Norfolk & Western 2-6-6-2 "Mallet Mogul" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class Z1/Z1a - Alco (Locobase 1467)

Data from N&W 12-1929 Locomotive Diagram and N&W 10-1929 Locomotive Class books supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also Brotherhood of Locomotive Engineers and the Brotherhood of Locomotive Firement and Enginemen, Evolution of Increased Power and Tonnage, Quotations from Railway Technical Experts and Publications, 1913, pp 15-16.

Locobase split what was one record into three to provide for differences in boiler size and changes in the basic design of this large class of Mallets over a long career. This entry gives data for the Richmond and Schenectady locomotives. The first to entered service were fifteen Richmond Z1s in April-May 1912 and were the only ones equipped with Walschaert outside radial valve gear. These were delivered a boiler pressed to 200 psi, a setting that was very shortly raised to 225 psi as shown. Firebox heating surface initially included 134 sq ft in a combustion chamber and 22 sq ft of arch tubes.

From September 1912 to August 1913, Richmond added 65 Z1a that had as their principal difference the Baker-Pilliod valve gear.

The BLE/BLFE compilation (intended to bolster their cases for higher pay rates) quotes a detailed Railway Age Gazette report from its 9 May 1913 issue (pp. 1025-1026) about the reasons behind the purchase and the nature of their use: "In ordering this equipment, it was the purpose of the Norfolk & Western officials, not so much to dispense with the pusher service, as to increase the maximum train load over the division."

RAG gave an overview of two operating divisions and how they used the 2-6-6-2s: "On the Pocahontas division, between Eckman, W. Va., and Bluefield, five 0-8-8-0 type, five 2-8-8-2 type, and fifteen of the new 2-6-6-2 type Mallets are being operated in both head end and pusher service.

"On the Radford division, between Bluefield and Roanoke, Va., five of the new 2-6-6-2 type Mallets are being operated in road service. This division is 105 miles long and includes a forty-mile grade of 0.4 per cent and a ten-mile grade of 1.0 per cent." The Z1/Z1a helpers increased train tonnage from 2,800 to 4,000 tons up the ten-mile grade.

Twenty others went to work as road engines between Roanoke. Va., and Crewe, a distance of 130 miles. According to RAG "Because of especially favorable terminal as well as road facilities, these Mallets are doing their best work on this division."

After outlining the limitations of the double-headed 4-8-0 motive power pulling 3,500 tons, the RAG described the contrast afforded by 2-6-6-2 operation: "At present, starting out from Roanoke with a 5.000-ton train, one of these Mallets is in the lead, double-headed by a 4-8-0 type locomotive. These two engines pull the train from Roanoke to Bonsack, a distance of 9 miles, made up of broken grades. At Bonsack another of the Mallets is put behind the train and pushes it to Blue Ridge, a distance of 6 miles. From Bonsack to Blue Ridge there is a ruling grade of 1.2 per cent. At Blue Ridge the pusher cuts out and returns to Bonsack light. From Blue Ridge the two engines in the lead haul the train to Phoebe, a distance of 56 miles from Blue Ridge. This 56 miles is made up of broken grades, but includes a 0.5 per cent grade 8 miles long. At Phoebe the leading 4-8-0 type engine is cut off and waits for a westbound empty train helping as a double-header back to Roanoke. From Phoebe, therefore, the one Mallet or through engine hauls the train to Crewe, a distance of 59 miles of broken grade, with the exception of the 16 miles from Farmville to Burkeville. This 16 miles is made up of a continuous grade of 0.45 per cent and a 4-8-0 type engine is used as a pusher.'

Clearly, main-line steam freight operations were involved (an additional reason to quote this passage at some length), but one with tangible results: "This means that on the Radford division train loads have been increased 79 per cent, and on the Roanoke division 43 per cent. Fifty-seven locomotives have been supplanted by these forty Mallets, and a reduction of 25 per cent has been effected in the number of freight trains operated over the divisions."

Baldwin secured the next contracts in 1914 (Locobase 14233), then Alco's Schenectady works completed the N&W stud of 2-6-6-2s with 30 in January-March 1916, 20 in January-February 1917, and 20 more in July-August 1918. The Z1 would also heavily influence the United States Railroad Administration design of its light articulated 2-6-6-2.

All were later modified and updated; see Locobase 14232.

Class Z1a - BLW (Locobase 14233)

Data from N&W 12-1929 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also DeGolyer, Vol 50, pp.263+ . Baldwin works numbers were 41483-41486, 41508-41511 in June 1914; 41520-41529, 41531-41536, 41545-41549, 41556-41558 in July; and 41569-41576 in August.

Locobase split what was one record into three to provide for differences in boiler size and changes in the basic design of this large class of Mallets over a long career. This entry covers the 40 Eddystone products that had a smaller boiler than the much more numerous Alco batches described in Locobase 1467.

Like the early Richmonds, this group entered service with a boiler pressed to 200 psi; this setting was soon raised to 225 psi as shown. The firebox heating surface was essentially similar to the Alcos and included 134 sq ft (12.45 sq m) in a combustion chamber and 28.8 sq ft (2.68 sq m) in arch tubes. The difference in the tube count between these Baldwin's and the 243 in the Alcos appears to originate in the requirement to omit 19 of the flues at the bottom of the boiler "and provide additional bracing on account of leaving these flues out."

All 40 were delivered with mechanical stokers: the first 25 had Street Automatic Stokers, the last 15 used Hanna stokers supplied free by the railway.

The Baldwin specs concerning staybolt indicates the size and complexity of such boilers. In the first twenty engines, 728 Tate Flexible staybolls of Rome Superior iron, spaced not more than 4" center to center and pneumatically driven, were required. The next ten had 720 American Flexible Belt Company flexible staybolts of American Iron & Steel Company's AAA iron in the breaking zone only, and in the last ten engines, Baldwin provided "complete installation" 1,826 similar bolts. Locobase suspects the N&W was comparing the three different installations for quality of installation and ease of maintenance.

See Locobase 14232 for the much later rebuilds that included all Z1/Z1as.

Class Z1a - updated (Locobase 14232)

Data from N&W 3-1955 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Locobase split what was one record into three to provide for differences in boiler size and changes in the basic design of this large class of Mallets over a long career. Locobase 1467 describes the 150 Alco originals while 14233 gives the details of the 40 Baldwins.

Seventy-four Z1b (17 Baldwin, 57 Alco) were converted by the N&W in the late 1920s-early 1930s by substituting 14" piston valves for the slide valves originally supplied for their LP cylinders and by installing Worthington feedwater heaters. These had their adhesion weight increase to 376,581 lb and total engine weight to 440,000 lb.

The later diagrams (first dated 1942) showed that the N&W reduced the count of small tubes from the 243 of the original Alcos and the 224 of the Baldwins. Locobase suspects that the deduction came from the bottom of the boiler.

So modified, the class served the big coal road until the 1950s with the last retiring by

Class Z2 (Locobase 7824)

Data from N&W 3-1955 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

EL King, writing in Drury (1993), says that the N & W rebuilt one of its Z1 compound articulateds (Locobase 1467) as a simple-expansion locomotive, but it was not a success. The boiler was simply too small to supply 4 high-pressure cylinders with steam. Therefore, 1399 remained an only engine until its retirement 6 years later.

Principal Dimensions by Steve Llanso of Sweat House Media
ClassZ1/Z1a - AlcoZ1a - BLWZ1a - updatedZ2
Locobase ID1467 14,233 14,232 7824
RailroadNorfolk & Western (N&W)Norfolk & Western (N&W)Norfolk & Western (N&W)Norfolk & Western (N&W)
Number in Class14040151
Road Numbers1300-1379, 1420-14891380-14191300-14901339
Number Built140401
BuilderAlcoBaldwinN&WNorfolk & Western
Valve GearBaker or WalschaertBakerBakerBaker
Locomotive Length and Weight
Driver Wheelbase (ft / m)10 / 3.0510 / 3.0510 / 3.0510 / 3.05
Engine Wheelbase (ft / m)48.83 / 14.8848.83 / 14.8848.83 / 14.8848.83 / 14.88
Ratio of driving wheelbase to overall engine wheebase 0.20 0.20 0.20 0.20
Overall Wheelbase (engine & tender) (ft / m)88.60 / 27.0179.21 / 24.1487.46 / 26.6694.56 / 28.82
Axle Loading (Maximum Weight per Axle) (lbs / kg)62,600
Weight on Drivers (lbs / kg)354,500 / 160,799339,000 / 153,768354,500 / 160,799377,825 / 171,379
Engine Weight (lbs / kg)427,000 / 193,684408,000 / 185,066427,000 / 193,684441,000 / 200,034
Tender Loaded Weight (lbs / kg)167,500 / 75,977167,500 / 75,977212,000 / 96,162286,530 / 129,968
Total Engine and Tender Weight (lbs / kg)594,500 / 269,661575,500 / 261,043639,000 / 289,846727,530 / 330,002
Tender Water Capacity (gals / ML)9000 / 34.099000 / 34.0920,000 / 75.7616,000 / 60.61
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)14 / 12.7014 / 12.7016 / 14.5023 / 20.90
Minimum weight of rail (calculated) (lb/yd / kg/m)98 / 4994 / 4798 / 49105 / 52.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)57 / 144856 / 142257 / 144856.50 / 1435
Boiler Pressure (psi / kPa)225 / 15.50200 / 13.80225 / 15.50225 / 15.50
High Pressure Cylinders (dia x stroke) (in / mm)22" x 32" / 559x81322" x 32" / 559x81322" x 32" / 559x81322" x 32" / 559x813 (4)
Low Pressure Cylinders (dia x stroke) (in / mm)35" x 32" / 889x81335" x 32" / 889x81335" x 32" / 889x813
Tractive Effort (lbs / kg)74,498 / 33791.7667,403 / 30573.5274,498 / 33791.76104,852 / 47560.12
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.76 5.03 4.76 3.60
Heating Ability
Firebox Area (sq ft / m2)369 / 34.28374.80 / 34.82391 / 36.32391 / 36.34
Grate Area (sq ft / m2)72.20 / 6.7172.20 / 6.7172.20 / 6.7172.20 / 6.71
Evaporative Heating Surface (sq ft / m2)5048 / 468.974742 / 440.544629 / 430.044629 / 430.20
Superheating Surface (sq ft / m2)971 / 90.211022 / 94.95971 / 90.21971 / 90.24
Combined Heating Surface (sq ft / m2)6019 / 559.185764 / 535.495600 / 520.255600 / 520.44
Evaporative Heating Surface/Cylinder Volume358.55336.81328.79164.39
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation16,24514,44016,24516,245
Same as above plus superheater percentage18,84417,03919,00719,007
Same as above but substitute firebox area for grate area96,30988,453102,931102,931
Power L193778284919211,530
Power MT349.89323.24342.99403.67

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