Edward Thompson: Wartime C.M.E. Discussion

Was it also an embarrassment for the GWR to have it hammered home post ww2 that the 'low superheat' policy was well out of date, something that even former Swindon man Stanier had recognised by about 1936?

 

I'm pretty sure that they were pretty expensive and scrapped quite rapidly. Wasn't the A2 'Blue Peter' only saved because the buyer originally wanted an A4?

 

I don't really understand what this statement has to do with the debate here - apart from trying to score points on a completely unrelated historical point?

 

I think we're drifting a bit of topic here, but Stanier certainly found the *need* for increased superheat on the LMS, but so much was different. Arguably no such *need* existed on the GWR stock in the 1930s. It would be fascinating to know why the Stanier Jubilee class clearly needed high superheat to perform acceptably, and yet Churchward's Star Class, similar in general size, clearly didn't. Will we ever know that sort of detail I wonder?

Like any other engineering decision higher degree superheat had advantages as well as disadvantages in terms of increased oil consumption, maybe even more expensive oil, lubrication problems and extra wear and carbonisation. After initially using higher superheat on his prototypes Churchward switched to moderate superheat before WW2, and incidentally introduced a massive program of superheating so I think at one stage the GWR had more superheated locos than all the other lines put together. So we can be reasonably confident that at, say, 1913 costs and technology moderate superheat was the best solution on GWR locomotives.

In 1944 we can assume that a business case for higher degree of superheat existed, because that's when the first 3 row superheat Std 1 boilers were introduced. So logically at some time between 1913 and 1944 there must have been a point where a cost benefit analysis would have shown that it was time to introduce high superheat and accept the higher oil consumption and other disadvantages. Does anyone know when that might have been? I know I haven't the slightest clue.

However if this is a genuine debate people want, then perhaps the mods would like to hive it off to a separate topic. I fear though, all it will do is continue to demonstrate how we all tend to let our pre existing prejudices and emotions overrule rational evaluation.

 

That must have been after 1929 when the german Wagner pointed at the different resistance between flues with
superheater elements and the tubes. As long as there was still a struggle with preferred draughting through the
tubes any higher superheat attempt was useless.
Kind regards
Jos Koopmans

 

I have often wondered if the inside cylinder in the Midland compounds did more or less work than the outside ones. As I understand it, the diameter proportions were calculated to deal efficiently with the pressure drop. Was any work done on relative workloads?

 

5 of the A4s had the middle cylinders lined up to 17" to reduce the loads on the centre bearings but it made no difference to the big ends and eventually 4 were changed back. that said the actual size of the remaining one is questionable, given in situ reborings at overhaul. The fact of different bore sizes makes no difference to beat. The beat is decided by the timing of the valve exhaust ports opening, not the size of the pistons.

Almost certainly the work between high and low pressure cylinders was never precisely even. The cyl proportions were sometimes changed to improve this, presumably following indicator card trials to measure how much work each cylinder was doing.

I think the GWR ran the locos with the pressure just below the redline at all times, so the lower superheat was just enough to ensure the steam stayed dry until it was exhausted. it did mean the firemen had to keep well on top of the boiler to maintain the high pressure. I think there also was something about the safety valves being able to feather at max pressure, whilst the LMS pop safety valves would suddenly open and then wouldn't shut until the pressure had dropped a long way. I can't recall where I read that, but it might come to me.

 

just to pour petrol on the fire (and im no LNER fan),

the Stanier/Cox report on further reflection shows Thompson in a worse light than before.

he failed to deal with the middle big end problem despite it being spelled out by Cox in some detail, and instead focused on a secondary conclusion of the report re the conjugated valve gear and butchered 1470 'Great Northern' etc at some considerable expense on a cash strapped LNER.

instead he could have had a chat with Harold Holcroft as to how best to deal with the valve gear, or (or both) adopted the ex GWR middle big end design used by Stanier on the LMS, which Holcroft was also very familiar with.

what he did do was not what one would expect, and merely confirms the 'prejudiced anti-Gresley' opinion that so concerned Simon, but without the prejudice!

Holcroft lived to the ripe old age of 91 and died in 1973.

cheers,
julian

 

Wasn't Blue Peter bought by Geoffrey Drury...after he purchased Bittern?

 

Since somebody mentioned Bill Harvey, I'll note that he also wrote some interesting things about the amount of work Norwich shed had to do to keep the B1s in acceptable mechanical condition when they replaced the B17s on the principal expresses. A B17 would need the trailing axleboxes refitting between overhauls to maintain an acceptable ride, while a B1 would need all coupled axleboxes refurbishing (or completely replacing) between 40000 and 70000 miles. To be fair to Thompson, this seems to have been an endemic problem with big two-cylinder 4-6-0s (Black Fives and King Arthurs, for instance) until the introduction of manganese steel liners, but it does suggest that given the methods of his time, Gresley's preference for three cylinders on even medium-powered locos may not have been so irrational.

Syncopation of exhaust beats came up on NatPres a while back, and somebody very sensibly pointed out possibility of different lengths of exhaust passages between the inside and outside cylinders. Consider a car engine, the cylinders definitely exhaust at precisely spaced crank angles, yet threes, fours, fives, sixes and eights all have different notes because of the different manifold arrangements and an older Subaru flat four warbles away in a manner very unlike an inline four. There are plenty of mildly syncopated three cylinder locos with three separate sets of valve gear; 34046 and 46115 both distinctly count to six. Four cylinder locos don't have this tendency, but they exhaust the inside cylinders near-simultaneously with the outside cylinders (with one surviving exception).

 

Yep but that was after Bittern had gone a bit wrong.

This is from wikipedia:
Bittern was withdrawn from British Railways traffic on 5 September 1966 and was bought by Geoff Drury on 12 September 1966. Bittern initially operated from York depot (site of the National Railway Museum today) on various steam charters, but the cracked frames and other symptoms of her long career soon spelled an end to her mainline career. In consequence Drury bought LNER Peppercorn Class A2 60532 Blue Peter from British Rail in 1968,[1] and this loco is still owned by the Drury family.[2]

So what I mean is, the interested parties with money at the time probably wanted A4s over the more 'normal-looking' locos. In the end we are very fortunate that so many A4s survived.

 

Umm, not as simple as that. Other posts above indicate that the LNER team did make changes to the big end bearing in the Thompson era. Clearly neither Thompson nor Peppercorn's team (presumably mostly the same people) got it right,but Thompson wouldn't be designing big ends himself. Unfair to kick Thompson any harder than Gresley or Peppercorn for the bearing's deficiencies.

Cook gives the credit for the eventual cure to changes in lubrication of the bearing as well as the shell: indeed he seems to me quite clear that he thought lubrication was the key problem. The lubrication changes o the bearings on the GWR, judging by Cook's book, cannot have been done before 1929 and were further developed later on when they developed manufacture techniques that allowed finer tolerances. Holcroft most certainly wouldn't have seen the new bearing design because he had left the GWR before the Great War, and its also possible it might have post dated Stanier, who left the GWR in 1931. It certainly seems likely the ultimate design post dated Stanier.

There's one amusing sidenote in Cook's book about the bearing development. The new design had a pipe leading down to the bearing for oil, at which point the oil was distributed by a felt pad. Traditionally bearings had always had "trimmings" of wire and yarn which I assume the oil flowed down, and drivers would change these as they felt necessary. It was essential that such trimmings didn't go in the new design, so they put in a fluted plug in the pipe which allowed oil to flow freely, but prevented the driver from putting in a trimming. Needing a name, they called the plug a restrictor. As Cook tells it an ex-apprentice who had gone on to work for the LMS, when visiting Swindon told a foreman they were in a fool's paradise: the LMS had made tests and found that the restrictor didn't alter the flow at all. "In reply to which he was told that it was not intended to - it was there to restrict some fool from putting in a trimming."

Holcroft, in his books, is quite silent on the demise of the conjugated gear on the Southern. I haven't spotted anything in which he comments on why it was dropped, or whether he agrees or disagreed with the decision. But clearly in Maunsell's eyes Holcroft hadn't got conjugated gear working satisfactorily either.

The Don Ashton valve gear papers I linked above indicate that it is very difficult to fit in a centre set of valve gear that has exactly the same properties as outside ones. Whilst greatly admiring the work of the Peppercorn team he notes that the centre cylinder on the Peppercorns will still be worked slightly harder than the outside ones at speed.

One of the worst examples was apparently a Pickersgill 4-6-0 for the Caldedonian which had Walschaerts gear outside and Stephenson inside. That must have made a most remarkable series of beat changes as the driver linked up.

I think you'll find that's because the crank angles are quite different on the different cylinder arrangements, (and different again in V as against in line engines) and different again on the flat four. With bike engines (which I have some experience of) I don't recall ever detecting any difference between an in line 4 with headers of varying length against those with identical length headers. Obviously a lot more difficult to pick up irregularities in the rhythym of an engine doing 10,000 rpm...

 

Yes, the crank angles are different, but the timing interval between exhaust events is identical between all the cylinders of a given engine, it's 720/x (where x is the number of cylinders). How they interact with the headers and other cylinders obviously does change. Five cylinder engines (and the Subaru flat four) often sound quite offbeat, and yet the firing intervals are even, by locomotive standards the valve timing is perfect. My point was that engines can sound quite syncopated and uneven while mechanically being entirely regular, due to the influence of the exhaust system.

 

i am surprised that Jimc hasnt mentioned this but GWR locos were set with the valves to give even cut off and exhaust points. this wasnt, so far as im aware, the practice of other companies. the GWR valve gears both 2 cyl Stephensons and 4 cyl Walschaerts were worked out meticulously thanks to Willie Pearce.

the synchopation and over-running of the inside cylinder valvegear were noted early on by Gresley on his conjugated gear.

Holcroft did work out a conjugated gear for a 4 cyl loco which was applied to at least one loco - any of you know which was the first to be so fitted?!

Holcroft kept in close contact with subsequent developments at Swindon as did Pearson after they both left to join Maunsell. Holcroft got lots of stuff from Swindon when on the SECR and SR.

cheers,
julian

 

Thank you for resurrecting my earlier comment: - Considerable work was done on this matter by RAW Meiningen when they created 18 201, and anyone who has heard this superb loco ("The world's fastest serviceable steam loco"!) will agree that its exhaust sound is unique.

Incidentally, the ÖBB (Austria) operated many 2-cylinder compounds, whose exhaust notes were also unmistakeable.

 

Quite a lot there seems to be missing the point. Nobody "solved" the problem of the middle big end - it is still a perennial and potential fault on conjugated valve gear locomotives. What has changed is that the way it is maintained, and the keeping of its overall mechanical condition. Proving - as per many sources, that insomuch as prewar was concerned, conjugated valve gear was absolutely fine given decent standards of maintenance.

The report doesn't make conjugated valve gear a "secondary" conclusion at all - points one and two of its conclusions are entirely regarding the conjugated valve gear, so how you arrive at that is, I'm afraid, a show of your bias somewhat.

The use of the term "butchered" - a very emotive term - is applied because you aren't thinking about what the report suggested and what Thompson subsequently did as a result. Cox suggested locomotive types could be rebuilt with a third walschaerts gear. That's exactly what Thompson did - to class V2 in the A2/1 and A10 with the A1/1. Perfectly within his rights to do so, he had an independent report which suggested he do so.

Lastly - no, it shows Thompson in a better light. He has always been accused of wanting to destroy all things Gresley - without evidence and always as some sort of irrational hatred - here we have evidence that he wanted to change things and was perfectly in his rights to do so based on the evidence available at the time. The report in its language is damning of the conjugated valve gear and the middle big end design, frankly.

You point the finger at Thompson for not sorting the problem out but Gresley was still building new locomotives with the conjugated valve gear despite these problems becoming greater during the early years of the war. Six times the number of middle big end failures in the last year of Gresley's reign as CME compared to comparable failures on the LMS is an incredible statistic.

The cost of converting Great Northern was no more expensive than any rebuild and was probably in fact cheaper than any of the prototypes Gresley produced previously - it used a large number of standard components including those developed for his previous Pacific classes and a standard A4 boiler. It reused components of the original, and other components from the dismantling of the original went into the spares pool. So "at considerable cost" is in effect completely incorrect.

 

The gear as such is NOT the problem, it was the big end design but that wouldn't fit in with a revisionist history of ET and your damnation of the Gresley derived motion. How many times must it be said that once a satisfactory big end was designed and fitted, the middle big end problem became greatly diminished?
As for saying the gear is still a potential problem, how many middle big ends have Gresley three cylinder locos suffered problems with in preservation? Any middle big end is a potential problem irrespective of the gear used.

 

I believe that is exactly what I just said. Your overly aggressive responses accuse me of revisionist history yet the evidence is right in front of you.

I have said it a number of times: I am not condemning the conjugated valve gear either but the evidence is there to suggest that Thompson was within his rights to abandon it. That's not revisionist at all and is borne out by the facts and by the report Cox and Stanier gave. The issue is not whether it works in theory or practice: at the time it was not giving adequate service to the LNER and Thompson, supported by the report, abandoned it on all new LNER designs.

That the problem became diminished once maintenance levels were improved is not entirely irrelevant but it is missing, once again, the context of what I am saying.

I have just said that the middle big end is still a problem on conjugated valve gear locomotives - you've just confirmed that with your last comment. And I quite agree, it is irrespective of the type of gear used. So we agree on that point.

So effectively you have just been particularly nasty and aggressive because you seem to think there's an anti-Gresley bias going on here. There isn't. But read into my comments as you so wish - it reflects badly on you, not me.

 

I might add, is it any wonder that discussion of Thompson is difficult when there is such tribal aggression at looking at the facts in an objective manner. I thank those of you who continue to post with some respect for others and only ask that that continues.

It is interesting that - as commented previously by other posters - the most aggressive posts come from Gresley and Bulleid supporters. I suspect such misplaced anger comes from a belief that their reputation is being tarnished. It is not - but then objective viewpoints which might betray some critical analysis never sits well with the extremes on one side or the other.

 

Re 18 201, the exhaust on this sounds like a mechanical knock, but suspect it is merely a resonance due to the exhaust passageways layout.