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Mallets with more than six coupled axles[Inhalt]
Bavarian Gt 2x4/4
German Reichsbahn class 96
Germany | 1913
25 produced
No. 5773 from the second batch
No. 5773 from the second batch
Hermann Merker Verlag

Around 1910 it had become clear that the existing locomotives were no longer able to pull heavy freight trains over the Bavarian ramps at sufficient speed. Despite two pusher locomotives, trains could often hardly go more than 20 km/h, which could no longer be described as economical. Thus, Maffei developed a heavy tank locomotive in Mallet construction with two eight-coupled bogies

Side view of the second batch
Side view of the second batch
Die Lokomotive, December 1925

The resulting locomotive was the most powerful tank locomotive in Europe at the time. Since no carrying axles were necessary due to the low speeds on the ramps, the entire mass could be used as adhesive mass. It was able to pull 670 tonnes at 18 km/h alone on a gradient of two percent. At 2.5 percent it could still tow 540 tonnes, which was 100 tonnes more than two examples of the E 1.

Side view and schematic drawing of the first construction lot
Side view and schematic drawing of the first construction lot
Die Lokomotive, June 1914

A total of 15 of this locomotives were built in 1913 and 1914, and they proved themselves immediately. Both with a single pusher loco behind a freight train or with only one Gt 2x4/4 each as leading and pusher loco, significant increases in the speeds at the ramps were now made possible. After strong competition emerged with the Prussian T 20 in an 2-10-2T wheel arrangement, another ten Gt 2x4/4 were produced in 1922 and 1923. These were revised in many aspects to be even more powerful.

In 1925 and 1926 all engines were modified in order to bring both series to a more uniform and somewhat stronger level. The supplies and the total weight were increased, which now made more adhesive weight available. In addition, seven wheel sets instead of two were now sanded, which was a great advantage under difficult traction conditions. The Reichsbahn took over all 25 engines and classified them as class 96. After the end of World War II, 18 remained, two of which went to the Soviet occupation zone and the rest to the West. The Bundesbahn retired them as a minor class by 1948 and they remained in service with the Reichsbahn until 1954.

Variant1913 variant1922 variant1925 rebuild
General
Built1913-19141922-19231925-1926
ManufacturerMaffei
Axle config0-8-8-0T (Angus (Mallet)) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length57 ft 6 15/16 in58 ft 2 13/16 in58 ft 0 7/8 in
Wheelbase40 ft 0 5/16 in
Rigid wheelbase14 ft 9 3/16 in
Empty weight214,950 lbs224,430 lbs234,792 lbs
Service weight270,066 lbs281,089 lbs291,671 lbs
Adhesive weight270,066 lbs281,089 lbs291,671 lbs
Axle load33,951 lbs36,156 lbs36,707 lbs
Water capacity2,906 us gal3,249 us gal2,906 us gal
Fuel capacity8,818 lbs (coal)11,023 lbs (coal)9,921 lbs (coal)
Boiler
Grate area45.7 sq ft
Firebox area158.8 sq ft157.7 sq ft
Tube heating area2,154 sq ft2,359.4 sq ft2,157.4 sq ft
Evaporative heating area2,312.7 sq ft2,517.1 sq ft2,315.1 sq ft
Superheater area596.2 sq ft621.1 sq ft703.6 sq ft
Total heating area2,908.9 sq ft3,138.2 sq ft3,018.7 sq ft
Variant1913 variant1922 variant1925 rebuild
Power Plant
Driver diameter47.9 in
Boiler pressure218 psi
Expansion typecompound
Cylindersfour, HP: 20 1/2 x 25 3/16 in
and LP: 31 1/2 x 25 3/16 in
four, HP: 23 5/8 x 25 3/16 in
and LP: 31 1/2 x 25 3/16 in
Power
Power sourcesteam
Indicated power1,448 hp (1,080 kW)1,609 hp (1,200 kW)
Estimated power1,475 hp (1,100 kW)
Optimal speed16 mph18 mph14 mph
Top speed31 mph
Starting effort57,363 lbf69,530 lbf
with start valve68,836 lbf83,436 lbf
Calculated Values
steam locomotive
freight
Mallet
last changed: 01/2022
Duluth, Missabe & Northern classes M, M-1 and M-2
United States | 1910
12 produced
M-1 No. 209
M-1 No. 209

In 1910, the DM&N initially received eight heavy Mallets of the 2-8-8-2 wheel arrangement, which they designated as class M and which largely corresponded to the class AB No. 600 of the Virginian. The intended area of operation was the ten miles from the docks in Duluth to Proctor at a gradient of 2.2 percent. Here the locomotive alone was to be able to push 55 empty ore wagons uphill at 12 mph

They were still operated with saturated steam, but had a second feedwater heater between the high and low pressure cylinders in addition to the regular one. By default, no stoker was installed, instead two firemen were used. While the 55 cars were a great challenge for the two firemen on the incline, locomotives with a retrofitted stoker could transport up to 85 empty ore cars. In the years 1916 and 1917, two more locomotives each followed, which were designated as class M-1 and M-2. These had a superheater from the factory and were five feet shorter overall.

Of the eight class M locomotives, seven were fitted with a superheater in 1925 and all those that did not yet have a stoker were retrofitted with one. The last locomotive, number 207, was built in 1930 in a total rebuild. In the completely new boiler, the superheater had a significantly larger share, resulting in a heating surface that was almost 60 percent larger overall. The cylinders were now of the same size without compound working. In the same year, the four M-1 and M-2 received a similar boiler with the larger superheater and four simple cylinders, which made them the M-2-S class.

VariantMM superheatedM-1, M-2M-2-S
General
Built191019251916-19171930
ManufacturerBaldwinDM&NBaldwinDM&N)
Axle config2-8-8-2 (Mikado Mallet) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase58 ft 2 in55 ft 9 in55 ft 4 in
Rigid wheelbase15 ft
Total wheelbase87 ft83 ft 6 1/2 in83 ft 10 in
Service weight448,100 lbs436,000 lbs470,200 lbs494,450 lbs
Adhesive weight406,600 lbs392,200 lbs415,200 lbs421,100 lbs
Total weight620,000 lbs607,900 lbs647,000 lbs689,650 lbs
Axle load50,825 lbs49,025 lbs51,900 lbs52,640 lbs
Water capacity9,000 us gal
Fuel capacity32,000 lbs (coal)42,000 lbs (coal)
Boiler
Grate area84 sq ft
Firebox area255 sq ft340 sq ft379 sq ft417 sq ft
Tube heating area6,635 sq ft3,782 sq ft5,045 sq ft5,024 sq ft
Evaporative heating area6,890 sq ft4,122 sq ft5,424 sq ft5,441 sq ft
Superheater area931 sq ft1,168 sq ft2,480 sq ft
Total heating area6,890 sq ft5,053 sq ft6,592 sq ft7,921 sq ft
VariantMM superheatedM-1, M-2M-2-S
Power Plant
Driver diameter57 in
Boiler pressure200 psi
Expansion typecompoundsimple
Cylindersfour, HP: 26 x 32 in
and LP: 40 x 32 in
four, 24 x 32 in
Power
Power sourcesteam
Estimated power3,200 hp (2,386 kW)3,400 hp (2,535 kW)3,700 hp (2,759 kW)3,900 hp (2,908 kW)
Optimal speed22 mph24 mph26 mph23 mph
Starting effort90,709 lbf109,945 lbf
with start valve108,851 lbf
Calculated Values
steam locomotive
freight
Mallet
Articulated
last changed: 07/2023
Erie class L-1
United States | 1907
3 produced
Locomotive Magazine, September 1907

In the early years of the twentieth century, Mallet locomotives served only as an articulated solution for narrow-gauge railways. The L-1 of the Erie Railroad of 1907 was one of the first to show that very large freight locomotives could also be built with the Mallet principle. At the time it was commissioned, it was the largest and most powerful locomotive in the world. Since it was only intended as a pusher locomotive and did not have to reach high speeds, there was no need for leading or trailing axles. Thus, all eight axles were available as adhesive weight. The wheel arrangement was soon called “Angus”.

No. 2601
No. 2601

A Wooten firebox with a grate area of 100 square feet was used to maximize the energy yield from low-grade coal. In order to still ensure a good view for the engineer, the L-1 was built as a camelback engine and thus had the cab above the rearmost axle of the front bogie. It was the only camelback Mallet ever built.

Schematic drawing
Schematic drawing
Railway and Locomotive Engineering, September 1907

Only three examples were built, which were used on the Delaware and Susquehanna divisions to push trains up a 1.3 percent incline. They were rebuilt to a more conventional form in 1921. The cab was moved to the rear and two carrying axles were added, whereby they now had the wheel arrangement 2-8-8-2.

General
Built1907
ManufacturerALCO
Axle config0-8-8-0 (Angus (Mallet)) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length84 ft 9 3/4 in
Wheelbase39 ft 2 in
Rigid wheelbase14 ft 3 in
Total wheelbase70 ft 5 in
Service weight410,000 lbs
Adhesive weight410,000 lbs
Total weight577,700 lbs
Axle load54,100 lbs
Water capacity8,500 us gal
Fuel capacity32,000 lbs (coal)
Boiler
Grate area100 sq ft
Firebox area348.3 sq ft
Tube heating area4,965.7 sq ft
Evaporative heating area5,314 sq ft
Total heating area5,314 sq ft
Power Plant
Driver diameter51 in
Boiler pressure215 psi
Expansion typecompound
Cylindersfour, HP: 25 x 28 in
and LP: 39 x 28 in
Power
Power sourcesteam
Estimated power3,000 hp (2,237 kW)
Optimal speed22 mph
Starting effort88,890 lbf
with start valve106,668 lbf
Calculated Values
steam locomotive
freight
Mallet
camelback
last changed: 06/2022
View model on YouTube
Erie class P-1
United States | 1914
3 produced
Ron Ziel, „American Locomotives 1858 to 1949”

On mountain routes such as Susquehanna Hill, the Erie Railroad had the problem that the 3,500 to 5,500 ton trains, each pulled by a Consolidation or Mikado locomotive in the lowlands, could only be brought over the incline with difficulty. Two helper locomotives were often necessary, although some mallets were already being used. With the support of George R. Henderson of Baldwin, a triplex locomotive was built, which had three four-axle engine groups. Only the prototype was built in 1914, christened “Matt H. Shay” after a well-known railroad employee.

The six cylinders were all of the same dimensions to give compound action with two high pressure and four low pressure cylinders. The cylinders in the middle acted as high-pressure cylinders, with the exhaust steam from the right-hand cylinder being fed into the cylinders of the front bogie and the exhaust steam from the left into the cylinders on the rear bogie. Only the exhaust from the front low-pressure cylinders went into the smokebox, while the rear operated a feedwater heater in the tender.

During operation, it was quickly noticed that the boiler was not producing enough steam to reach significant speeds. Although the grate on the following two 1916 engines was increased from 90 to 122 square feet, they too failed to produce sufficient steam. Even the large firebox with brick arch and combustion chamber could not improve this situation. As a result, the locomotives were only used as pushers, where average speeds were barely over 10 mph

No. 700 “Matt H. Shay” in May 1915 in Susquehanna, Pennsylvania
No. 700 “Matt H. Shay” in May 1915 in Susquehanna, Pennsylvania
John B. Allen

The powered tender also proved problematic in practical use. It offered a smaller capacity than conventional tenders of the same size because the engine took up space and increased the empty mass. When the supplies were used up, the adhesive weight of the tender also dropped so much that it quickly began to slip. Since the other chassis groups were now also suddenly subject to greater loads, they quickly lost grip. Thus, their number stagnated at three and the Class XA of the Virginian remained the only other triplex locomotive that was built. A quadruple locomotive already planned by Henderson was not implemented. The three examples of the P-1 were retired in 1929, 1931 and 1933.

General
Built1914, 1916
ManufacturerBaldwin
Axle config2-8-8-8-2 (Triplex) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase71 ft 6 in
Rigid wheelbase16 ft 6 in
Total wheelbase91 ft
Service weight853,050 lbs
Adhesive weight761,600 lbs
Axle load70,100 lbs
Water capacity11,600 us gal
Fuel capacity32,000 lbs (coal)
Boiler
Grate area121.5 sq ft
Firebox area468 sq ft
Tube heating area6,418 sq ft
Evaporative heating area6,886 sq ft
Superheater area1,584 sq ft
Total heating area8,470 sq ft
Power Plant
Driver diameter63 in
Boiler pressure210 psi
Expansion typecompound
Cylinderssix, HP: 36 x 32 in
and LP: 36 x 32 in
Power
Power sourcesteam
Estimated power2,000 hp (1,491 kW)
Optimal speed5 mph
Starting effort235,008 lbf
with start valve282,010 lbf
Calculated Values
steam locomotive
freight
triplex
last changed: 09/2022
Great Northern (US) class L-3
later classes M-1 and M-2
United States | 1909
35 produced
flickr/Twin Ports Rail History

In order to prevent individual chassis groups from slipping on slow freight trains, the Great Northern ordered a Mallet with unequal axle distribution. The front group consisted of a leading axle and three driving axles, while the rear group consisted of four driving axles. After ten locomotives from 1909, another 25 followed, which had a significantly larger tube heating area. Under the new scheme, they were designated class M-1.

They were converted to simple expansion to save complexity from 1926 and were designated class M-2. The rear cylinders remained slightly larger in order to be able to convert enough power for the additional driving axle. The existing feedwater heater was also removed. The locomotives had a choppy running that made speeds over 25 mph (40 km/h) difficult to run. 22 were scrapped from 1929 and their parts used for new O-7 class Mikados, while the remaining 13 partially survived until 1954.

Variantfirst seriessecond seriesrebuilt M-2
General
Built190919101926-1928
ManufacturerBaldwinGreat Northern
Axle config2-6-8-0 (Mallet) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase43 ft 11 in
Rigid wheelbase12 ft 6 in15 ft
Total wheelbase76 ft 2 1/2 in85 ft 5 in
Service weight368,700 lbs403,000 lbs
Adhesive weight350,000 lbs384,000 lbs
Total weight522,800 lbs583,000 lbs
Axle load51,400 lbs50,000 lbs56,000 lbs
Water capacity8,000 us gal10,000 us gal
Fuel capacity26,000 lbs (coal)4,500 us gal (oil)
Boiler
Grate area78 sq ft
Firebox area225 sq ft258 sq ft
Tube heating area3,059 sq ft3,525 sq ft4,982 sq ft
Evaporative heating area3,284 sq ft3,750 sq ft5,240 sq ft
Superheater area480 sq ft579 sq ft1,490 sq ft
Total heating area3,764 sq ft4,329 sq ft6,730 sq ft
Variantfirst seriessecond seriesrebuilt M-2
Power Plant
Driver diameter55 in
Boiler pressure200 psi210 psi
Expansion typecompoundsimple
Cylindersfour, HP: 23 x 32 in
and LP: 35 x 32 in
four, front: 22 x 32 in
rear: 23 1/2 x 32 in
Power
Power sourcesteam
Estimated power2,350 hp (1,752 kW)2,500 hp (1,864 kW)2,900 hp (2,163 kW)
Optimal speed20 mph22 mph18 mph
Starting effort73,085 lbf107,620 lbf
with start valve87,702 lbf
Calculated Values
steam locomotive
freight
Mallet
Articulated
last changed: 03/2023
Norfolk & Western classes Y4a, Y5 and Y6
United States | 1930
97 produced
Y6a no. 2154 in 1956 at Shaffers Crossing, Colorado
Y6a no. 2154 in 1956 at Shaffers Crossing, Colorado
Bob Krone

The last generation in their series of 2-8-8-2 wheel arrangement Mallets, begun in 1910, was built by Norfolk & Western from 1930. While most other North American railroads had long since abandoned real Mallets and introduced ones with simple steam expansion instead the last series still had a compound engine. They were all made in the Roanoke workshops of Norfolk & Western and it all started with the Y4a as a development of the Y4 with an enlarged grate and significantly higher boiler pressure. Some optimizations were made to the internal piping that increased efficiency.

A young boy admires Y6 no. 2127 in May 1955
A young boy admires Y6 no. 2127 in May 1955
collection Taylor Rush

The first eight Y4a left the factory in 1930 and still had forged frames. On the ten Y5s from 1931, the frames were cast in one piece. The Y4as were also fitted with the new frames in 1940 and 1941. Also in 1940, 35 Y6s followed, in which the cylinders were now manufactured together with the frame as a cast part and had roller bearings on all axles. These were followed by another 15 Y6as, delivered in 1942.

Y6a no. 2162 (front) and Y6b no. 2200 (rear) in January 1958 at Grundy, Virginia
Y6a no. 2162 (front) and Y6b no. 2200 (rear) in January 1958 at Grundy, Virginia
collection Taylor Rush

Between 1948 and 1952, 30 examples of the Y6b followed, which would become the most modern Mallet locomotives in North America. They featured a larger firebox and a special mechanism that allowed them to run at all speeds with single steam expansion, increasing tractive effort at the expense of efficiency. The front bogie with the low-pressure cylinders was weighed down with several tons of lead to increase the adhesive weight. The diameter of the coupled wheels was one inch larger, and these were also retrofitted to the predecessors. In the last few years of service, the locomotives were equipped with technical aids that increased the starting tractive effort to almost 170,000 pounds or 755 kN.

All in all, the locomotives are considered to be the most powerful, commercially successful steam locomotives ever. Some earlier prototypes could muster even higher starting tractive effort, but the boiler no longer provided sufficient steam as the speed increased. However, the Y4a to Y6b could also haul heavy trains at up to 50 mph and at 25 mph with 13,500 tons on the hook achieved a drawbar power of 5,500 hp. Although this was surpassed by the Big Boy, this was designed for higher speeds and therefore had a lower starting tractive effort than the locomotives described here with single steam expansion. These large Mallets were retired by 1960 and today only Y6a number 2156 survives. It belongs to the Saint Louis Museum of Transportation and is not roadworthy.

VariantY4a, Y5Y6, Y6aY6b
General
Built1930-19311940, 19421948-1952
ManufacturerRoanoke
Axle config2-8-8-2 (Mikado Mallet) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length114 ft 10 1/2 in
Wheelbase58 ft
Rigid wheelbase102 ft 9 in103 ft 10 in103 ft 8 1/4 in
Total wheelbase15 ft 9 in
Service weight582,900 lbs582,899 lbs611,520 lbs
Adhesive weight522,850 lbs548,501 lbs
Total weight961,500 lbs961,499 lbs990,119 lbs
Water capacity22,000 us gal
Fuel capacity54,400 lbs (coal)
Boiler
Grate area106.2 sq ft
Firebox area430 sq ft555 sq ft
Tube heating area5,394 sq ft5,219 sq ft4,360 sq ft
Evaporative heating area5,824 sq ft5,649 sq ft4,915 sq ft
Superheater area1,582 sq ft1,775 sq ft1,478 sq ft
Total heating area7,406 sq ft7,424 sq ft6,393 sq ft
VariantY4a, Y5Y6, Y6aY6b
Power Plant
Driver diameter57 in58 in
Boiler pressure300 psi
Expansion typecompound
Cylindersfour, HP: 25 x 32 in
and LP: 39 x 32 in
Power
Power sourcesteam
Estimated power6,000 hp (4,474 kW)6,200 hp (4,623 kW)
Optimal speed30 mph32 mph
Starting effort126,831 lbf124,644 lbf
with start valve152,197 lbf149,573 lbf
Calculated Values
steam locomotive
freight
Mallet
last changed: 07/2022
Northern Pacific class Z-3
United States | 1913
21 produced
ALCO / collection Taylor Rush

In 1913, the Northern Pacific had its first superheated Mallets made for the operation of heavy, slow freight trains over the Cascades and in the Rocky Mountains. The ten locomotives came from ALCO in Schenectady and had the wheel arrangement 2-8-8-2. Four were coal-fired and destined for the Rocky Mountains, while the other six were oil-fired for the Seattle Division. A total of eleven more from ALCO Brooks followed in 1917 and 1920.

With cylinders measuring 26 and 40 inches in diameter, respectively, they developed more than 85,000 pounds of pulling power. However, these had such a high steam consumption that the highest power was already available at 10.6 mph. In operation, it had been shown that they could pull almost 30 percent more load as pilot compared to a class Z-1 locomotive while consuming the same amount of coal. In the cascades they pulled up to 2,400 short tons alone over most of the run, but were helped by another Mallet on the steeper sections with up to 2.2 percent.

Variant1913 variant1917 variant
General
Built19131917, 1920
ManufacturerALCO
Axle config2-8-8-2 (Mikado Mallet) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase55 ft 2 in
Rigid wheelbase15 ft
Total wheelbase83 ft 6 1/4 in
Service weight456,000 lbs483,000 lbs
Adhesive weight399,500 lbs419,500 lbs
Total weight649,200 lbs688,600 lbs
Axle load53,700 lbs56,900 lbs
Water capacity10,000 us gal
Fuel capacity3,500 us gal (oil)32,000 lbs (coal)
Boiler
Grate area84.2 sq ft84.3 sq ft
Firebox area368 sq ft373.6 sq ft
Tube heating area5,129 sq ft5,123.4 sq ft
Evaporative heating area5,497 sq ft
Superheater area1,225 sq ft1,305 sq ft
Total heating area6,722 sq ft6,802 sq ft
Variant1913 variant1917 variant
Power Plant
Driver diameter57 in
Boiler pressure200 psi
Expansion typecompound
Cylindersfour, HP: 26 x 30 in
and LP: 40 x 30 in
Power
Power sourcesteam
Estimated power3,200 hp (2,386 kW)
Optimal speed24 mph
Starting effort85,039 lbf
with start valve102,047 lbf
Calculated Values
steam locomotive
freight
Mallet
last changed: 03/2023
Santa Fe class 3000
United States | 1911
10 produced
The first vehicle built, No. 3000
The first vehicle built, No. 3000
Detroit Publishing Co.

In order to explore the extreme limits of the Mallet principle, the Atchison, Topeka & Santa Fe developed the class 3000 in 1911 with the wheel arrangement 2-10-10-2 and a weight of 309 short tons. The goal was to be able to pull 2,000-ton trains with just one locomotive over gradients of 1.2 percent in Arizona. In order to speed up development and production, the running gear for each of the ten examples was taken from two standard Baldwin 2-10-2 locomotives and combined into one locomotive. The existing cylinders were used as rear high-pressure cylinders and Baldwin had larger low-pressure cylinders made for the front bogie. A special development was the flat six-axle tender with a rounded rear section, which was called “Turtleback” and was intended to provide better rear visibility. It contained oil for firing.

A normal boiler of the same length as the class 3000 could not be realized and therefore only the rear half was used as a classic boiler barrel with combustion chamber and smoke tubes. The front half was used as a feedwater heatersuperheater and reheater for the exhaust steam from the high-pressure cylinders. All in all, it was found that this boiler did not generate enough steam for the powerful engine and therefore sustained speeds of only 10 to 15 mph were possible.

In view of the low speeds, the locomotives were not used directly to pull heavy freight trains, but had to push other trains uphill. There they were mainly found in California on Cajon Pass and in the famous Tehachapi Loop. Nevertheless, the demolition of the first locomotives back to simple 2-10-2 locomotives began as early as 1915. When the last ones were dismantled in 1918, they had earned the nickname “magnificent failures”. Only the new design of the tender was considered successful and used in later Santa Fe locomotives.

General
Built1911-1912
ManufacturerBaldwin
Axle config2-10-10-2 (Mallet) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length122 ft 0 3/16 in
Wheelbase66 ft 5 in
Rigid wheelbase19 ft 5 1/2 in
Total wheelbase108 ft 10 in
Service weight616,000 lbs
Adhesive weight550,000 lbs
Total weight882,450 lbs
Water capacity12,000 us gal
Fuel capacity4,000 us gal (oil)
Boiler
Grate area82 sq ft
Firebox area284.5 sq ft
Tube heating area3,637 sq ft
Evaporative heating area3,921.5 sq ft
Superheater area2,381 sq ft
Total heating area6,302.5 sq ft
Power Plant
Driver diameter57 in
Boiler pressure225 psi
Expansion typecompound
Cylindersfour, HP: 28 x 32 in
and LP: 38 x 32 in
Power
Power sourcesteam
Estimated power2,000 hp (1,491 kW)
Optimal speed12 mph
Starting effort109,113 lbf
with start valve130,936 lbf
Calculated Values
steam locomotive
freight
Mallet
last changed: 03/2022
View on YouTube
Southern Pacific class MC-1
United States | 1909
2 produced
collection Taylor Rush

In 1909, the Southern Pacific ordered two class MC-1 Mallets from Baldwin in the 2-8-8-2 wheel arrangement, which were the heaviest locomotives in the world at the time. They were intended to haul ever heavier freight trains across the Sierra Nevada. In the test runs with the two machines, the aim was to gain experience for later series production.

Since the Schmidt superheater had not yet fully established itself, a different design was chosen for the very large boiler. First there was a feedwater heater with an area of 1,221 sq ft. The high-pressure cylinders were then operated with saturated steam, which was passed through a 655 sq ft reheater before being passed on to the low-pressure cylinders.

During operation, it quickly became clear that the smoke produced by these powerful locomotives in the many tunnels posed a serious danger to the crews. Thus, the following classes from the MC-2, as well as the AC series, were built as Cab Forward. The two MC-1s were also converted into MC-2s in 1923. In 1931 they were converted to simple expansion and scrapped in 1947 and 1948 respectively.

General
Built1909
ManufacturerBaldwin
Axle config2-8-8-2 (Mikado Mallet) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase56 ft 7 in
Rigid wheelbase15 ft
Total wheelbase83 ft 6 in
Service weight425,900 lbs
Adhesive weight394,145 lbs
Total weight606,100 lbs
Axle load50,260 lbs
Water capacity10,800 us gal
Fuel capacity3,420 us gal (oil)
Boiler
Grate area68.4 sq ft
Firebox area232 sq ft
Tube heating area4,941 sq ft
Evaporative heating area5,173 sq ft
Superheater area655 sq ft
Total heating area5,828 sq ft
Power Plant
Driver diameter57 in
Boiler pressure200 psi
Expansion typecompound
Cylindersfour, HP: 26 x 30 in
and LP: 40 x 30 in
Power
Power sourcesteam
Estimated power3,000 hp (2,237 kW)
Optimal speed22 mph
Starting effort85,039 lbf
with start valve102,047 lbf
Calculated Values
steam locomotive
freight
Mallet
last changed: 03/2023
Southern Pacific classes MC-2, MC-4 and MC-6 and AC-1 to AC-3
United States | 1909
47 produced
AC-3 No. 4043 which had previously been an MC-6
AC-3 No. 4043 which had previously been an MC-6
collection Taylor Rush

The first locomotives that Southern Pacific had built as cab forwards were the MC-2. They were similar to the MC-1, but were reversed with the cab at the front. In order to be able to transport the oil into the firebox, the tender had an overpressure of five psi. The exhaust steam from the high-pressure cylinders was reheated before being passed into the low-pressure cylinders. In 1909 a total of 15 of this class were built and the two MC-1 were rebuilt into the MC-2.

A further twelve MC-4 followed in 1911, which were virtually identical to the MC-2. In contrast, the 20 MC-6 that were delivered in 1912 and 1913 already had a superheater. To increase the speed of the locomotives, they were rebuilt between 1930 and 1937 with four identical cylinders, a larger superheater and a Worthington feedwater heater. The MC-2, MC-4 and MC-6 became the AC-1, AC-2 and AC-3, which now stood for “Articulated Consolidation”. They were used in the Second World War for freight trains, but also for passenger trains and troop transports, and were retired between 1946 and 1949.

VariantMC-2, MC-4MC-6rebuilt AC-1 to AC-3
General
Built1909, 191119121927-1930
ManufacturerBaldwinSacramento
Axle config2-8-8-2 (Mikado Mallet) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length loco67 ft 7 in
Wheelbase56 ft 7 in
Rigid wheelbase15 ft
Total wheelbase90 ft 4 in
Service weight433,600 lbs435,800 lbs481,200 lbs
Adhesive weight398,000 lbs400,700 lbs440,800 lbs
Total weight613,000 lbs620,460 lbs
Axle load51,200 lbs
Water capacity10,000 us gal
Fuel capacity3,200 us gal (oil)
Boiler
Grate area68.4 sq ft
Firebox area240 sq ft362 sq ft
Tube heating area4,701 sq ft3,937 sq ft4,514 sq ft
Evaporative heating area4,941 sq ft4,177 sq ft4,876 sq ft
Superheater area839 sq ft2,150 sq ft
Total heating area4,941 sq ft5,016 sq ft7,026 sq ft
VariantMC-2, MC-4MC-6rebuilt AC-1 to AC-3
Power Plant
Driver diameter57 in
Boiler pressure200 psi210 psi
Expansion typecompoundsimple
Cylindersfour, HP: 26 x 30 in
and LP: 40 x 30 in
four, 22 x 30 in
Power
Power sourcesteam
Estimated power2,700 hp (2,013 kW)3,000 hp (2,237 kW)3,500 hp (2,610 kW)
Optimal speed20 mph22 mph25 mph
Starting effort85,039 lbf90,941 lbf
with start valve102,047 lbf
Calculated Values
steam locomotive
freight
Mallet
Articulated
cab forward
last changed: 11/2023
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