French GWR Loco to id please

Can anyone please help me out with the id of this GWR loco please
https://railway-photography.smugmug.com/SteamMisc/Locos-to-id/NEW-GWR-To-id/i-M3ghSmN
Many thanks
Neil

 

It's either 103 or 104, President or Alliance, one of the re-boilered French compounds.

 

No 103 President - one of the three French compounds bought in by Churchward to test. In its later 1920's form with the GWR boiler.

(Or 104 Alliance - for some reason always remembered the two - La France and President and forget this one!). Its not La France because of the nameplate which was cabside.

 

Looking more closely at the photo I'd go for 104 - I reckon you can just about make out the 4 next to the right hand buffer.

 

enlarging the photo the last figure on the cab number plate looks like a ‘4’ and buffer beam 104

So 104 it is

Was it called ‘Alliance’ or ‘La Alliance’

Neil

 

Alliance.
(It would be l'Alliance anyway, but it wasn't...)

 

By all accounts the de glehn compounds worked OK.

 

Ok? They were superb!

 

The problem with all the compounds tried on Britains railways is that in general the improvements in thermal efficiency and hence reduction in fuel and water costs were less than the expense of running the compound system

 

Certainly that was the perception, although as far as I know none of the railways did rigorous or extensive enough tests to get good data without confounding effects.
It is hard to see how a four cylinder simple is much cheaper to maintain than a four cylinder compound, for example. Only an extra valve or so.

 

The de Glehn system was not fully developed at the time when the compound Atlantics were obtained for trials. The potential was there but had not yet been fully realised and you could say that remains the case.

The importance of viewing the cylinder volume to be supplied as being the sum the high and its associated low was not fully recognised and so main steam pipes were often found wanting.

Sad to say the best way of driving compounds had not yet been worked out either.

So the GW trials were never going to provide much of any value. But by the mid 1930s far more had been achieved and if the required power output of a locomotive required more than two cylinders then the view that there was then no reason not to build compounds has some merit. Looking at the way the locomotives we now have are being found wanting I just wish that we had a machine to equal the SNCF 240P in efficiency and power to weight ratio.

 

The trouble with the 240P class was that they were so powerful that they suffered mechanically. I am not sure if particular components were the problem but E S Cox states that as the 4 cylinder compounds increased in power the crank axle life steadily reduced. The problem was really lack of space for the crank webs, as the cylinders increased in size and centres the crank webs had to be made thinner to fit. Chapelon designed a 3 cylinder compound to overcome this problem, 242 A 1. This produced 5300 ihp.

 

Does this limitation also apply to 4-cylinder simples? I'm thinking that with running at a shorter cut-off , compared with a compound, the maximum forces in the rods will be greater.

 

Not in the same way. The problem is the cylinder diameter, a 240P had approx 25.6" diameter inside cylinders, which means that the distance between cylinder centres is that as an absolute minimum.

Once you've got the axleboxes and the big end journal in, there's not a huge amount of room for the outer crank web. Cox quotes about 4" thickness, I seem to recall, and for locos capable of producing over 3000 dbhp for sustained periods, that may well have been rather marginal. Strength isn't even necessarily the problem, the axle is going to flex a lot no matter what the fatigue strength of the material. A Duchess, on the other hand, has 16.5" inside cylinders, so can have considerably thicker crank webs (and is much less powerful).

The 241P class built after the war attempted to mitigate this problem by moving the (much smaller) HP cylinders inside the frames. Chapelon's 242A1 rebuild went one step simpler (despite being introduced earlier) and was a three-cylinder compound along the lines of the Midland compounds, so could have properly beefy crank webs on the single inside cylinder. However, neither of those classes would have been possible in the UK, 242A1 had 26.75" x 30" outside cylinders - and we think GWR classes have gauging difficulties...

The end of the 240Ps is somewhat shrouded in mystery; what is certain is that the line they were rebuilt for was electrified and they were all scrapped. Cox implies they'd all fallen to bits after less than 10 years service, but the cylinder dimensions and boiler pressure are not dissimilar to those on the 150P and 141P, both of which went on much longer. HCB Rogers claims that essentially SNCF organisational politics forbade their redeployment elsewhere, even when those regions were requesting them, and the new (bigger but less powerful) 241Ps were used instead. If that sounds a bit odd, consider that this is the same organisation that somehow failed to preserve one of three hundred and eighteen 141Ps, among the most efficient steam locomotives ever built.

 

I'd been interested in the simple versus compound debate, and thought that, in the long run, it just comes down to packaging the equipment.

 

The 240P design gave trouble with respect to the axle boxes of the leading bogie which were admitted to give problems due to overheating but this was simply a matter of the incorrect specification of lubricating oil being used.

Petty jealousy and politics. Those locomotive designers who were less able than Andre Chapelon were one problem, the inter company rivalries were another.

When Chapelon's designs underwent testing against engines produced by other designers the results were always interesting. Pacifics that would out perform a 4-8-2, then the 240P proving to be more powerful than best 4-8-2 that the SNCF could deliver and on to the 4-8-4 which forced the redesign of the French electric locomotives being prepared for the PLM mainline. The problem with being an outstanding individual is that few if any are less than resentful.

The 240P had one big problem. Those who resented it. True it was at the limit of what might be achieved within the classic de Glehn concept though the du Busquet low pressure arrangement might have been looking at a little more even though it gave rise to a very long front overhang on the famous Baltic design.

Chapelon did a great deal of work searching for the solution to the cylinder problem 4 cylinders were used and then 3 and then on to six. His original plan for a series of high power designs was based around 6 cylinders but the success of 242A1 caused a revision to three cylinders. The 4-8-4 was a rebuild of a failure but it confirmed the route to the 6000ihp standard designs.

In the UK the loading gauge allows little volume for the l.p. cylinders so we have to follow the de Glehn layout if we wish to readily test the compound system. Unless we can have far higher boiler pressures.

Thanks to 8126 for giving numbers that allow readers to visualise the problems.

 

One further thought. Both Chapelon and his near equal de Caso, had enjoyed a technical education at one of the Grandes Ecoles, giving them a distinct advantage over just about all their British contemporaries. Compounding evidently did demand more in the mechanical and thermodynamic fields than simple expansion.

PH

 

This discussion has started me thinking about the rebuild of "Hush-Hush". It is probably an overly simplistic question, but I'm thinking that the rebuild would have been simpler if they had retained the 4-cylinder compound drive. There must have been an advantage for changing it to a 3-cylinder simple.

 

The 3 cylinder, unified drive, simple system was what the LNER knew well. The compound mechanism fitted to the "Hush Hush" had much to recommend it but the cylinder volumes were quite modest and so the higher working pressure offered by the modified Yatton boiler was necessary in order to achieve high power outputs. The highest dbhp credited to this fascinating machine was 1702 at 56.7 mph with a drawbar pull of 5.02 tons. This was achieved on 5th June 1935 but now comes the more important information. The boiler pressure at the time was 470 psi yet the hp steam chest pressure was only 390 psi - something is wrong here, Gresley engines usually display a modest pressure drop between boiler and steam chest when working at full regulator. The hp cut off was 50% and the lp cut off 55% which gave a receiver pressure of 102psi. The maximum hp cut off used on testing was 50% and with that level of steam drop between boiler and steam chest it makes you wonder if the regulator was fully open and if it was fully open it then begs the next question. What was wrong with the steam circuit? Check out the superheater: 12 elements of i.d 1.18" for 150 sq. ft. of heating surface which gives a cross sectional flow area of 13.1248 sq. ins. Compare this figure with that of an A3; 50.603 sq ins.

To achieve the best from a compound you need to work with long hp cut offs - between 70 - 80 percent. You don't need much in the way of superheat at these cut offs in order to prevent losses due to condensing. The impact of having no hp superheat was found to be negligible providing the interstage superheater was adequate (result of tests carried out on 160A1).

Back to the rebuilt "Hush Hush". In order to produce a high powered compound the existing external lp cylinders should have been reduced in size in order to be the hp cylinders and the lp cylinders should have been places inside, de Glehn style. If it was desired to keep straight frame plates then staggered lp cylinders could have been tried.

 

It's an interesting point about the steam chest pressure, and a part closed regulator will have an effect on superheating the steam. Steam emerges from a regulator at largely the same temperature it entered, so, for example, saturated steam at 470psi will emerge at 390psi with a degree of superheat. This will make a difference if condensation in the cylinders is an issue. For the other point about the superheater cross sectional area, steam at 470psi has a significantly higher density than at 220psi.