Great Western Railway class 157
In 1862, Daniel Gooch designed ten standard gauge 2-2-2 express locomotives for the GWR which got the numbers 157 to 166. Built by Sharp, Stewart & Co., they got the nickname “Sharps”. They had double frames and the inside frame only extended from the cylinders to the front of the firebox, while carrying the load of all moving masses. The Firebox of these locomotives was higher than the boiler barrel.
As early as in 1879, they were found to be too weak and scrapped. At the same time, ten similar locomotives were built under William Dean and got the same numbers. These now had a flush-topped boiler and a full-length inside frame. With a larger firebox and a somewhat smaller boiler barrel, the power had been increased in comparison to the 1862 locomotives. Also the wheelbase had increased from 16 feet to 17 ft 8 in. It remains unclear if any parts at all were re-used from the older locomotives.
As they were originally thought to be rebuilds of the earlier locomotives, they carried the nickname “Sharpies”. Another name given to the class was “Cobham” from the name of No. 162. A good part of the class survived into the 20th century, having got new boilers at least once. Some even got a Belpaire firebox. Most were withdrawn between 1903 and 1906, with 165 surviving until 1914.
Technical data
General
| Property | as built | Dean 1879 |
|---|---|---|
| Built | 1862 | 1879 |
| Manufacturers | Sharp, Stewart & Co. | Swindon |
| Wheel arrangement | 2-2-2 (Jenny Lind) | |
| Gauge | 1,435 mm (Standard gauge) | |
Dimensions and weights
| Property | as built | Dean 1879 |
|---|---|---|
| Total wheelbase | 4.88 m | 5.39 m |
| Service mass | 30.2 t | 36.7 t |
| Adhesion mass | 13 t | 16.8 t |
| Rigid wheelbase | 4.88 m | 5.39 m |
| Axle load | 13 t | 16.8 t |
Boiler
| Property | as built | Dean 1879 |
|---|---|---|
| Grate area | 1.358 m² | 1.793 m² |
| Evaporative heating surface | 115.274 m² | 112.809 m² |
| Total heating surface | 115.3 m² | 112.8 m² |
| Firebox surface | 10.684 m² | |
| Tube heating surface | 102.126 m² |
Power plant
| Property | as built | Dean 1879 |
|---|---|---|
| Driver diameter | 2,134 mm | |
| Boiler pressure | 9 bar | 9.7 bar |
| Expansion type | simple expansion | |
| Cylinders | two, 406 x 610 mm | two, 457 x 610 mm |
Power
| Property | as built | Dean 1879 |
|---|---|---|
| Power source | steam | |
| Estimated power | 224 kW (305 PS) | 336 kW (457 PS) |
| Starting effort | 36.0 kN | 49.0 kN |
Calculated values
| Property | as built | Dean 1879 |
|---|---|---|
| Factor of adhesion | 1 : 3.55 | 1 : 3.36 |
| Optimal speed | 39 km/h | 42 km/h |
| Power-to-weight ratio | 7.4 kW/t | 9.1 kW/t |
| Adhesive weight/Total | 1 : 2.32 | 1 : 2.19 |
| Tractive force/Heating surface | 1 : 6.51 | 1 : 9.07 |
| Grate area/Heating surface | 1 : 84.89 | 1 : 62.92 |
| Heating Surface Equivalent | 166.2 m² | |
| Cylinder volume/HSE | 1 : 1,204.11 | |
| Firebox/Tube surface | 1 : 9.56 |