Madrid, Zaragoza & Alicante 4-6-2 Locomotives in Spain


Class Details by Steve Llanso of Sweat House Media

Class 231-2011 (Locobase 3241)

Data from "Locomotives of American Design for Use in Spain," Railway Age, Volume 71, No. 4 (23 July 1921), pp. 167-168. See also Via Libre diagram book, p. 23. Works numbers were 61772-61786 in April 1920.

Handsome, moderately scaled Pacifics for the MZA to satisfy service requirements for the express passenger and mail runs from Madrid to Barcelona, Santa Cruz, Alicante, and Cordoba. The service requirements were:

Trailing load Grade Speed Curve radius

280 1.5% 31.5 ( 50 km/h) 1,312 (400 metres)

310 1.0% 37.3 ( 60 km/h) 1,312

400 level 62.1 (100 km/h) 2,297 (700 metres)

Via Libre's account of the class said that the MZA approached Alco with a request that they build more of the four-cylinder compounds already in service on the MZA. Alco declined and for "unknown" ("desconocemos") reasons accepted a "type so classically American that neither the trademark MZA cab nor the stack's visor and lid could disfigure it." (Locobase's translation). These Pacifics were the first in Europe to use "only two cylinders where in such powerful locomotives it was considered necessary to divide the motion."

The boiler achieved 350 deg of superheat. Firebox heating surface included 13 sq ft (1.21 sq m) of arch tubes. Accuracy in RA's reporting apparently didn't extend to its specifications table. The journal reported the heating surface area as 1,461 sq ft (135.7 sq m), a figure well short even of the tube surface area (1,851 sq ft/172.0 sq m) as measured from the inside. When the latter figure is used, evaporative heating surface area works out to 2,007 sq ft (186.5 sq m) and this is the figure used in the diagram offered by Via Libre..

Railway Age claimed that although lighter than the older Twelve-wheelers, "they are satisfactorily handling the same loads, run easily at the fastest speeds allowed and if delayed are usually able to make up lost time. The arrangement of the trucks and the disposition of the suspension permits running at high speed without trouble from journal heating."

April 1921's figures show each engine averaging 3,510 miles while burning 71.5 lb of coal per train mile, the latter comparing "very favorably with that of the most economical locomotives on the road."

OS Nock (RWC IV, pl 165) shows a tidy American design and he adds that except for one engine (912) destroyed in the Civil War, the class ran on through most of the 1960s.


Class 231-4021 (Locobase 3363)

Data from [], the web site of the Spanish National Railway. See also Pere Comas, Breve Historia de la Traccion Vapor en MZA, Trensim TS10H002, Julio de 2011., p.54.

Comas pointed out that these four-cylinder compounds always operated on secondary services and never acquired a nickname despite their relatively advanced design. They noted that RENFE in particular showed little enthusiasm for compounds and relegated them to duties that were beneath their abilities.

Principal Dimensions by Steve Llanso of Sweat House Media

Class231-2011231-4021
Locobase ID3241 3363
RailroadMadrid, Zaragoza & Alicante (MZA)Madrid, Zaragoza & Alicante (MZA)
CountrySpainSpain
Whyte4-6-24-6-2
Number in Class154
Road Numbers901-915877-880/231-4021 a 231-4024
Gauge5'6"5'6"
Number Built154
BuilderAlco-BrooksMaffei
Year19211913
Valve GearWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)12.01 / 3.6612.47 / 3.80
Engine Wheelbase (ft / m)32.34 / 9.8636.42 / 11.10
Ratio of driving wheelbase to overall engine wheelbase 0.37 0.34
Overall Wheelbase (engine & tender) (ft / m)59.19 / 18.0459.71 / 18.20
Axle Loading (Maximum Weight per Axle) (lbs / kg)35,274 / 16,00035,274 / 16,000
Weight on Drivers (lbs / kg)105,822 / 48,000105,822 / 48,000
Engine Weight (lbs / kg)188,495 / 85,500188,495 / 85,500
Tender Loaded Weight (lbs / kg)105,160 / 47,700104,279 / 47,300
Total Engine and Tender Weight (lbs / kg)293,655 / 133,200292,774 / 132,800
Tender Water Capacity (gals / ML)5280 / 205201 / 19.70
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT) 5.50 / 55 / 5
Minimum weight of rail (calculated) (lb/yd / kg/m)59 / 29.5059 / 29.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)68.90 / 175068.90 / 1750
Boiler Pressure (psi / kPa)169.70 / 11.70232.10 / 16
High Pressure Cylinders (dia x stroke) (in / mm)22.99" x 25.98" / 585x66015.75" x 25.59" / 400x650
Low Pressure Cylinders (dia x stroke) (in / mm)24.41" x 25.59" / 620x650
Tractive Effort (lbs / kg)28,747 / 13039.4425,667 / 11642.37
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.68 4.12
Heating Ability
Tubes (number - dia) (in / mm)148 - 1.969" / 50193 - 1.969" / 50
Flues (number - dia) (in / mm)28 - 5.394" / 13724 - 5.236" / 133
Flue/Tube length (ft / m)19 / 5.8015.91 / 4.85
Firebox Area (sq ft / m2)148.54 / 13.80157.69 / 14.65
Grate Area (sq ft / m2)44.02 / 4.0944.13 / 4.10
Evaporative Heating Surface (sq ft / m2)2156 / 200.302104 / 195.45
Superheating Surface (sq ft / m2)705 / 65.50576 / 53.53
Combined Heating Surface (sq ft / m2)2861 / 265.802680 / 248.98
Evaporative Heating Surface/Cylinder Volume172.73364.62
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation747010,243
Same as above plus superheater percentage933812,394
Same as above but substitute firebox area for grate area31,50944,286
Power L114,43115,530
Power MT901.94970.62

All material Copyright © SteamLocomotive.com
Wes Barris