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Bulleid Pacifics - Past or Present

Discussion in 'Steam Traction' started by 34007, May 13, 2008.

  1. Bulleid Pacific

    Bulleid Pacific Part of the furniture

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    Regarding 34092, one can never say categorically that it will never run on the mainline again, but the principal thing it needs at the moment is certainty.
     
  2. DismalChips

    DismalChips New Member

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    Wells being the engine that got me back into all this and that reignited a childhood obsession, I think I'll bung a few bob her way.
     
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  3. Andy B

    Andy B Member

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    Thought I'd just post a couple of pictures I took yesterday at toddington of the underside of 35006. It's readily apparent the amount of holes in stretchers and brake cross beams to keep the weight down. Basically anywhere they could drill a hole they did!! First picture is looking to the rear. (The bogie central pin can be seen) whilst the second picture is looking forward from the rear drivers.
     

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  4. 8126

    8126 Member

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    35006 is of course a first-series MN - 21C1 came out rather alarmingly overweight, hence the surgery on it and the rest of the batch. Second and third series had the re-designed, lighter boiler so I believe the level of hacking around of the frames was reduced, although oddly it wasn't unknown for a first series boiler to turn up on one of the later locos.

    Interestingly, 15 years earlier I seem to recall 850 had a lot of work done to keep the weight down during building, including machining of surfaces that would normally be left as-cast. Of course, it promptly turned out lighter than expected and the production Nelsons had a rather more relaxed approach taken.
     
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  5. Bulleid Pacific

    Bulleid Pacific Part of the furniture

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    The issue was probably because weight was just as much a concern for George Ellson after Sevenoaks as the use of 2-6-4Ts at speed. Ellson retired from his position in 1944, so would have had some influence over the final weight of the locomotives, having already vetoed a 2-8-2 design by Bulleid.
     
    Last edited: Nov 14, 2017
  6. 30854

    30854 Well-Known Member

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    IIRC, wasn't Ellson was happy with a 2-8-2 with the proviso that it had a leading Krauss-Helmholtz truck, which Bulleid then vetoed?
     
  7. Bulleid Pacific

    Bulleid Pacific Part of the furniture

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    I was under the impression that Ellson was completely against eight-coupled passenger locomotives. I should have access to my sources later today to check.
     
  8. Bulleid Pacific

    Bulleid Pacific Part of the furniture

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    Ellson was happy for a couple to be built for trial purposes only, leading Bulleid to forsee 'more arguments than engines", which prompted him to pursue the Pacifics instead.
     
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  9. 30854

    30854 Well-Known Member

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    Thanks. I didn't know the specifics, but a limited test build makes perfect sense. I think my own recollection was from a library copy of 'Last Giant of Steam' (someone obviously hadn't heard of Ing.L.D.Porta!).

    Not too sure what OVSB's objection to the K-H was, as they were employed on quite a few designs, including some with a turn of speed and seem not to have caused any serious issues. Not knowing when it was patented (Richard von Helmholtz retired from Krauss in 1917, so any offers?), I imagine it's a possibility that the idea of paying royalties on a still current (they can get updated, which resets the date) German patent was a no-no by the time the MN's were first mooted in the run up to WWII (the events of the Anschluß and Sudetenland were very prominent in everyone's minds at that time). If that was the case, perhaps the LBSC experience of contractural issues concerning the Siemens technology with their OHLE, or the SECR with their Borsig built L class was a consideration, or perhaps, having been HNG's padawan*, he just didn't like any form of articulation.

    *Wot? You've never watched 'Star Wars' ?
     
  10. 8126

    8126 Member

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    The Krauss-Helmholz and Zara trucks are both very nice solutions in the narrow technical sense of giving a flexible chassis, however both require the cylinder centres to be pushed out. That might have been OK on the Western section, home of Urie locos with 22" cylinders, but possibly rather less practical on the Eastern section.

    Bulleid clearly wasn't a believer in trials, see the Leader, but in this case I can sympathise with his view. Firstly, if you want to get building quickly they add delay, whereas the 4-6-2 design had no such restriction. Secondly, there's danger if you can't get the gatekeeper to provide a definite specification for what success looks like. The engine is built, the CME department thinks it's all very fine, but the Civil Engineer says no. Back to square one. Nowadays it's possible to put a lot more instrumentation on a vehicle, allowing hard acceptance criteria to be set. Not quite so viable then.
     
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  11. 30854

    30854 Well-Known Member

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    Interesting considerations. What would the CME's of old have given for today's computing power, eh?

    While I get your drift, I'd point out OVSB conducted pretty extensive sleeve valve trials on H1 No.2039 "Hartland Point", which if nothing else gave his brother-in-law George Ivatt (present at the first trial) a good laugh, at the same time as conclusively proving that using sleeve valves still meant piston rings were neccessary.

    Over on the CIÉ, in 1952, 2-6-0 No.356 was heavily modified in association with trials ahead of "Turf Burner" CC1. I don't think that, in either case, the operating departments were too happy to lose useful locos.
     
  12. 8126

    8126 Member

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    You're quite correct, I should have thought of those. However, in those cases Bulleid was defining success, or at least not having to persuade a Civil Engineer with a strong reason for being averse to the particular design feature.
     
    Last edited: Nov 14, 2017
  13. Jamessquared

    Jamessquared Resident of Nat Pres

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    I'll throw this out as a hypothesis, (in defence of OVSB), rather than as fact I have any proof for.

    A criticism of OVSB is that he plunged headlong into radical new designs, rather than going through a cautious process of design evaluation of a prototype first. Had he been more cautious, maybe he would have accepted the chance to design a pair of 2-8-2s and develop them before series production.

    However, imagine it in the context of a wartime CME. There are plenty of examples in weapons manufacturing where designs that subsequently proved flawed, sub-optimal or whatever were nonetheless build in some numbers quite rapidly. If you are fighting a total war and think you have a winning design, spending a year or more finessing it may be unnecessarily dilatory when the requirement is just for more - fast.

    So I wonder whether there was a sense with Bulleid going straight to series production of his engines in the early part of the war (successfully with the Q1, perhaps less so with the MN) that the need was to get something out now, rather than spend three years working the bugs out to get a better product but too late. If so, it would hardly be the only example in the war when speed from drawing board to front line was more important than almost anything else. You might add the MNs in particular to the same pressures that delivered hundreds of Westland Whirlwinds, Avro Manchesters and other such near-misses.

    Maybe isn't the only reason for how he acted (I'm sure suddenly becoming a chief after many years as a technical assistant may have given him a feeling of perhaps needing to seize his chance while he still had it) but I am sure that the pressures of the times must have made being in a headlong rush easier to justify, if nothing else.

    Tom
     
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  14. Bulleid Pacific

    Bulleid Pacific Part of the furniture

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    I buy that. It's essentially what I think, too. I'd speculate that whilst the Nellies were good in the right hands, their reputation as being, shall we say, 'picky' in the hands of less experienced crews preceded them. Presumably at the time Bulleid took control, train weights were regularly getting pretty heavy, requiring a locomotive that could deliver the goods under all circumstances, rather than if and when it had crews who knew the idiosyncrasies of the firebox. All speculation on my part, though.
     
  15. 30854

    30854 Well-Known Member

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    Sounds plausible enough. Certainly later design aspects would've been developed during war years, though AIUI the germ of the express ..... sorry, heavy mixed traffic design was quite a bit earlier.

    Of one of the principal achilles heels, the valve gear, my understanding was that Southern internal politics forced adoption of the Eastleigh pattern reverser over the Ashford design, which by general consensus seems, then as now, to have been regarded as the better of the two.

    Regarding the other big problem, the chain drive, I wonder at what stage Bulleid's (reasonably well attested) preference for shaft drive had to be set aside? Given his earlier LNER experience with shaft driven Lentz valve gear, I can well believe a familiar component would have been first choice, with chains an unfortunate but neccessary wartime expedient.

    I've always thought criticism of the concept of the "oil bath" rather unfair (even if valid in practice!), my understanding being that the fairly new technique of welding pioneered at Eastleigh was insufficiently well understood anywhere at that time, so as Tom mentions, under wartime conditions prevailing during construction of 21C1, there simply wasn't the time to adequately test the prototype for long enough to identify problems which were caused by welding differing steel sections. When you look at contemporary shipbuilding, you soon realise Bulleid wasn't alone in this. The book on welding was being written at Eastleigh! I wonder what changes the folks unrebuilding 35011 will find neccessary in this portion of their project?

    From a layman's perspective, thermic syphons look to have much to commend them in terms of improved boiler circulation, but I'd be interested to know if those with first hand experience of maintaining the Bulleid boiler feel that there's sufficient benefit to outweigh the additional complexity? Do the syphons have a significant staying effect on the flat surfaces of throatplate and top of firebox? The thing which gives me pause for thought is that syphons didn't feature on the BR "standards". Did earlier experience of syphons on the copper firebox of V4 3402 outweigh that with the all-steel Bulleid boiler? Or did something happen around that time at Crewe I wasn't aware of?

    The loss of route availability (of the light pacifics) along with the balanced motion during rebuilding is an area I feel Bulleid's critics tend to underplay and although rebuilt MN's perormed the same service as before, introducing hammer blow into the design must've had a cost implication in PW terms.

    Oh yes ...... and I rather like the look of those BFB wheels. Don't panic, I wouldn't look to retrofit them to anything which went before!
     
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  16. Bulleid Pacific

    Bulleid Pacific Part of the furniture

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    There are some sources (Day-Lewis, I seem to recall) which appear to imply that Bulleid, having transferred to the Southern, discussed fitting thermic syphons with Gresley, who promptly fitted them to the V4. I don't think they are complex; they are indeed prone to corrosion or cracking, but these issues can happen elsewhere on any firebox.
     
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  17. 30854

    30854 Well-Known Member

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    Every worn syphon I've seen removed seems to be "gone" in the same place, the angle on the outside (backhead) edge, which suggests to me that this area is vulnerable to both heat and scouring. How long did they last in 'big railway' service?
     
  18. torgormaig

    torgormaig Active Member

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    I think you will find that V4 3402 had a steel firebox with a single syphon. As far as I am aware it was not possible to fit syphons to copper boxes which is probably one of the reason that they were not considered for the Standards .

    Peter James
     
  19. Jamessquared

    Jamessquared Resident of Nat Pres

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    That's been discussed before here, but I'm afraid is a bit of an enthusiasts myth.

    Firstly, the reverser used wasn't pure Eastleigh (nor pure Ashford): it was a development that included elements of both designs.

    More pertinently, the same design of reverser was used reasonably successfully on both the Q and the Q1, which shows that there wasn't a fault with the mechanism per se.

    The key issue is that, as with any steam reverser, maintenance is key to ensure that the locking cylinder doesn't leak. Any leaks there will mean that the device won't reliably lock, but instead there will be play as any air gaps in the cylinder are taken up. The big problem on the Bulleid pacifics was that the reverser was located in a very constricted position, where maintenance was awkward and therefore tended to be skipped. By contrast, the same reverser of a Maunsell Q sits on the running plate and can be easily got at: on those locos, the reversers did not attract the same level of disapproval.

    There is a second issue, which is that the valve gear on a Bulleid is very light, so tends to move very quickly. That problem was exacerbated by a steam valve that was, originally, fully open or shut, meaning that the initial movement of the gear was very fast, which limits precision. To some extent, that was corrected by a later modification to add a pilot valve, allowing the first movement to be slower and more controllable. (That modification was recently applied to the Maunsell Q at the Bluebell).

    The bottom line is that the key problem is the position which inhibits maintenance. Moreover, using any steam reverser makes it difficult to drive using a "full regulator, subtle changes of reverser" driving style, as is normally advocated for large superheated engines. Both of those are essentially a consequence of using a steam reverser, which was a compromise Bulleid felt he had to take when a satisfactory arrangement for a screw reverse couldn't be arrived at. It's not a question of "Eastleigh bad, Ashford good" then swallowed up by internal drawing office politics.

    Tom
     
    Last edited: Nov 15, 2017
  20. 8126

    8126 Member

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    While the weight increase on rebuilding was certainly a limitation, I'm fairly sure the introduction of hammer blow is a myth, although repeated in several sources.

    What was changed was the introduction of a balanced crank axle, as the final response to the Crewkerne incident. That meant the outside rotating masses also had to be balanced (having previously contributed to balancing the crank axle), hence the big balance weights on the driving wheels only of a rebuilt Light Pacific. If they'd been introducing reciprocating balance, it would have been spread over all the axles to distribute the hammer blow. Yes, the Merchants gained visible balance weights on all coupled wheels, but that's because of the heavier coupling rods they gained around that time, which are pure rotating mass and do not contribute to hammer blow.

    In fact, all Bulleid Pacifics have balance weights in all wheels, it's just that on the originals they're sufficiently small that they're hidden in the pockets of the BFB wheels.
     
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