Federated Malay States classes O1 to O4
Malayan State Railway classes 561 to 564
To accommodate increased mail traffic, the meter-gauge Federated Malay State Railways ordered class O Pacifics from North British at the end of the 1930s. Due to individual batches built between 1938 and 1946, they were given the designations O1 to O4. They were built to achieve the greatest possible power with a permitted axle load of 11 3/4 tons.
These were the most advanced Pacifics in the FMSR. Lightweight construction was used in many places so that the boiler and engine could still be sufficiently dimensioned. The boiler pressure was chosen to be relatively high at 250 psi to increase power. Three cylinders were also used, which were enlarged by half an inch in the third and fourth series. Other special features were thermic syphons and a rotating valve gear.
They were successfully tested for possible high-speed traffic at 70 mph or 113 km/h, but were not actually used. Although these locomotives were later converted to run on oil, they were soon replaced by diesel locomotives in the fast mail service. They therefore continued to be used in freight transport for a long time.
Technical data
General
| Property | O1, O2 | O3, O4 |
|---|---|---|
| Built | 1938-1939 | 1940, 1946 |
| Manufacturers | North British | |
| Wheel arrangement | 4-6-2 (Pacific) | |
| Gauge | 1,000 mm (Meter gauge) | |
Dimensions and weights
| Property | O1, O2 | O3, O4 |
|---|---|---|
| Wheelbase | 8.61 m | |
| Total wheelbase | 15.72 m | |
| Service mass | 60.5 t | |
| Adhesion mass | 38.7 t | |
| Total mass | 105.5 t | |
| Rigid wheelbase | 3.05 m | |
| Axle load | 13 t | |
| Water capacity | 15,592 l | |
| Fuel capacity | 10,910 l (oil) | |
Boiler
| Property | O1, O2 | O3, O4 |
|---|---|---|
| Grate area | 2.508 m² | |
| Firebox surface | 35.768 m² | |
| Tube heating surface | 103.03 m² | |
| Evaporative heating surface | 138.797 m² | |
| Superheater surface | 20.253 m² | |
| Total heating surface | 159.1 m² | |
Power plant
| Property | O1, O2 | O3, O4 |
|---|---|---|
| Driver diameter | 1,372 mm | |
| Boiler pressure | 17.2 bar | |
| Expansion type | simple expansion | |
| Cylinders | three, 318 x 610 mm | three, 330 x 610 mm |
Power
| Property | O1, O2 | O3, O4 |
|---|---|---|
| Power source | steam | |
| Estimated power | 1,268 kW (1,724 PS) | |
| Starting effort | 98.5 kN | 106.5 kN |
Calculated values
| Property | O1, O2 | O3, O4 |
|---|---|---|
| Factor of adhesion | 1 : 3.86 | 1 : 3.57 |
| Optimal speed | 79 km/h | 72 km/h |
| Power-to-weight ratio | 21.0 kW/t | |
| Heating Surface Equivalent | 358.1 m² | |
| Cylinder volume/HSE | 1 : 404.28 | 1 : 437.27 |
| Adhesive weight/Total | 1 : 1.56 | |
| Tractive force/Heating surface | 1 : 12.93 | 1 : 13.98 |
| Grate area/Heating surface | 1 : 63.42 | |
| Firebox/Tube surface | 1 : 2.88 | |
| Total/Superheater | 1 : 6.85 | |
