Current and Proposed New-Builds

As a young man Model Engineer was my bible and I seem to remember reading a Quote of mr Riddles after an efficiency competition.
Clans should have been 4-8-0s caprotti and would have been world beaters.My claim is that Caprotti compounds will be even better.

 

Interesting notion. Presumably a 9F type solution would've been required for the firebox to clear coupled axles..... equalling another non-standard standard boiler!

 

Such machines were constructed by Andre Chapelon in the 1930's. Incidentally, in the post war years, Chapelon, along with the almost equally gifted Marc de Caso, returned to the use of very large piston valves on the grounds that poppet valves offered little advantage in thermal efficiency whilst being more mechanically reliable.

PH

 

I suspect the return to Walschaerts was prompted by shortcomings in both the original Caprotti design and in metallurgy back then, which produced increasing inefficiency as components wore. AFAIK, the British Caprotti development of the 1950's (as fitted to some Standard 5's and "Duke of Gloucester") wasn't used by either Chapelon or deCaso. The principal flaw with Lentz RC gear identified by A1SLT was an inability to sufficiently harden cam surfaces, with suitable processes unavailable until after the end of the steam age.

It's worth noting that P2 2007 will employ the US designed Franklin B, the rotarty driven derivative of the Lentz design. (the Franklin A derivative being an oscillating cam driven by radial gear.... e.g. Baker or Walschaerts type linkage).

Discussions on the 5AT website about radial vs poppet valves settled in favour of Walschaerts due to David Wardale's conviction that Porta style lightweight piston valves (as fitted to L&B "Lyn" and a very different design to anything which went before) answered much of the criticism of the poppet lobby, though to my mind, engineering arguments in this instance, seemed less balanced than for discussions concerning other aspects of the 5AT concept. I believe my own scepticism to be reinforced by quite so much emphasis being placed on the familiar appearance of Walschaerts over British Caprotti as a main selling point. Look at 5AT wheel and boiler designs to see why I found that argument incongruous.

 

It wasn't a return to Walschaerts; all the Chapelon poppet valve compounds were oscillating cam versions driven by Walschaerts gear. I think the reversion to piston valves coincided with double ported Willoteaux valves becoming available (which reduce the required valve travel but which Porta was later very dubious about), so as a rough rule of thumb the designs with a Paris-Orleans origin have poppet valves whereas the SNCF-era Chapelon designs have Willoteaux piston valves.

Chapelon didn't like the valve events from the Caprotti gear at the time these designs were produced, he preferred the linking of phases in the radial gears. Given the reputation of the early Caprotti Black Fives for being somewhat gutless he may have had a point; up until 44686/44687 Caprotti seemed to give its best showing on classes that had poor events and leaky piston valves in their normal form, like Claughtons. Whether the British Caprotti gear would have changed his mind, I don't know, but a compound doesn't need to run at such short cut offs in each cylinder as a simple, so the good performance on simples may not be relevant.

I'll admit that I think a well laid out set of Walschaerts is a wonderful sight in motion, like on an A3 or rebuilt Bulleid, but I don't look at 71000 and think: "You know what would make that look really good...."

 

Having checked, I stand corrected on this point. I was rather forgetting the date of Chapelon's work. Thinking of link driven OC puts me in mind of OVSB's enforced adoption of chain drive in lieu of shaft driven gear, from which it seems, certainly pre-WWII, that high spec geared shaft drives were far more difficult to produce than bog standard radial gear components. I'd imagine designing the final OC drive was a bit easier with loading gauges more generous than the UK.

I note that the Lentz installation on the inside cylindered LNER B12/2 and J20 was of the oscillating cam variety, negating the width penalty incurred on outside cylindered locos and that the Lentz fitted D49's and P2 No.2001 utilised the rotating flavour. All seem to have had Lentz gear replaced before WWII in any event (the OC Lentz gear on R&ER "River Esk" lasted only 5 years). Seemingly more successful was the 1931 rebuild of GWR No.2935 "Caynham Court", where RC Lentz gear lasted until withdrawl in 1948 (I have images of this loco at work in 1938 and 1946).

I'm looking forward to P2 2007 establishing whether the problems with the Lentz installations of the 1920's have been put to bed and whether the new build demonstrates any advantages over Walschaerts driven piston valves. If the Bugatti styled "Cock O'The North" project confounds my expectations, it would provide for a useful close comparison of the pros and cons.

As you've probably guessed, in my case, the interest is in function rather than form.

 

No .
250 9F boilers had been made already

https://imgur.com/GqDOFMW

https://imgur.com/a/lNHS1

Webb was rigth all the way

Suits diminishing loading gauges

 

As the 6MT "Clan" had a smaller boiler than the 7MT "Britannia", my thinking was that the 9F boiler would likely have been considered too heavy. In any event, had the 4-8-0 appeared instead of the Clans, assuming the same build sequence, no 9F boiler had yet been built.
Clans built 1951/2
9F's built 1954/60

Good to see someone defending F.W.W, which doesn't happen nearly often enough IMO. His compounding system was clearly a response to pressure from upstairs to keep coal consumption down, as pretty much all he did was aimed at doing just that. Sooner or later, some bright spark will return to the Webb cylinder proportions, though probably in a totally different application, and sort out any design foibles.

So far as the "pairs of driving wheels rotating in opposite directions" goes, while I'm sure they could be made to do this deliberately or due to a driver hopelessly unfamiliar with the locos, suggestions that this was a routine occurrence make no sense. An engine is either set in forward, neutral or reverse and unless I'm missing something, under what circumstances would steam from the regulator would hit the LP cylinder ahead of the HP pair anyway? The only route would be a 'simpling' valve to admit HP steam direct to the LP cylinder to get a train underway. Perhaps Webb arranged that valve was arranged to open at random times? Don't think so? No.... nor do I.

Plenty of late Victorian designs were rendered obsolete by the increase in train weights around the turn of the 19th/20th centuries, but Robert Billinton, William Dean and James Sterling (to name but three) don't suffer the ridicule aimed at Webb, some of whose simple expansion designs were among the very last pre-grouping locos in service. Certain eminent mid 20th century authors have much to answer for in my view.

 

The inside low pressure cylinder didn't have valve gear as such; there was a loose eccentric on the axle. This had a peg and slot arrangement so that rotation of the axle in one direction drove the valve directly. When the engine was reversed, the outside high pressure cylinders moved the engine in that direction and the peg would be moved to the other end of the slot, so placing the low pressure cylinder in the opposite gear and ready to receive exhaust stem from the high pressure cylinders. Obviously, there was no means of shortening the LP cut-off with this arrangement. The real snag though was that the loco had to physically move in the right direction to move the low pressure valve into the right position. If after backing on to a train, when the driver opened the regulator, the trailing driving wheels, driven by the high pressure cylinders, slipped without the loco moving, their exhaust would be fed to the low pressure cylinder, which would still be in back gear. This could cause the two driving wheelsets to slip in opposite directions.

All that was needed, and quickly provided, was an intercept valve to divert the high pressure exhaust directly to the chimney. Once the loco had moved half a turn of its wheels, the LP valve would be correctly set and the intercept valve closed, bringing the LP cylinder into action and in the right direction.

While FWW's Compounds have a poor reputation, some at least were a lot better than given credit. The poor ones were poor indeed, but the best ones could stand comparison with any other engines in the country.

 

Pedant Alert. Actually, 253 9F boilers were constructed, plus 11 Crosti boilers.

Cheers,

Alan

 

Thanks for the explaination. From my treasured (and very battered) old copy of Martin Evans' treatise on ME valve gears, I knew about the shortcomings of slip eccentric gear, use of which in anything more complex than a table-top "piddler" seems odd to me (Evans specifically mentions the Webb application). Presumably the thinking was that the key steam flow parameters were already defined by the HP valve gear, with the LP cylinder acting as it's own receiver. You'd have to rank the initial Webb layout you describe along with the lack of balancing pipes in the engine steam circuit of the prototype Merchant Navy locos. A tad embarrassing, but easily fixed.

Sounds like one for an expert on valve gears (with a passing interest in compounding and a low boredom threshold), who's also got their head round computer modelling. Unfortunately, I fall into neither category!

 

Thank You 30854 and ragl for corrections.To error in both timeline and numbers produced is consistent.
Mr Bulleid explains somewhere that the Q1 was constructed to use the very costly form parts for the boilers of 4-6-0 Nelsons.
Cox also mentions these expensive form tools as does quite some german writers.
We all know from very reliable sources that a two cylinder steam locomotive can and often did run 8.4 revs per second peacefully as carriages.
A rational standard programe would have used 5feet driving wheels only.
For locomotives where 8.4 revs on 5 feet wheels was not fast enough could be made three-cylindered.
Boiler tubeplate standard like the 9F and adjusting grate area by box length.
This would have been standardisation as it could have happened in USSR
Standard engines,nationalisation and later diesellisation looks crazy today, but one russian transport minister was shot because he found steam locomotives usefull.

 

I did warn - "Pedant Alert".......... at the time, metaphorically speaking, my tongue was firmly in cheek....... nothing but numbers after all.

Cheers,

Alan

 

If memory serves, I think it was the flanging blocks from the "Nelson" throat plate which the Q1 re-used. If I'm wrong, it still gave me a reason to say 'flanging blocks'..... so it's all good.

Don't know too much about Danish Railways I'm afraid, but I could nominate a Transport Minister or two here over the last 50 years who should've been shot!

 

MMM flanging blocks...Don't imagine theres much weight difference between a Clan boiler and a 9F. 9F has a longer shallower fire box, and tapers to Britannia diameter... but is overall at least a foot shorter.

 

You might be right about eminent authors doing Webb a disservice, though probably inevitable that a Loco Superintendent responsible for putting thousands of locos into operation will attract more analysis and comment than one responsible for a few hundred over a similar timescale.

James Stirling always seems to get a bit of a free pass. I suspect there is an element of benefiting from his brother's reputation, but in absolute terms, I don't think his locos are an especial highlight in the late Victorian locomotive pantheon, and they were shown up to their considerable disadvantage - particularly in the boiler department - by Kirtley's locos when the SER and LCDR merged. What probably saved them from early scrapping was that they were well built, and so were ripe to have their lifetimes extended by a programme of reboilering by Wainwright.

Wainwright gets little credit for that transformation: he is another of that era poorly served by later authors. His own locos combined the best of LCDR design with SER build quality, and in the process turned out a succession of excellent designs that bear comparison with most(*) other designs of that era still being built along traditional lines.

(*) Most, not all. Clearly Wainwright's designs look dated when compared with his direct contemporary Churchward - but so do those of almost every other contemporary CME. Churchward aside, I think Wainwright's locos bear comparison with any others of that era, but he rarely gets much credit.

Tom

 

Slip eccentric gear, or at least a valve gear which is always in full gear for the LP cylinder(s), sounds a good idea to me, as I struggle to see the benefit of not exhausting the LP steam fully. Cutting it off will inevitably result in higher back pressure for the HP cylinder to exhaust into. The Teutonics, with slip eccentric gear, seem to have been the best of a poor bunch.

 

Everytime I see the word Teutonic I think of Blazing Saddles.
(its twue, its twue...)

 

Sounds reasonable to me. I'm still at the early stages of trying to work out exactly what F.W.W's system was all about, so until I reach Nirvana (or at least some reasonable level of understanding), I'll sit back and devour comments by those more knowledgable than I and just ask the odd awkward question now and then!

Oh boy, do I ever agree with Tom on this one! Add Dugald Drummond to the list. But for the M7 and T9 he'd have made it with no help from me.

Agree about Harry Wainwright too. Nowt spectacular, but straightforward, competent and robust locos which looked good (in any livery as long as it was clean!) and lasted very very well. A good investment indeed for operators from the SECR right through to the Bluebell and K&ESR.

.... they're always coming and going and going and coming .... and always too soon .... right girls? (Wot? I just checked .... it's a "12A"!)

 

But the whole point of a compound is the division of expansion between the HP and LP cylinders; if the HP cylinders aren't exhausting into an elevated pressure it isn't working properly. The reason the slip eccentric gear worked satisfactorily on the Webb compounds (and the early ones did have Joy valve gear on the LP cylinder) was that massive LP cylinder, with restricted steam passages and no superheat, was no good to man nor beast once the engine got up to a reasonable speed. Keeping the admission phase long ensured maximum passage of steam through it, but without it really doing any meaningful work. At slow speed and long HP cut-offs it acted like a compound, at higher speeds it was basically a simple with a small amount of work done by the exhaust. The slip eccentric was a lot simpler than another set of Joy gear and, in the context of the Webb design, better than either linked cutoffs or independent gears set wrongly.

The whole Chapelon idea was that by freeing up the steam circuit and increasing the superheat, the LP cylinders could be made to do useful work at speed even with the HP engine notched up. For that, the cut-offs need to be somewhat in proportion, so that the HP exhaust doesn't just freely expand into a receiver which has been drained by LP cylinders at a longer cutoff - useful energy is wasted and the LP cylinder isn't working expansively. The SNCF 141Ps (which still hold the official record for most efficient steam locomotives on test, I believe) had the LP valves driven by rockers from the outside valve gear, in much the same manner as a Duchess, although a completely different linkage. That may not have been the ideal arrangement, but it was evidently good enough and probably better in less-than-expert hands than the independent cutoffs of the Chapelon Pacifics and 4-8-0s.