• Comparative 4-8-4 data... please?

  • Discussion of steam locomotives from all manufacturers and railroads
Discussion of steam locomotives from all manufacturers and railroads

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  by Allen Hazen
The recent (on sale late 2011) "Classic Trains" special on 4-8-4 locomotives got me curious. It contains tables with some dimensional information on most North American classes, and a photo of a fan trip in the Ukraine with double-headed ex-Soviet P36, but no data on these. Does anyone here have data (weights, driver diameter, cylinder dimensions, boiler pressure, any sort of boiler dimensional information...) they'd be willing to post on some non-North American 4-8-4 types? Two I'd be particularly interested in are the Russian P36 and the South African 26 class. (Which of these two, for example, is the bigger and more powerful? South African Railways are narrow (3'6") gauge, but the 26 is a very large locomotive for that gauge, and the P36, though built for 5' gauge, is quite tiny by North American standards....)

And one that was never built: I recall seeing that a 4-8-4 was proposed for one of the big pre-nationalization British railways. Does anyone have any details on this?


To get things going, I'll try to post something-- what I can find on-line-- about the P36 over the next few days. (Wikipedia has a bit, a preservation group that owns one has some more, and Wikimedia has a diagram with some dimensions... which I will try to convert from metric.

For a start, to substantiate my calling it tiny. 72.75" (185cm)drivers isn't that bad for a 4-8-4 -- several American classes had 73"-- but 213 lbs/sq.in. boiler pressure for a late 1940s design -- the prototype was built in 1949-- isn't impressive, and grate area of under 73 sq.ft. is smaller than any North American 4-8-4 except for the Temiskaming & Norther Ontario's. The weights, though, are the clearest indication that this design is "off the scale" of North American 4-8-4 types: weight per driving axle of 18 to 18.2 metric tonnes: a bit under 40,000 pounds. Total engine weight less than a large American Pacific type. ... Which, of course, is not meant as a criticism: these locomotives were designed for use on a railroad network with much lighter permissible axle loadings than on U.S. main lines, and they seem to have been quite successful!

I will try to put together a more detailed and systematic data table and post it here, but it will have some gaps I'd love others to fill. (Example: firebox dimensions.)
  by Allen Hazen
O.k.,starting my report on the data I have been able to find on the Russian P36 4-8-4, the largest class (251 built) of Northerns in the world.

There is a diagram online at
http://upload.wikimedia.org/wikipedia/c ... azmeri.jpg
(Note that the diagram doesn't show the skyline casing applied, as far as I know, to all units built. ... A "de-streamlined" P36 isn't as weird poking as a de-streamlined PRR T1!)

Dimensions from the diagram. I show in (parentheses) the metric measurements actually marked on the diagram; my conversions are slightly founded off.
These were primarily passenger locomotives,in size comparable to a light U.S.Pacific. After some measurements I show in {braces} the corresponding figure for the Light U.S.R.A. Pacific type.

Diameter: 78 3/4 inches (2 meters: not clear whether this is inside or outside, but if forced to guess I'd guess inside. Shown for course closest to the firebox,but the boiler barrel seems to be pretty cylindrical, not as coned as many U.S. locomotive boilers.) {U.S.R.A.: 74 5/8 inches inside first course, 86 inches outside largest course}
Tube length: 19 feet 8 inches (6 meters between what I take to be front and back tube sheets) {U.S.R.A.: 19 feet}
Combustion chamber: apparently none {U.S.R.A.: 23 1/2 inches}

Driving wheel diameter: 72 5/6 inches (1.85 meters) {U.S.R.A.: 73 inches}
Pilot truck wheel diameter: 35 1/2 inches (90 cm) {U.S.R.A.: 33 inches}
Trailing truck wheel diameter: diagram clearly mislabelled: perhaps a bit under 4 feet {U.S.R.A.: 43 inches}
Driving wheel base: 19 feet 10 inches
Engine shell base: 40 feet 10 inches

Running gear comment: The main drivers (second driving axle)are flangeless, which tome suggests that the lateral motion control arrangements were simpler than on late U.S. 4-8-4 types.

Weight on drivers: 159,570 pounds (individual axle weights shown, ranging from 18 to 18.2 metric tonnes) {U.S.R.A.: 162,000pounds)
Weight on front truck: 61,050 pounds (13.9 tonnes on first axle, 13.8 on second) {U.S.R.A.: 57,000pounds}
Weight on trailing truck: 72,952 pounds (16.3 tonnes on first, 16.8 on second axle) {U.S.R.A: 58,000 pounds}
Total engine weight: 293,573 pounds {U.S.R.A.: 277,000 pounds}
  by johnthefireman
I echo what Allen says in the OP: although South African railways are only 3' 6" gauge, some of the locomotives are huge.

According to Paxton and Bourne's "Locomotives of the South African Railways", the dimensions for the Class 25 4-8-4 are as follows:

Cylinder bore and stroke: 24" x 28"
Driving wheel diameter: 5' 0"
Boiler pressure: 225 lb / sq in
Tractive effort (75%) B.P.: 45,360
Weight engine (working order): 120 ton 9 cwt (25NC: 117 ton 9 cwt)
Weight tender (working order): 113 ton 18 cwt (25NC: 105 ton 11 cwt)
Total length over couplers: 107' 6 1/8" (25NC: 91' 6 9/16")
Grate area: 70 sq ft
Max axle load: 19 ton 6 cwt (25NC: 18 ton 14 cwt)

Can't find any dimensions for the Class 26, but it was a converted 25 so most major dimensions should be the same. Paxton and Bourne note that it had "35 per cent reduced coal consumption, 27 per cent reduced water consumption and 50 per cent increase in maximum drawbar horsepower" (p80).

David Wardale's "The Red Devil and Other Tales from the Age of Steam" has pages and pages of very detailed technical tables and graphs, but very little on Class 26 dimensions. The total engine weight of the Class 26 appears to have been 123 tons (p191).

The Class 26 has been preserved and is in Cape Town, although I believe most of the modifications have been removed. A number of Class 25NCs are still operational (I have fired a couple), and I think there is still one Class 25 (the original condenser version) which has not yet been scrapped lying around somewhere.

One of my favourite snippets about the Class 26 from Wardale's book is on p207: "One day no load was available for the outward trip to Witbank. On the 140m climb from Panpoort to Rayton I asked [driver] Vos to open up a bit and we took the grade (maximum 18%) at about 110 km h-1, only to be stopped by a red signal at Rayton station. Vos used the telephone by the signal to speak with the CTC operator and it transpired that we had zoomed past the axle counter of a hot box detector so fast that the counter had registered zero axles, and the Control wanted to know were we a ghost train or something?" I have frequently fired other locos (hauling loads) up Rayton Bank and we generally reckon it's a good day if we can keep the speed in double figures, let alone triple!
  by Allen Hazen
Thanks for posting that, John!
I've always liked the look of the 25/26 South African 4-8-4. To my American eye,they look very much like the NewYork Central's 6000-class "Niagara" 4-8-4: both were designed to be as big as could fit in their respective railway's clearance diagrams, with huge boilers, and as a result have very short stacks and no domes. (Is that right? The New York Central locomotives, I know, had dome less boilers: did the South African ones, or did they just have very low steam domes?)

One way for an American to appreciate how big they are is to compare them to a big U.S. 4-8-4scaled down: South African Railways track is 3'6" gauge: just a hair less than three-quarters of standard, 4'8",gauge. And the driver diameter on the 25 and 26 classes is 60": three quarters of the diameter of the largest drivers used on 4-8-4 in the U.S. So, compare them to a three-quarters-scale model of an ATSF 2900, the largest and heaviest U.S. 4-8-4. The 25/26 weight of 120 tons (I think that would be long tons of 2240 pounds) would come to about 268,000 pounds, or something over half the weight of a "full-scale" 2900: significantly heavier than the roughly 216,000 pounds of the 3/4 scale model (weight going with the cube of the linear dimensions). Or compare the cylinder dimensions: 24" bore and 28" stroke on the 25/26, as against 28"bore and 32" stroke on the full-sized 2900 and 21" by 24" on the 3/4 scale model!
  by johnthefireman
I've just consulted an expert and I'm told that the Class 25 is a "domeless" loco. Live steam is collected via collector pipes along the top of the boiler, in the same way as the GMAM, 15F, 23 and various others.
  by Allen Hazen
Thanks, John!
For comparison, the New York Central Niagara is described as having a pipe mounted high in the boiler with slots in it to collect steam. So the similar appearance of the 25 and the 6000 classes is the result of similar technology.
  by johnthefireman
Photo no 11 at http://www.friendsoftherail.com/phpBB2/ ... =86&t=8714 shows the steam collector pipe in a domeless Class 19D in South Africa. The caption reads:

'Large locomotives such as the 15F, 25 class, had bigger boilers and thus no room for a dome, so a number of "collector" pipes are fitted into the boiler at the highest internal point, to perform the work of the "dome"... Here we can see the collector pipes looking like rows of small trumpets.'

The 19D, incidentally, is not a "large" locomotive. Most of them did have domes with regular steam collection, but for some reason a few were built with domeless boilers and 2650, which survives in operational condition with Friends of the Rail in Pretoria, is one of them.
  by Triplex
If you're still looking
Very basic data, some in metric and some in imperial depending what the railroad itself used.
South Australia: two classes, both ~49000lb AL, drivers only 63" and 66"!
http://orion.math.iastate.edu/jdhsmith/ ... zgcprr.htm
China: <38000lb AL, ~69" drivers. The latter appear to have been standard for express passenger power in China.
Germany: ~44000lb AL, ~78.75" drivers. A rarity; a high-drivered non-US 4-8-4.
  by Allen Hazen
Thank you! I don't know about that site; it looks like a useful source of basic data.

Comments on the ones you mention:
--Of the two South Australian types, the earlier (heavier and lower-drivered)one was designed as a freight engine, at a time when South Australian Railways was deliberately trying to emulate NorthAmerican practice. The lighter 520 class was designed for service on lines with light rail: they had streamlining obviously inspired by the Pennsylvania T1!
--At least some of the Chinese 4-8-4 were, I think, built in Britain: not a country whose locomotive industry one associates with the type. (I have a vague memory that there may have been a project to bring one back to Britain for display in railway museum... but the memory is vague enough that you shouldn't trust me on this!)
--The French 242A1 (designed by André Chapelon) was also an express passenger type with high drivers.

... I have left this string alone for too long: I think I can get some information about some of these types, and should post it.
  by johnthefireman
As far as I can remember there is a Chinese loco in the National Railway Museum in York, UK. It's many years since I was there, but I recall it was standing next to a 9F, one of the largest locomotives ever to run in the Britain, and it completely dwarfed the 9F.
  by Allen Hazen
(Johnthefireman--Thanks: York is the obvious place to go to see a Chinese 4-8-4! As for dwarfing... the British loading gauge is very small, so British locomotives are likely to be overshadowed by any built for a less restrictive clearance envelope.)

I have managed to find a bit of data about South Australia's 4-8-4 locomotives: two classes, built in the 1920s and the 1940s, with proposals for more that were still-born because of dieselization. A bit of history in this post, some numbers to follow. Main source: "500: the 4-8-2 and 4-8-4 locomotives of the South Australian Railways," published by the South Australian Division of the Australian Railway Historical Society, Adelaide, first edition 1969, second (the one I have) 1979.


Compared to the major North American systems that had fleets of 4-8-4, the South Australian Railway was quite a small operation. (This shouldn't be surprising: even after WW II, Australia had a total population of only about 8 million, spread over a land area not much smaller than the 48 contiguous states of the U.S., and South Australia is, in population, one of the smaller states.) It might compare with the Boston and Maine: both have main lines radiating from the state capital (which has extensive commuter service operated, in the 1950s and later, with diesel cars). It was a mixed-gauge system, with a good deal of narrow (3'6") gauge in the north, but the main lines out of Adelaide, for which the 4-8-4 were built, were built to 5'3" gauge: a track gauge shared with South Australia's larger (in population) neighbour to the east, Victoria. Much of the track was built with very light rail, but the main line from Adelaide to the Victorian border has a long stretch of 2% grade climbing out of Adelaide. The "big" power of the early 20th C was a class of light 4-6-0; by the 1920s the "Overlander" (overnight passenger train from Adelaide to Melbourne in Victoria)was often triple-headed.

In the 1920s an American railroader, W.A. Webb, was appointed as the head of South Australian Railways, and undertook to modernize the system along American-inspired lines. A key plank of his program was a "Big Engine" policy, and in 1926 several classes (4-6-2, 2-8-2 and-- our topic-- 4-8-2 types) much larger than previous South Australian locomotives were introduced: engines large and heavy enough that they could only operate on the most heavily built main lines.

The 4-8-2, ten locomotives numbered 500-509, are of obviously North American inspiration (though the designs were drawn up by an Australian engineer, S.A.R.'s motive power head F.J. Shea), and (after bids were received from a number of Australian, British, North American, and European builders) were built by Armstrong-Whitworthin Newcastle-on-Tyne. The design called for American-style cast-steel bar frames, which British locomotive builders of the time were not able to provide: the frames were subcontracted to Baldwin. (Next time somebody tells you of the problems Boeing has had coordinating all their international sub-contractors for the 787, point out to them that the practice is not new!)

The new locomotives had been designed for operation on 80-pound rail, and within weeks reports of broke rails started to come in. Apparently most of the problem was with 50 or 60 pound rail (on sidings? in yards?): Webb denied that there had been problems with 80 pound rail... but also admitted that curves on parts of the main line were to be re-laid with 100 pound rail.

As a 4-8-2, the 500 had a tractive effort of 51,000 pounds (200 lb/sq.in boiler pressure, 26"x28" cylinders, 63" drivers, t.e. calculated at 85% boiler pressure). Given the 2% grades, more was felt desirable and, starting in 1929, the locomotives were retrofitted with trailing truck boosters: the new trailing trucks had two axles,making the locomotives (which were assigned the class "500B" after conversion) the first Australian 4-8-4. (All ten were ultimately converted, though-- perhaps because of the Depression? -- two were left as 4-8-2 until 1936).

Numbers coming soon.
  by Allen Hazen
The 500/500B locomotives had some post-delivery refinements to the boiler (improved exhaust, etc), but the main boiler dimensions don't seem to have been changed in converting them from 4-8-2 to 4-8-4. So:

A: Pressure, 200 pounds/square inch
B: diameter, 6' 2.5" behind smoke-box, 7' at firebox. (Sorry: source doesn't say if this is outside or inside.)
C: length over tube plates 21' 6"
D: 177 2.25 inch tubes, 36 5.5" flues
E: Grate area, 66.6 square feet
F: heating surface: 3253 sq. ft. tubes and flues, 395 sq. ft. firebox and arch tubes, 835 sq ft superheater
G: combustion chamber perhaps (judging by eye from drawing) 42"

This is not a BIG locomotive by North American standards. For comparison, the corresponding numbers for the boiler on a U.S.R.A. Light Mikado are:
A: 200
B: 6' 4.625", 7' 6"
C: 19'
D: 216, 40
E: 66.7
F: 3497, 280, 882
G: 24"

Weights and wheelbase to come.
  by Allen Hazen
(Correction to my reply to Triplex, 23 April: I said that the 500 class were designed for freight work: they were actually intended from the start to be dual-service, with the crack Melbourne-Adelaide express being one of their standard assignments.)

Since this string is about 4-8-4 comparisons, I will only give the dimensions and weights for these locomotives after their conversion to 4-8-4.

--4' 5.25", front coupler to first axle of pilot truck
--7' wheelbase of pilot truck
--5' rear axle of pilot truck to first driving axle
--5' 8" between adjacent driving axles
----(so, driving wheelbase of 17')
--6' 11" rear driving axle to first axle of trailing truck
--4' 6" wheelbase of trailing truck
----(so 40' 5" engine wheelbase)
--11' 2.5" rear axle of trailing truck to first tender axle
--These locomotives were equipped with four-axle tenders; the total engine and tender wheelbase was 74' 1.5"; total length over couplers 84' 2".

Wheel diameters:
--Pilot truck, 33"
--Driving, 63"
---Trailing truck, first axle, 36"
---Trailing truck, rear axle, 42"

Weights (in working order):
--On pilot truck, 54,656 pounds
--On drivers:
---First driving axle, 48,832 pounds
---Second (main) driving axle, 49,616 pounds
---Third driving axle, 49,168 pounds
---Fourth driving axle, 48,832 pounds
----Total on drivers, 196,448 pounds
--Trailing truck:
---First axle, 30,912 pounds
---Second axle, 40,768 pounds
----Total on trailing truck, 71,680 pounds
--Total engine weight, 322,784 pounds

Comment 1: Total engine weight is comparable to the USRA heavy 2-8-2 (320,000 pounds) or light 4-8-2 (327,000 pounds). Weight on drivers comparable to USRA heavy 4-6-2 (197,000 pounds). The tractive effort (without booster) of 51,000 pounds gives a Factor of Adhesion of just over 3.85.
Comment 2: Conversion from 4-8-2 to 4-8-4 added 19,860 pounds to total engine weight. The original, single-axle, trailing truck had 48,860 pounds on it; the springing was adjusted so some weight was transferred away from the drivers: the original Factor of Adhesion had been just under 3.9.
  by sllanso
Hi, Allen:
I've been compiling Locobase for 20 years and have over 13,000 entries. Half of them cover North American locomotives (which can be seen at Wes Barris's http://www.steamlocomotive.com website) and the other half---don't. Within the non-North American half, I've recorded data for several 4-8-4s that ran in countries we don't normally think of. Here's the Locobase commentary for the Spanish RENFE Confederacions.

Data from http://www.renfe.es/wf/ix.exe?IBIF_ex=PFHIR5A2&TO=176 (last accessed 17 May 2006).

Pere Comas, whose Paleontolgia Vaporosa posts on the family tree of Spanish 4-8-0s are referenced in Locobase 3382, refers to this "Confederacion" class as "Velocepedus Largtijus" in signfication of their power-at-speed qualities and the long-boilered profile painted dark green that gave rise to the nickname "Lagarto" (lizard).

Ten locomotives supplied by the Barcelona works of Maquinista Terrestre Y Maritima. These drew heavily on the 2-10-2 design that entered service in the mid-1940s and using the same boiler and firebox. The 4-8-4s burned diesel oil.

Equipped with the Walschaert-driven Lenz poppet valve gear. TIA water-treatment system, a feedwater heater, double Kylchap blast pipe. The cab was mounted on springs, presumably to reduce crew fatigue.

Pulled 750-ton trains with ease at speeds up to 68 mph. (Hollingsworth -- 1982 -- notes that trials showed a top speed of 84 mph and cylinder horsepower of 4,000. He notes a more typical service performance of 600 tons up 1% at 35 mph sustained.)"
Here's the data portion of Locobase 1130 (many of the fields are presented in both English and metric measurements:
unit of measure label
1130 Locobase record number
38854 Date first created
41096 Last updated
5'6" Gauge
38085 Whyte description
Tender - simple Locomotive type
Spain Country of operation
RENFE Railroad
242-2001 Name of record
MTM Builder
45926 lb Tractive effort
20831.70796 kg Tractive effort
35120 lb
2001-2010 Road numbers
1956 Year first built
10 Number built
10 Number in class
2 Number of HP cylinders
25.2 inches HP cylinder diameter
640 mm HP cylinder diameter
27.95 inches HP cylinder stroke
710 mm HP cylinder stroke
227.7 psi Boiler pressure
15.7 bar Boiler pressure
74.8 inches Driver diameter
1900 mm Driver diameter
lb Booster tractive effort
Number of LP cylinders
0 inches LP cylinder diameter
0 mm LP cylinder diameter
0 inches LP cylinder stroke
0 mm LP cylinder stroke
16.13463082 cu ft
0 cu ft
16.13463082 cu ft
1.109126984 ratio ratio of cylinder stroke to diameter
ratio ratio of LP/HP cylinder volumes
3162 sq ft Evaporative heating surface
293.72 sq m Evaporative heating surface
1125 sq ft Superheater surface area
104.55 sq m Superheater surface area
4287 sq ft Combined heating surface area
398.27 sq m Combined heating surface area
0.26 pct Pct of SHS to CHS
801.3213902 ratio CHS/(TE*Driver diam)
195.9759746 ratio ratio of HS/HP cylinder volume
2.676207513 ratio Cylinder stroke to driver diam
57.05 sq ft Grate area
5.3 sq m Grate area
55.42506573 ratio EHS/grate area
75.14460999 ratio CHS/grate area
281.48 sq ft Firebox heating surface
26.15 sq m Firebox heating surface
0.089019608 pct FireboxHS/EHS
60214.98335 ratio Grate area/(TE*Driver diam)
4.933917616 ratio Firebox HS/Grate area
78.74 inches Smallest boiler diameter
2000 mm Smallest boiler diameter
0 inches Combustion chamber length
0 mm Combustion chamber length
20.75 ft Tube length over tubesheets
6.33 metres Tube length over tubesheets
389.2976504 ratio Tube length/cross-section
0.193026107 pct tube cross-section area/grate area
150 Number of tubes
2.165 inches Diameter of tubes
55 mm Diameter of tubes
48 Number of flues
5.236 inches Diameter of flues
133 mm Diameter of flues
0.651772754 pct Pct of EHS made up of flue surface area
2880.52 sq ft EHS-Firebox HS when both are given
3129.450005 sq ft Tube HS given tube count, length, diam
-0.072980098 pct Diff
18.21 ft Driving wheelbase
5.55 metres Driving wheelbase
282191 lb Weight, engine, empty
128000 kg Weight, engine, empty
314158 lb Weight, engine, loaded
142500 kg Weight, engine, loaded
0.547367885 pct Adhesion weight/engine weight
48502 lb Max axle loading
22000 kg Max axle loading
3.744284283 ratio Adhesion weight/Tractive effort
19.49995918 metric tons Est minimum average load per axle
5506.713409 lb Engine weight/Grate area
72 lb minimum rail weight/yard
0 lb Weight, tender, empty
0 kg Weight, tender, empty
149914 lb Weight, tender, loaded
464072 lb Weight, engine & tender, loaded
464072 lb
210500 kg Weight, engine & tender, loaded
68000 kg Weight, tender, loaded
7128 US gallons Water capacity
27 cu m Water capacity
3567 tons or US gal Fuel (tons or US gallons)
13.5 metric tons Fuel (tons or US gallons)
171960 lb Weight on drivers
78000 kg Weight on drivers
43.31 ft Engine wheelbase
13.2 metres Engine wheelbase
0.420457169 pct Pct of adhesion wheelbase/engine wheelbase
75.23 ft Engine & tender wheelbase
22.93 lb Engine & tender wheelbase
metres Engine & tender wheelbase
9443.163097 lb Weight/foot of adhesion wheelbase
7253.705842 lb Weight/foot of engine wheelbase
Lenz Valve gear
Schmidt Type A Superheater type

The attachment wizard doesn't allow txt extensions, so I'm not sure how to send the Excel table I created of the other four entries. If worse comes to worse, I could go off-Forum and email them to you directly.

Steve Llanso

If you'd like the data and comments for the others, please let me know and I'll send them along.