Pm Class Steam Locomotive
Pm 701
| Builder: North British Locomotive Co |
| Coupled Wheel Diameter 4' 6" |
| Total Weight 109 tons 1 cwt |
| Tractive Effort 25,855 lbs |
| Coal Capacity 8 tons |
| Water Capacity 4000 gallons |
| Total number in Service 35 |
After the Second World War the Western Australian Government Railways was in a rundown state. Many of the older locomotives were basically worn out and much essential maintenance had been deferred during the war years. Plans had been made for the construction of ten Pr class locomotives at Midland Workshops and for twenty-five improved Pr class locomotives to be ordered from the United Kingdom. Midland Workshops however was unable to undertake new construction due to amount of essential maintenance. Thirty five locomotives were therefore ordered from the North British Locomotive Company to become the Pm class. The last sixteen were built with roller bearings on the driving axles and sub classified as Pmr.
The Pm class differed from the earlier Pr class with provision of roller bearings on the carrying wheels on the Pm and on all axles on the Pmr class as well as improvements to the cylinders and provision of steam powered reversing gear. A departure from standard WAGR practice was the decision to have independently sprung driving wheels. On the road the independent springing was not a success. The Pm class was not able to keep to express passenger speeds due to rough riding as well as problems with poor adhesion on starting due to weight transfer. Modification to compensated springing on the coupled wheels did not offer any improvement. The class was therefore relegated to hauling fast goods and perishable traffic. The locomotives lasted until the end of steam operation in 1971.
In addition to Pm 701 preserved at Bassendean the Hotham Valley Tourist Railway has restored Pm 706 to working order for use on tour trains.