Data from "New Consolidation Mineral Engine, Somerset & Dorset Joint Ry", Locomotive Magazine, Volume XX [20], No 260 (15 April 1914), p. ; "1 D Heiádampf-Güterzuglokomotive der Sommerset-Dorset-Verbindungsbahn mit Rauchr"hrenüberhitzer Patent Schmidt. In: Die Lokomotive. 14. Jg., Nr. 1, Januar 1917, S. 4-7 (onb.ac.at) at [], last accessed 10 August 2025; and "Mineral Engines for the Somerset & Dorset Joint Ry", Locomotive Magazine, Volume XX [20], No 261 (15 May 1914), p. . (Thanks to Peter Christener for his 2 August 2025 email filling in the blank on the boiler's tube length and for supplying the link to the Die Lokomotive report.)
Powerful Consolidation designed by Henry Fowler and first put into service just before World War I. Although smaller in boiler size and lighter on the drivers than most British 2-8-0s, this engine generated a higher tractive effort. It had a relatively large Belpaire firebox area and good-sized superheater.
The [] link from the West Somerset Railway's link gives a detailed history of this class. "The locomotives were the first on the S&D to have outside cylinders and Walschaerts valve gear," says the history. "The cylinders were inclined at 1 in 12, to clear the platform edges. ...The locomotives were amongst the most powerful in the country at the time."
A later (1925) batch -- 86-90 -- had larger boilers fitted with 146 1 3/4" small tubes and 21 5 1/8" flues and and show a Belpaire firebox with 190.7 sq ft of direct heating surface. The grate area did not change.
| Principal Dimensions by Steve Llanso of Middle Run Media | |
|---|---|
| Class | 7F/ G9AS |
| Locobase ID | 3658 |
| Railroad | Somerset & Dorset Joint |
| Country | Great Britain |
| Whyte | 2-8-0 |
| Number in Class | 6 |
| Road Numbers | 80-85 /13800-13805 |
| Gauge | Std |
| Number Built | 6 |
| Builder | Derby |
| Year | 1914 |
| Valve Gear | Walschaert |
| Locomotive Length and Weight | |
| Driver Wheelbase (ft / m) | 17.49 / 5.33 |
| Engine Wheelbase (ft / m) | 25.75 / 7.85 |
| Ratio of driving wheelbase to overall engine wheelbase | 0.68 |
| Overall Wheelbase (engine & tender) (ft / m) | 50.07 / 15.26 |
| Axle Loading (Maximum Weight per Axle) (lbs / kg) | 35,281 / 16,003 |
| Weight on Drivers (lbs / kg) | 125,441 / 56,899 |
| Engine Weight (lbs / kg) | 145,040 / 65,789 |
| Tender Loaded Weight (lbs / kg) | 102,817 / 46,637 |
| Total Engine and Tender Weight (lbs / kg) | 247,857 / 112,426 |
| Tender Water Capacity (gals / ML) | 4200 / 15.91 |
| Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT) | 7.70 / 7 |
| Minimum weight of rail (calculated) (lb/yd / kg/m) | 52 / 26 |
| Geometry Relating to Tractive Effort | |
| Driver Diameter (in / mm) | 55.50 / 1410 |
| Boiler Pressure (psi / kPa) | 192.40 / 1310 |
| High Pressure Cylinders (dia x stroke) (in / mm) | 20.98" x 27.99" / 533x711 |
| Tractive Effort (lbs / kg) | 36,303 / 16466.78 |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | 3.46 |
| Heating Ability | |
| Tubes (number - dia) (in / mm) | 148 - 1.752" / 44.5 |
| Flues (number - dia) (in / mm) | 21 - 5.118" / 130 |
| Flue/Tube length (ft / m) | 12.30 / 3.75 |
| Firebox Area (sq ft / m2) | 151.02 / 14.03 |
| Grate Area (sq ft / m2) | 28.42 / 2.64 |
| Evaporative Heating Surface (sq ft / m2) | 1321 / 122.73 |
| Superheating Surface (sq ft / m2) | 360 / 33.44 |
| Combined Heating Surface (sq ft / m2) | 1681 / 156.17 |
| Evaporative Heating Surface/Cylinder Volume | 117.95 |
| Computations Relating to Power Output (More Information) | |
| Robert LeMassena's Power Computation | 5468 |
| Same as above plus superheater percentage | 6616 |
| Same as above but substitute firebox area for grate area | 35,158 |
| Power L1 | 8448 |
| Power MT | 593.89 |