| Driving Wheels | 4ft 0ins |
| Boiler Pressure | 200psi |
| Cylinders | Outside – 16in x 24in |
| Tractive Effort | 21,760lbf |
| Valve Gear | Walschaert |
The design of the class W locomotives originated in 1947 with Frederick Mills who was the Chief Mechanical Engineer of the Western Australian Government Railways (WAGR). When he died in in 1949 his successor Charles Clarke progressed the design.
Mills had requested Beyer, Peacock & Company to reserve capacity for their construction when the design was first proposed, however, by the time Clarke took over, Beyer, Peacock & Co had identified a number of possible problems with the design. Following a meeting of the designer and constructer the locomotive was substantially redesigned.
The resultant locomotive included many proprietary boiler and ancillary fittings, as well as parts interchange ability. The firebox was substantially altered to take into account the properties of Collie coal. This included a combustion chamber, thermic syphons and arch bar tubes.
The running gear was based heavily on Beyer, Peacock & Co’s Standard Light Garratt design, which was built for the South Australian Railways as its 400 class. The first 40 were delivered partially erected, whilst the final 20 were fully assembled prior to shipping. The last 20 had larger tenders, capable of holding an additional 550 gallons. All were delivered between April 1951 and June 1952.
Four locomotives were also supplied by Beyer, Peacock & Company for the Silverton Tramway which were also categorised as the W class. These locomotives did have some differences from the WAGR W class including a skyline cowling running the length of the boiler and smokebox, Westinghouse air brakes, and an additional blow-down valve in the middle of the bottom of the boiler barrel.
The axle load of the WAGR locomotives was only 9.5tons which meant that they could travel over the entire WAGR network. They were essentially a freight engines but regularly hauled The Australind from Perth to Bunbury.
The class had a reputation for being free steamers and strong pullers. Although they have a well-deserved reputation for their reliability, like any new class the W locos suffered some minor teething problems, including ashpan failures, and leaks in and around the foundation ring. The leaks were traced to faulty welding. The class suffered from stay failures in its early days, particularly in and around the throat plate.
At one point, no fewer than 34 of the class were in Midland Railway Workshops or regional depots for stay repair. The problem was traced back to the thermic syphons creating significant water movement in the area, overstressing the boiler plates, as well as problems with the quality of the original stays. The syphons were progressively removed over a seven-year period so that by 1959 the problem had been eliminated.
As the WAGR moved to diesel power the W class locomotives were gradually moved to the southern parts of the network. The first locomotives were withdrawn from service in 1968 and the last in 1972. Some were retained in reserve at Midland until 1980.
As the locomotives were relatively new when taken out of service and because of the light axle load the locomotives were regarded as ideal for tourist operators and hence a significant number of the W class locomotives have been preserved.
This locomotive (W 901) was built by Beyer, Peacock & Company at Manchester in 1951 and entered service in April that year as the first locomotive of the W class.
It entered preservation in 1978 when it was purchased by the Steamtown Peterborough Preservation Society in South Australia to where it was delivered in early 1979.
The locomotive was restored to steam at Steamtown and operated over the isolated 3ft 6in gauge line from Peterborough to Orrorroo, The operation of steam trains over the line ceased in 2002 due to the high cost of maintaining the aging permanent way.
W901 is now on static display in the roundhouse at the Steamtown Rail Heritage Museum.
There are another 14 members of the WAGR W class built by Beyer, Peacock & Company preserved.
- 901 – Works number 7378
- 903 – Works number 7380
- 907 – Works number 7384
- 908 – Works number 7385
- 916 – Works number 7393
- 919 – Works number 7396
- 920 – Works number 7397
- 924 – Works number 7401
- 931 – Works number 7408
- 933 – Works number 7410
- 934 – Works number 7411
- 943 – Works number 7455
- 945 – Works number 7457
- 947 – Works number 7459
- 953 – Works number 7465
Three of the four locomotives built for the Silverton Tramway have been preserved.
- W22 – Works number 7418
- W24 – Works number 7552
- W25 – Works number 7553
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