Southern Pacific classes MK-5 and MK-6
The classes MK-5 and MK-6 consisted of a total of 94 Mikados built for the Southern Pacific and its subsidiary Texas & New Orleans between 1913 and 1921. In contrast to earlier SP Mikados they were a Harriman standard design and had taller drivers and larger cylinders. 17 of the actual class MK-5 were built by Baldwin and Lima between 1913 and 1917. 20 more which were only built by Lima were designated class MK-6.
The T&NO got a total of 57 MK-5. Most were built by Baldwin, ALCO-Brooks and the SP Algiers shops, with only one delivered from the Houston shops. All of these had disappeared by 1957. Today four MK-5 are still existing, even though none is currently operational. While 771 will remain stationary, 745 was operational again since 2004 and is currently being restored. 786 is being restored for the first time, while there are plans to do the same with 794.
Technical data
General
| Property | T&NO | SP |
|---|---|---|
| Built | 1913-1921 | 1913-1917 |
| Manufacturers | Baldwin, ALCO, Algiers, Houston | Baldwin, Lima |
| Wheel arrangement | 2-8-2 (Mikado) | |
| Gauge | 1,435 mm (Standard gauge) | |
Dimensions and weights
| Property | T&NO | SP |
|---|---|---|
| Wheelbase | 10.72 m | |
| Total wheelbase | 24.44 m | |
| Service mass | 129.7 t | 127.4 t |
| Adhesion mass | 96.8 t | 97.1 t |
| Total mass | 200.5 t | 204.6 t |
| Rigid wheelbase | 5.03 m | |
| Axle load | 24.6 t | 24.7 t |
| Water capacity | 34,069 l | |
| Fuel capacity | 11,129 l (oil) | |
Boiler
| Property | T&NO | SP |
|---|---|---|
| Grate area | 6.54 m² | |
| Firebox surface | 21.832 m² | 22.483 m² |
| Tube heating surface | 347.365 m² | 369.104 m² |
| Evaporative heating surface | 369.197 m² | 391.587 m² |
| Superheater surface | 80.361 m² | 82.684 m² |
| Total heating surface | 449.6 m² | 474.3 m² |
Power plant
| Property | T&NO | SP |
|---|---|---|
| Driver diameter | 1,600 mm | |
| Boiler pressure | 13.8 bar | |
| Expansion type | simple expansion | |
| Cylinders | two, 660 x 711 mm | |
Power
| Property | T&NO | SP |
|---|---|---|
| Power source | steam | |
| Estimated power | 2,200 kW (2,991 PS) | 2,237 kW (3,041 PS) |
| Starting effort | 227.2 kN | |
Calculated values
| Property | T&NO | SP |
|---|---|---|
| Factor of adhesion | 1 : 4.18 | 1 : 4.19 |
| Optimal speed | 60 km/h | |
| Power-to-weight ratio | 17.0 kW/t | 17.6 kW/t |
| Heating Surface Equivalent | 639.1 m² | 669.4 m² |
| Cylinder volume/HSE | 1 : 762.38 | 1 : 727.88 |
| Adhesive weight/Total | 1 : 1.34 | 1 : 1.31 |
| Tractive force/Heating surface | 1 : 10.56 | 1 : 10.01 |
| Grate area/Heating surface | 1 : 68.74 | 1 : 72.52 |
| Firebox/Tube surface | 1 : 15.91 | 1 : 16.42 |
| Total/Superheater | 1 : 4.59 | 1 : 4.74 |
