London & South Western 4-2-2-0 Locomotives in Great_Britain

Class Details by Steve Llanso of Sweat House Media

Class T7 (Locobase 9962)

Data from "Mechanical Engineering", Engineer, Volume 85, No 1 (7 January 1898), pp. 16-17; "New Locomotive Types of 1897",The Railway World, Volume VII [7] (7 April 1898), pp. 120, 129; "An English Four-Cylinder Engine" Railroad Gazette, Volume XXX [30], No 38 (23 September 1898), p. 683; Ernest L Ahrons, The British Steam Locomotive from 1825 to 1925 (London: Ian Allan, 1927), p. 301-302; Michael Duffy, "Rail Stresses, Impact Loading, and Locomotive Design" in History of Technology No 9 (London: Bloomsbury Academic, 1984), p. 61; and "LSWR T7 class" in Wikipedia encyclopedia at [], last accessed on 17 July 2022. (Note: David Maidment's 2020 ebook L & S W R Drummond Passenger & Mixed Traffic Locomotive Classes: A Survey & Overview offers considerable operational detail on the T7 and E10s.

(Thanks to Alexander Blessing for his 29 January 2022 email noting the absence of a T7 record, which led to Locobase's rediscovering this earlier entry lableled only by the engine number, and supplying Locobase with details on the design and a link.)

This single Eight-wheeler was spun from the C8 class of engines (Locobase 9671) to explore the power available in a four-cylinder layout in which inside cylinders drove the front driving axle and outside cylinders turned the rear axle. The goal was to produce a locomotive powerful enough to do without a pilot (helper) locomotive.

The "Double Singles's inside valves followed a typical pattern; they lay between the two cylinders and were actuated by link motion. Valves supplying the outside cylinders were set below the cylinders. Railroad Gazette commented "there is some advantage in this arrangement as it enables the valves to drop from their seats when the engine is running without steam."

All four valves used a "very ingenious" steam-assisted reversing gear, added the Engineer's account, that could set all four using a single lever from the cab. Railway World noted that the original set of cylinders were to have 16 1/2" (419 mm) diameters, but were reduced to match the boiler's steaming capacity. Still later, the boiler's inability to supply adequately four single-expansion cylinders led to a reduction in diameter to 14" (356 mm) each. Total cylinder volume decreased from 10.64 cu ft to 9.26 cu ft

Spacing the drivers an unusually long 11 ft apart allowed for the long firebox whose basic firebox heating surface area came to 142 sq ft (13.19 sq m). This was supplemented by Drummond's cross-firebox water tubes that added another 215 sq ft (19.97 sq m) of heating surface that Engineering calculated afforded a 3:1 greater heat transfer than the firetubes in the boiler.

A 1905 boiler redesign increased tube heating surface area to 1,392 sq ft (129.32 sq m), reduced water tube area to 195 sq ft (18.12 sq m), and increased basic surface area to 173 sq ft (16.07 sq m). Total firebox heating surface area decreased by 26 sq ft (2.42 sq m). Total evaporative heating surface increased to 1,760 sq ft (163.51 sq m).

Five E10 Double Singles (road numbers 369-373), often described as the "production version" of the T7, emerged from Nine Elms in 1901. Although they followed the original design, their boilers

Ahrons noted the 720's design "was never copied on any other railway." He acknowledged the advantages of the design's choice to divide power and use a long firebox. "But", he added, "it had the disadvantage of irregular turning moment, and also irregular balancing effects owing to the absence of coupling rods."

Michael Duffy summarized the shortcomings of uncoupled divided drive in a different way: "Leaving off the coupling rods ...resulted in a tendency for the 'Double-Singles' to slip excessively, wherever they operated ...What is more, as the two sets of driving wheels could slip independently, the four cranks could get out of the phase in which the reciprocating masses provided self-balance."

Blessing notes that the six locomotives remained on the roster when the L&SWR was folded into the Southern Railway. The last of them was retired in 1927.

Principal Dimensions by Steve Llanso of Sweat House Media

Locobase ID9962
RailroadLondon & South Western
CountryGreat Britain
Number in Class1
Road Numbers720
Number Built1
BuilderNine Elms
Valve GearStephenson and Joy
Locomotive Length and Weight
Driver Wheelbase (ft / m)11 / 3.35
Engine Wheelbase (ft / m)26 / 7.92
Ratio of driving wheelbase to overall engine wheelbase 0.42
Overall Wheelbase (engine & tender) (ft / m)50.50 / 15.39
Axle Loading (Maximum Weight per Axle) (lbs / kg)42,336 / 19,203
Weight on Drivers (lbs / kg)84,448 / 38,305
Engine Weight (lbs / kg)122,192 / 55,425
Tender Loaded Weight (lbs / kg)106,064 / 48,110
Total Engine and Tender Weight (lbs / kg)228,256 / 103,535
Tender Water Capacity (gals / ML)5160 / 19.55
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT) 5.50 / 5
Minimum weight of rail (calculated) (lb/yd / kg/m)
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)78 / 1981
Boiler Pressure (psi / kPa)175 / 12.10
High Pressure Cylinders (dia x stroke) (in / mm)15" x 26" / 381x660 (4)
Tractive Effort (lbs / kg)22,313 / 10121.02
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.78
Heating Ability
Tubes (number - dia) (in / mm)277 - 1.5" / 0
Flues (number - dia) (in / mm)
Flue/Tube length (ft / m)12
Firebox Area (sq ft / m2)394 / 36.60
Grate Area (sq ft / m2)27.40 / 2.55
Evaporative Heating Surface (sq ft / m2)1701 / 158.03
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)1701 / 158.03
Evaporative Heating Surface/Cylinder Volume159.93
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation4795
Same as above plus superheater percentage4795
Same as above but substitute firebox area for grate area68,950
Power L17852
Power MT

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