Pennsylvania 2-8-8-0 "Consolidation Mallet" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class HC1s (Locobase 309)

Data from "Pennsylvania's New Simple Mallet Type Locomotive," Railway and Locomotive Engineering, July 1919, pp. 193-194; "Simple Mallet Locomotive Pennsylvania RR," Railway Review, Volume 68, No 3 (19 July 1919), pp. 81-88; "2-8-8-0 Simple 'Mallet' Locomotive, Pennsylvania Railroad", Locomotive Magazine, Volume XXVI [26] (15 May 1920), pp. 109-110 and 15 July 1920, pp. 146-148 ; and Alvin F Staufer, Pennsy Power Steam and Electric Locomotives of the Pennsylvania Railroad, 1900 1957 (Alvin F Staufer, 1962), text by Bert Pennypacker, research by Martin Flattley, p.19.. Juniata works number was 3633 in June 1919

One-of-a-kind articulated for the Pennsy, who preferred to be the non-Standard Railroad of the World when it came to that kind of engine. All in all, it seems to have been the most successful of all of the Pennsylvania's home-grown articulateds. It certainly didn't lack for innovation.

Like other Pennsylvania engines, too, it burned its fuel in a Belpaire firebox. (See Locobase 32 for a comment on the unique design of Pennsy's Belpaire firebox.) Live steam entered all four cylinders through 12" (305 mm) piston valves. These were set for a maximum cutoff of 50% and a long 2" (50.8 mm) lap. The Railway Review added that an auxiliary port opened in advance of the main valve to "offset the rather slow building up of pressure in the cylinders at the beginning of the stroke." The Pennsylvania rated the engine's tractive effort at 135,600 lb (61,507 kg/603.2 kN).

The HC-1's boiler had 19-ft-long tubes and a combustion chamber measuring 12' 5 1/2" (3.797 m). This front section was a continuation of the 14' x 8' (4.27 x 2.44 m) firebox proper and was separated from it by a low steel firewall that constricted the flame to an 18 sq ft (1.67 sq m) area. Thus the crown sheet measured 26' 5 1/2" (8.07 m) overall. From trackside, its length could easily be seen as the characteristic crease in the Belpaire boiler's wrapper that sloped upward as it extended forward.

The total length of the boiler came to 53' 9 1/2" (16.40 m), possibly the longest ever mounted, of which 26 ft (7.92 m) included the crown sheet. So long were the boiler and crown sheet that special pipes were led up out of the wrapper sheet at the front of the combustion chamber and continued back to gauge cocks to ensure that the crew would know the proper water level.

The oddness of the layout extended to the tube and flue combination. The superheater had three vertical headers and two superheater steam headers, each unit, says the R&LE, "...being connected to from two to five units, each unit leading and returning to or from one of the larger flues." The center header contained 568 1 1/8" (29 mm) tubes

A multiple blast-pipe arrangement consisted of the two main exhaust pipes (11"/279 mm for the rear engine set, 9 1/2"/241 mm) for the lead engine), which met in the smokebox. There, each pipe was topped by a bifurcated tube that ended in two 4 1/2"(114 mm) pipes. The center of each of these four smaller nozzles was set at a corner of a 15 3/4" (400 mm) square array. These in turn directed their blast up through 15" (381 mm) diameter "lift pipes" So, as the Railway Review remarked, while the stack appeared circular from the outside, the casing actually surrounded the four pipes, whose draft was aided by a circle of 20 1/4" (6.35 mm) drilled in the inside of the top of the stack to create a further smoke-lifting action.

This engine is reported to have run well as a pusher in Allegheny Mountain service until it was retired in 1929. Bert Pennypacker, in Staufer's Pennsy Power, offered a more nuanced view. It quickly became apparent, Pennypacker wrote, that its "drawbar heave-ho was simply too much for many freight cars of the day with older styles of draft gear." So "she" was relegated to pusher work.

Pennypacker contended "she wasn't too successful. The steam distribution was figured wrong plus [sic] high cylinder maintenance cost. This added up to a costly operation which the railroad didn't like." Had the locomotive been successful, Pennypacker adds, the Pennsy might gone with a fleet of articulateds, but the I-1s 2-10-0 (5153, 15921, and 67) were powerful two-cylinder locomotives that readily handled the tonnage. "All of this explains why," he concluded,"598 I-1s engines were built and four-cylinder articulateds forgotten."

Principal Dimensions by Steve Llanso of Middle Run Media

Locobase ID309
RailroadPennsylvania (PRR)
Number in Class1
Road Numbers3700
Number Built1
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)34.25 / 10.44
Engine Wheelbase (ft / m)54.70 / 16.67
Ratio of driving wheelbase to overall engine wheelbase 0.63
Overall Wheelbase (engine & tender) (ft / m)97.31 / 29.66
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)540,000 / 244,940
Engine Weight (lbs / kg)575,000 / 260,816
Tender Loaded Weight (lbs / kg)219,000 / 99,337
Total Engine and Tender Weight (lbs / kg)794,000 / 360,153
Tender Water Capacity (gals / ML)12,900 / 48.86
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)13.90 / 13
Minimum weight of rail (calculated) (lb/yd / kg/m)113 / 56.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)62 / 1575
Boiler Pressure (psi / kPa)205 / 14.10
High Pressure Cylinders (dia x stroke) (in / mm)30.5" x 32" / 775x813 (4)
Tractive Effort (lbs / kg)167,325 / 75897.43
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.23
Heating Ability
Tubes (number - dia) (in / mm)137 - 2.25" / 57
Flues (number - dia) (in / mm)284 - 3.25" / 83
Flue/Tube length (ft / m)19 / 5.79
Firebox Area (sq ft / m2)531 / 49.33
Grate Area (sq ft / m2)112 / 10.41
Evaporative Heating Surface (sq ft / m2)6656 / 618.59
Superheating Surface (sq ft / m2)3136 / 291.45
Combined Heating Surface (sq ft / m2)9792 / 910.04
Evaporative Heating Surface/Cylinder Volume122.99
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation22,960
Same as above plus superheater percentage30,307
Same as above but substitute firebox area for grate area143,689
Power L114,692
Power MT479.86

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Wes Barris