Under restoration/Never steamed in preservation

Those weights are the same as an old 'Railway Gazette' diagram book I have. For the locos only I make that giving weights per foot-run (over buffers) of 2.065 tons/foot for a 7200, and 1.99 tons/foot for a Castle.
Pat

 

Sorry - I wasn’t querying the weights, but whether Wiki was right on the boiler dimensions. If so, a 72xx looks somewhat under-boilered to me. I’m sure @Jimc can enlighten us.

Tom

 

My book gives very similar figures to the book of Wiki:
Heating surface - tubes (large & small): 1,349.64 sq ft; Ditto - firebox: 128.72 sq ft; Ditto - Superheater: 191.79 sq ft; Grate area: 20.56 sq ft; Pressure: 200 psi.
A bit weedy compared with, say, a Urie rebuilt D15, I'd say. (Tubes - 1,039.5 sq ft; F/B - 144.5 sq ft; S/H - 231 sq ft; Grate - 27 sq ft; 180 psi.) Power comes chiefly from the grate size and superheater area, doesn't it?
Pat

 

There's more to boiler design than the top trumps dimensions I suspect. But the Std 4 isn't the biggest of boilers, and a bigger grate would certainly have done no harm - if it could have been fitted in the locomotives it was designed for. You certainly wouldn't pick a 72 for fast vacuum freight. The 4300 2-6-0s, which had slightly smaller (18.5in) cylinders and the same boiler, were known to run short of steam given a fast timed vacuum freight and a heavy load, and I doubt the 72s were much different. The 8 coupled tanks started life with 18.5in cylinders, but were later enlarged to 19in, so clearly there was a benefit. The 28s, on the other hand, with the same wheels and a much bigger boiler, had 18.5in cylinders to the end of their lives. But given a typical heavy freight train with slow timing and the odd signal check there was all the power and adhesion that could be wanted, and the free steaming Churchward boiler would catch up. For fast vacuum freight there were the 47s, (and Castles) and there was no shortage of boiler capacity there. When it comes to 25mph preservation traffic I imagine a 72 will haul everything required on just about any line - and straighten out the track and trim the platform edges too...

 

Indeed boiler design is not top trumps, though surely the starting point for any boiler is the rate at which it can burn coal, and in that light the grate of a 72xx looks conspicuously small relative to the size of the loco. Presumably with the design duties of the original 42xx (short haul, loads tending to travel with the gradient) that wasn’t an issue - either that, or the Welsh coal had some hitherto unperceived magic calorific value ...

Tom

 

The standard 4 boiler must have been built using the same flanging blocks as for the standard 1, which no doubt saved some money. The standard 2 with a smaller boiler diameter had pretty much the same grate area as a standard 4. It is interesting to note that the boilers for the Manors (standard 14?) had a slightly smaller barrel diameter than the standard 4 but a larger grate. This was probably a more balanced design.

 

AFAICR the 72xx's were only ever really a make do solution to the withdrawal of the Aberdare's from the fleet (so slow speed plodders), using excess 42's & 52's which were stored in the depression so were never going to be perfect. The fact that they were rebuilt over a period of 5 years and lasted 30 odd years in service suggests that they did the job required of them reasonably well.

Just be nice to see one of the buggers in steam!

 

5239 seems to have done well enough on the Paignton and Dartmouth so I assume a GWR 8 coupled tank would be a useful addition to other railways' fleets too.

 

I can imagine that over a sustained period of high output that the 19”cylinders on a 72xx would be a drain in the boiler. Experience with 4270 has shown a brilliant free steaming boiler, but the design is incredibly heavy on water. Mustn’t forget also that city of Truro has a no 4 boiler And again, I can vouch for it’s steaming abilities. Boiler proportions were a big thing for churchward

 

Hence the 72xx's having water capacity of 2,400 gallons (or 2,700 with the scuttle bunker that 7200 has), against the 1,800 of the 42's, 52's. Essentially the same loco just designed to go that little bit further!

 

Indeed. In Churchward's original plan there was only one boiler for 8 wheeled engines, but weight considerations split it in two.
The reason for the Granges was because the 43s were a bit short of boiler capacity for the work they were capable of, so the Grange was conceptually a 43 chassis lengthened to 4-6-0 and fitted with a Std 1 boiler. The problem with this was weight and RA (again) though, so after various paper designs of modified Std 1s and 4s Collett eventually opted for complete new boiler, which was the Manor. Whether in practice the Manor was much of an advance on the 43 until Sam Ell breathed on it is perhaps an embarrassing question...

 

I understand that there was a proposal to turn the 72xx's out as 2-8-0 Tender loco's which might have made more sense

 

The fact that the Manor could outperform a 43 when correctly drafted suggests that the boiler design was basically correct.

 

I remember reading that 42s were being built and then put into store because the traffic they had been built for had reduced. Then some of them were taken out of store and converted to 72s. Perhaps it was just too difficult to stop the construction and build 28s instead. Was it too much trouble to go back to the board and ask for an amendment to the authorisation? The cost of building a 28 would be only a little higher if tenders from withdrawn locos were used.

 

While I'm always surprised how small the grates are on GWR No 2 and No 4 boilers, I think the property of Welsh coal wasn't so much magic calorific value, as magic resistance to clinkering. Fires in good Welsh coal could be run very deep with less fear of turning them into an enormous solidified mass in the firebox, so effectively burning a larger volume of coal on the same grate area. It's worth considering that the difference in grate area between the less-than-perfectly-free-steaming sloping throatplate Type 3A boiler on the Class 6 Jubilees, and the very satisfactory 2A on the Class 7 Royal Scots (and others), was a whole 0.25 sq ft.

 

You forget one of the primary advantages of a tankie is it is far easier to operate in reverse. With a 72xx you could run to a yard or siding which didn't have a turntable and then run back without having to worry about finding somewhere to spin the engine round. From experience I can say going tender first on a Great Western is NOT a pleasant experience at all!!
28xxs would have been better for all out power and longer runs but for doing lots of back and forth work, or for lighter jobs (72xxs generally replaced Aberdares and other similarly powered mid sized tender engines, for which a 28xx would have been very excessive). I don't think the 5205s as they were then were going straight from overhaul to storage, I think many of them had done some work and then the work dried up. No reason to cut up a brand new loco!
Besides, there must have been something right with the 72xxs, as further 2-8-0Ts were rebuilt into 2-8-2Ts to increase their water capacity.

 

I only mentioned the tanks going in to storage because I recall reading it in a book but I am unable to quote a reference. It is quite possible that some new build locos were stored before being put into traffic. My perception is that the great depression happened quite quickly and locos already under construction would have been completed but there may have been no work for them. I accept the point about running in reverse, we certainly had a lot to learn in this country about cab design before the Ivatt moguls. I was on the footplate of the Norwegian on the KESR and thought how good the design was with screen sheets behind the drivers and fireman padded seats. I even has rear view mirrors built into the fly screens. I was told that this is so you do not have to stick your head out into a snow storm.

 

As received from Norway there was also a tender cab. This was I believe removed during the rebuild of the tender.

 

Some British locos also had tender cabs, a few 4Fs and Super Ds spring to mind, maybe others

 

But have a look at say 2857 or 7812 then compare it to say 43106 or 46443, George Ivatt seemed to want to look after his footplate staff