Great Western Railway class 3700 “City”
In 1902, the GWR rebuilt a 4-4-0 Atbara class locomotive with a new domeless taper boiler with Belpaire firebox. This was No. 3405 “Mauritius”, which now served as a prototype for the new City class. Ten more of this type were built in 1903 with numbers 3433 to 3442. In 1907 and 1908, nine more Atbaras were rebuilt, bringing the number of the City class to 20. Soon they were given the numbers 3700 to 3719.
No. 3440 “City of Truro”, which later became 3717 and is considered the first steam locomotive to actually reach 100 mph or 161 km/h, achieved greater fame. This happened on the ninth of May 1904 on the Wellington Bank in Somerset, which had a gradient of 1 in 90. However, due to the inaccuracies of the measurement methods at the time, it is still not entirely clear whether the speed achieved was up to 102.3 or even just 99 mph.
Between 1910 and 1912 all members of the City class received a superheater. Further modifications carried out over the years included the boiler feed, chimney, valves, a steam reverser and a different bogie. All were withdrawn between October 1927 and May 1931. Due to its history, the “City of Truro” is the only one that has been preserved and is now no longer operational.
Technical data
General
| Property | as built | superheated |
|---|---|---|
| Built | 1902-1909 | 1910 |
| Manufacturers | Swindon | |
| Wheel arrangement | 4-4-0 (American) | |
| Gauge | 1,435 mm (Standard gauge) | |
Dimensions and weights
| Property | as built | superheated |
|---|---|---|
| Wheelbase | 6.55 m | |
| Service mass | 56.2 t | |
| Adhesion mass | 36.7 t | |
| Total mass | 93.5 t | |
| Rigid wheelbase | 2.59 m | |
| Axle load | 18.6 t | |
| Water capacity | 16,364 l | |
| Fuel capacity | 5.1 t (coal) | |
Boiler
| Property | as built | superheated |
|---|---|---|
| Grate area | 1.91 m² | |
| Firebox surface | 11.919 m² | 11.958 m² |
| Tube heating surface | 150.661 m² | 125.352 m² |
| Evaporative heating surface | 162.58 m² | 137.311 m² |
| Total heating surface | 162.6 m² | 155.1 m² |
| Superheater surface | 17.837 m² | |
Power plant
| Property | as built | superheated |
|---|---|---|
| Driver diameter | 2,045 mm | |
| Boiler pressure | 13.4 bar | |
| Expansion type | simple expansion | |
| Cylinders | two, 457 x 660 mm | |
Power
| Property | as built | superheated |
|---|---|---|
| Power source | steam | |
| Estimated power | 634 kW (862 PS) | 783 kW (1,065 PS) |
| Starting effort | 77.2 kN | |
Calculated values
| Property | as built | superheated |
|---|---|---|
| Factor of adhesion | 1 : 4.66 | |
| Optimal speed | 50 km/h | 63 km/h |
| Power-to-weight ratio | 11.3 kW/t | 13.9 kW/t |
| Heating Surface Equivalent | 222.2 m² | 232.8 m² |
| Cylinder volume/HSE | 1 : 975.99 | 1 : 931.55 |
| Adhesive weight/Total | 1 : 1.53 | |
| Tractive force/Heating surface | 1 : 9.91 | 1 : 10.39 |
| Grate area/Heating surface | 1 : 85.12 | 1 : 81.23 |
| Firebox/Tube surface | 1 : 12.64 | 1 : 10.48 |
| Total/Superheater | 1 : 7.70 | |