Baltimore & Ohio 4-8-2 "Mountain" Locomotives of the USA

In 1925, the Baltimore & Ohio Railroad built its first "Mountain" locomotive (road number 5500) using the boiler from number 6009, a Baldwin built Class S 2-10-2. A year later. the B&O built another (road number 5501) using the boiler from number 6030. These two locomotives were designated Class T and had 30 x 30 cylinders, 74" drivers, and a 220 psi boiler pressure which resulted in a tractive effort of 68,200 pounds. They weighed 400,000 lbs and worked on the west end of the Cumberland Division pulling passenger trains until retired in 1953.

In 1930, George Emerson, the General Superintendent of Motive Power & Equipment wanted to prove his theory that a water-tube firebox was practical. He had the B&O order two "Mountain" type locomotives from the Baldwin Locomotive Works, one (Class T-1, road number 5510) equipped with a water-tube firebox and the other (Class T-2, road number 5550) with a conventional type firebox. These two locomotives were identical except for their fireboxes and had 27.5 x 30 cylinders, 74" drivers, a 250 lbs boiler pressure and exerted 65,000 lbs of tractive effort. Number 5510 weighed 384,000 lbs and number 5550 weighed 1,000 lbs more. Emerson wanted to operate the two locomotives in similar service and then compare operating and maintenance costs. This experiment was never completed and the two "Mountains" were used until the early 1950s.

In the early 1940s, the B&O decided to build "Mountain" type locomotives to help with the increase in traffic caused by the war effort. From 1942 to 1948 it built forty of them (Class T-3, road numbers 5555 through 5594) in its Mt. Clare Shops in Baltimore, MD. These locomotives were built to the same general specifications which included 27 x 32 cylinders, 70" drivers, a boiler pressure of 230 psi, a tractive effort of 65,100 lbs and a weight of 375,000 pounds. There were some variations in the features of these locomotives as shown in the chart below. The Class T-3s were retired in 1960.

The B&O bought thirteen 4-8-2s from the Boston & Maine. They were given road numbers 5650 through 5662 and were designated as Class T-4 and were used until 1958.

There are no surviving B&O "Mountains". The Class Ts (numbers 5500 & 5501) were scrapped in 1953. Class T-1 number 5510 was scrapped in 1951 and Class T-2 number 5550 was scrapped in 1952. Some of the Class T-3s and T-4s were scrapped in the early 1950s. In 1957, all of the remaining T-3s and T-4s were renumbered in the 700 series. The T-4s were retired in 1958 and the T-3s lasted a little longer, but by 1960 all of the B&O "Mountain" had been scrapped.

Roster by Richard Duley

ClassQty.Road NumbersYear BuiltNotes

T-335555-55571942Vanderbilt tenders with 15,000 gallons of water and 26 tons of coal.

T-3a155641943Same as T-3 except it had roller bearings on all axles.

T-3b35565-55671943Same as T-3 except it had large square tank tender with 20,000 gallons of water and 25 tons of coal. (no roller bearings)

T-3c75585-55911947Roller bearings on pony, tailing and tender axles. Same tender as T-3b.

Class Details by Steve Llanso of Sweat House Media

Class T (Locobase 196)

Data from tables in 1930 Locomotive Cyclopedia and B&O to 1954 Assorted Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

Firebox heating surface included 42 sq ft (3.9 sq m) of arch tubes.

Two engines built by the B&O using class S 2-10-2 boilers (Locobase 1036) on a shorter wheelbase. The 5500 had 29" (737 mm) diameter cylinders while the 5501 had the square dimensions shown in the specs. They also had 14" (356 mm) piston valves instead of the 16" (406 mm) valves feeding the 2-10-2s.

Although 74" drivers promised a good dual-role engine, the B&O did not follow up on this design, possibly because the boiler was in fact too long for a four-axle driving layout. Both retired in 1953.

Class T-1 (Locobase 3097)

Data from B&O Staufer Locomotive Diagrams (Medina, Ohio: Alvin Stauffer), p. 94 supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Works number was 61569 in November 1930.

One of two Mountains built by Baldwin in 1930 to test the Emerson watertube firebox alongside a conventional stayed firebox. In the Emerson, a 40" diameter drum ran along the centerline over the grate and from front sheet to back head. Headers at the top and bottom of the firebox were connected by two rows (190 tubes total) of 2 1/2" diameter water tubes. The top header was joined to the drum by 13 4"-diameter nipples on each side.

The value of the Emerson firebox was held to be the much greater heating surface it offered to the fire. From 474 sq ft of evaporative surface, including syphons, in the stayed firebox, the surface expanded 82% to 866 sq ft in the Emerson (including the 83 sq ft of arch tubes).

Unfortunately for such designs, the system was prey to vibration, insufficient insulation, maintenance headaches. Moreover, it didn't after all offer much of an advantage. The T-1 and the articulated KK-1 were the only watertube engines supplied to the B&O.

Class T-2 (Locobase 3098)

Data from B&O Staufer Locomotive Diagrams (Medina, Ohio: Alvin Stauffer), p. 95 supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Works number was 61554 in November 1930.

This was the conventional, stayed firebox variant of the Mountain tested by the B&O against the T-1 (Locobase 3097), which had a watertube firebox. As part of the firebox heating surface, the T-2 had 18 sq ft (1.65 sq m) of arch tubes and 95 sq ft (8.8 sq m) of thermic syphons.

Like the T-1, the T-2 soldiered on solo until 1951.

Class T-3b/T-3c (Locobase 193)

Data from B&O to 1954 Assorted locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

Similar T-3b class numbered from 5565-5594. 40 locomotives built by the B&O from 1942 to 1948 using boilers from retired 4-6-2 and 2-8-2 engines. The frame was cast steel with integral cylinders. The shops fitted several different fireboxes to engines in this class. One was a 363 sq ft (33.7 sq m) unit that included 35 sq ft (3.25 sq m) of arch tubes and 14 sq ft (1.3 sq m) in a single thermic syphon. The second added the syphon and 49.9 sq ft (4.65 sq m) of circulators to the basic 314 sq ft (29.17 sq m) of grate surface. The third added one more circulator to bring the total to the 388 sq ft shown in the specs. A fourth, apparently mounted only on certain T-3Bs, added 72 sq ft (6.7 sq m) of circulators to the grate area and achieved the same firebox heating surface area.

Last T-3 retired in 1960.

Specifications by Steve Llanso of Sweat House Media
Locobase ID196 3097 3098 193
RailroadBaltimore & Ohio (B&O)Baltimore & Ohio (B&O)Baltimore & Ohio (B&O)Baltimore & Ohio (B&O)
Number in Class21140
Road Numbers5500-5501551055505555-5594
Number Built21140
Valve GearBakerWalschaertWalschaertBaker
Locomotive Length and Weight
Driver Wheelbase19.25'19.25'19.25'18.25'
Engine Wheelbase41.33'44.59'44.59'40.58'
Ratio of driving wheelbase to overall engine wheebase 0.47 0.43 0.43 0.45
Overall Wheelbase (engine & tender)89'91.16'88.10'
Axle Loading (Maximum Weight per Axle)69300 lbs65900 lbs65000 lbs
Weight on Drivers275000 lbs260000 lbs260000 lbs255000 lbs
Engine Weight400000 lbs384000 lbs385000 lbs375000 lbs
Tender Light Weight259300 lbs273000 lbs273000 lbs265000 lbs
Total Engine and Tender Weight659300 lbs657000 lbs658000 lbs640000 lbs
Tender Water Capacity15100 gals18000 gals18000 gals20000 gals
Tender Fuel Capacity (oil/coal)18 tons20 tons20 tons25 tons
Minimum weight of rail (calculated)115 lb/yard108 lb/yard108 lb/yard106 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter74"74"74"70"
Boiler Pressure210 psi250 psi250 psi230 psi
Cylinders (dia x stroke)30" x 30"27.5" x 30"27.5" x 30"27" x 32"
Tractive Effort65128 lbs65150 lbs65150 lbs65152 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.22 3.99 3.99 3.91
Heating Ability
Firebox Area383 sq. ft866 sq. ft474 sq. ft388 sq. ft
Grate Area89.17 sq. ft92 sq. ft92.30 sq. ft70 sq. ft
Evaporative Heating Surface5593 sq. ft5403 sq. ft5489 sq. ft3950 sq. ft
Superheating Surface1305 sq. ft1340 sq. ft1365 sq. ft1071 sq. ft
Combined Heating Surface6898 sq. ft6743 sq. ft6854 sq. ft5021 sq. ft
Evaporative Heating Surface/Cylinder Volume227.88261.98266.15186.27
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation18726230002307516100
Same as above plus superheater percentage22284276002769019481
Same as above but substitute firebox area for grate area95712259800142200107980
Power L120317325823011619650
Power MT651.511105.091021.45679.54



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