SCOA-P pattern wheels are a type of

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the loco ...

wheel A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be ...

. Rather than having traditional solid

spoke A spoke is one of some number of rods radiating from the center of a wheel (the hub where the axle connects), connecting the hub with the round traction surface. The term originally referred to portions of a log that had been riven (split l ...

s, the SCOA-P spoke is hollow, with a 'U' shaped cross section. They are considerably lighter than a conventional spoked wheel or

Boxpok A Boxpok is a steam locomotive wheel that gains its strength through being made of a number of box sections rather than having traditional solid spokes (the name is a variation on "box-spoke"). Being hollow, they allow better counterbalancing and ...

wheel of the same size and strength.

History

SCOA-P wheels were developed in the late 1940s by the Steel Company of Australia Ltd (the P in the acronym standing for F. C. Paynter, who patented the design) in response to

Victorian Railways The Victorian Railways (VR), trading from 1974 as VicRail, was the state-owned operator of most rail transport in the Australian state of Victoria (Australia), Victoria from 1859 to 1983. The first railways in Victoria were private companies, b ...

experiencing fatigue problems with conventional spoked wheels. Stronger Boxpok type 'B' wheels had been installed on a number of VR locomotive classes in the late 1940s, but they had the disadvantage of being relatively heavy and also restricted maintenance access to axleboxes, underslung springs, and in some cases boiler washout plugs. Boxpok wheels were proposed for the forthcoming

Victorian Railways R class The R class was an express passenger steam locomotive that ran on Australia's Victorian Railways (VR) from 1951 to 1974. A long overdue replacement for the 1907-era A2 class 4-6-0, their development and construction was repeatedly delayed due to ...

4-6-4 Under the Whyte notation for the classification of locomotives, represents the wheel arrangement of four leading wheels, six powered and coupled driving wheels and four trailing wheels. In France where the type was first used, it is known as ...

, which had a relatively heavy axle load, but it had been discovered that the use of a Boxpok wheel would make

coupling rod A coupling rod or side rod connects the driving wheels of a locomotive. Steam locomotives in particular usually have them, but some diesel and electric locomotives, especially older ones and shunters, also have them. The coupling rods transfer ...

pin removal difficult. The SCOA-P wheel was developed to allow the strength of the Boxpok design but also provide the maintenance access of a conventional spoked wheel.

Comparative performance

The SCOA-P wheel centre of a 73-inch R class

driving wheel On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons (or turbine, in the case of a steam turbine locomotive). On a conventional, non-articulated locomotive, the driving wheels are all coupled to ...

weighed only , lighter than a Boxpok design of the same diameter and equivalent strength. Using a vertical press, load testing was conducted of the strength and elasticity of the SCOA-P wheel centre against a conventional spoked driving wheel centre of an A2 class locomotive that had the same diameter, but was engineered for a lower

axle load An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearin ...

). The tests revealed that the SCOA-P wheel was still elastic at , with a permanent set occurring at about , whereas the conventional spoked wheel experienced permanent set at .

Use

image:R761 SCOA-P.jpg, SCOA-P driving wheels on

steam locomotive R 761. SCOA-P wheels were used on Victorian Railways' Victorian Railways R class, R class

and J class

2-8-0 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, eight powered and coupled driving wheels on four axles, and no trailing wheels ...

locomotives, introduced in 1951 and 1954 respectively. They were also used on the

Queensland Rail Queensland Rail (QR) is a railway operator in Queensland, Australia. Owned by the Queensland Government, it operates local and long-distance passenger services, as well as owning and maintaining approximately 6,600 kilometres of track and relate ...

ways BB18¼ class

4-6-2 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of four leading wheels on two axles, six powered and coupled driving wheels on three axles and two trailing wheels on one axle. The loco ...

and

Tasmanian Government Railways The Tasmanian Government Railways (TGR) was the former operator of the Rail transport in Tasmania, mainline railways in Tasmania, Australia. Formed in 1872, the railway company was managed by the Government of Tasmania, and existed until absorp ...

M class

and H class

4-8-2 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of four leading wheels, eight powered and coupled driving wheels and two trailing wheels. This type of steam locomotive is commonly known ...

. Because the

Vulcan Foundry The Vulcan Foundry Limited was an English locomotive builder sited at Newton-le-Willows, Lancashire (now Merseyside). History The Vulcan Foundry opened in 1832, as Charles Tayleur and Company to produce girders for bridges, switches, crossi ...

, which built the VR J class, built SCOA-P wheeled locomotives for export until ceasing steam locomotive production in 1956, this wheel type was also seen in many of Vulcan's other export markets. SCOA-P wheel centres were found on locomotives for the Gold Coast Railway in Africa (WM and YL classes), East African Railways (30 and 31 classes), Iran Railways'

2-10-2 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of two leading wheels, ten powered and coupled driving wheels, and two trailing wheels. In the United States of America and elsewhere the is ...

Decapod, and a class of Indian Government Railways'

2-8-4 Under the Whyte notation, a 2-8-4 is a steam locomotive that has two unpowered leading wheels, followed by eight coupled and powered driving wheels, and four trailing wheels. This locomotive type is most often referred to as a Berkshire, though ...

T tank locomotives,Vulcan Foundry Locomotive List - No 6096-9125
- retrieved 30 October 2006 among others.

References

{{Reflist Train wheels

History

Comparative performance

Use

See also

References