would be given a points score on a score sheet, and the one with the best points total wins. In the early 60s I doubt they were so formal, but the same principal applies. Its reasonably well established that the early preservationists favoured 'originality' to a much greater extent than the current generation does, which tends to emphathise 'authenticity'.
     
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  16. MellishR

    MellishR Well-Known Member Friend

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    Now you're doing what others here get castigated for; dropping a hint about something you've heard and leaving us guessing. What could it be? Porta modifications? Monoblock (after and despite the decision for the P2's cylinder block to be built up in sections)? Whole thing finished ever so fast? (These specific suggestions not to be taken too seriously!)
     
  17. Jamessquared

    Jamessquared Nat Pres stalwart

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    I suspect you are reading a bit much into @S.A.C. Martin 's comment - I read him to mean simply that the finished loco may offer a level of performance that belies its size.

    Tom
     
  18. W.Williams

    W.Williams Well-Known Member

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    It’s obviously that the V4 has a secret benefactor and is half funded already and 1/4 of the work orders for parts are already out the door and Bantham Harrier is the name and she will be running before the p2.
     
  19. Jamessquared

    Jamessquared Nat Pres stalwart

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    I think in your effort to downplay the engineering significance of the monobloc cylinders, you are rather over-egging the case for the fact the loco is a 2-6-2 tender engine. That wheel arrangement is hardly mainstream in British loco practice and I suspect wouldn't on its own be a reason to preserve the loco. The fact that "Green Arrow" was the exemplar of what became a very successful class of locos is reason enough to preserve it, but that would probably have been the case regardless of the wheel arrangement. Indeed, from both the LNER's later point of view, and that of wider British locomotive engineering practice, a 3 cylinder 2-6-2 tender engine was every bit as much an engineering dead end as the precise concept of the cylinders.

    (Side thought, to which I don't know the answer: some World War II tanks had large cast hulls. Did the expertise of different railway workshops in making large castings and / or large fabrications influence who got which contracts for specific armaments production during the war?)

    Tom
     
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  20. 240P15

    240P15 Well-Known Member

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