SR Z Class

SR Z class

BR Z class 30951 at Exeter Central, 1960

Type and origin Power type Steam Designer Richard Maunsell Builder SR Brighton Works Build date 1929 Total produced 8

Specifications Configuration 0-8-0T UIC class D n3t Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Driver dia. 4 ft 8 in (1.422 m) Length 39 ft 4 in (11.99 m) Loco weight 71 long tons 12 cwt (160,400 lb or 72.7 t) 72.7 t; 80.2 short tons Fuel type Coal Fuel capacity 3 long tons 0 cwt (6,700 lb or 3 t) 3.0 t; 3.4 short tons Water cap 1,500 imp gal (6,800 l; 1,800 US gal) Firebox:  • Firegrate area 18.6 square feet (1.73 m2) Boiler pressure 180 psi (1.24 MPa) Cylinders 3 Cylinder size 16 in × 28 in (406 mm × 711 mm)

Performance figures Tractive effort 29,376 lbf (130.67 kN)

Career Operators Southern Railway → British Railways Class SR: Z Power class BR: 7F Numbers SR: 950–957 BR: 30950–30957 Withdrawn 1962 Disposition All scrapped

The SR Z class was an 0-8-0T 3-cylinder tank engine designed by Richard Maunsell and intended for heavy shunting on the Southern Railway, the first eight entering into service in 1929. It was a successful design and would have been built in greater numbers, but an order for a further ten was cancelled in 1930 due to the reduction in freight traffic as a result of the Great Depression.

The newly amalgamated Southern Railway needed a group of powerful shunting tank locomotives to work in its marshalling yards around London and on freight transfers between them. Robert Urie's G16 class 4-8-0 performed this task well, and further examples were on order in 1922, but Richard Maunsell considered the firebox to be too large and the superheater an unnecessary expense on such locomotives. He therefore cancelled the order in favour of a new design.

Due to the requirement for heavy shunting, the design was provided with an 0-8-0 wheel arrangement to increase traction, whilst enabling the locomotives to negotiate tight curves prevalent in goods yards. Another requirement was for the locomotive to be able to maintain power after long periods of standing idle, as freight marshalling was an intermittent duty. A 1,500-imperial-gallon (6,800 l; 1,800 US gal) water capacity was also required to reduce the need for regular watering.

The new class was largely designed at Ashford railway works but, as a result of the unexpected need to redesign and rebuild the SECR K class locomotives at Ashford, Maunsell decided to construct the Z class at Brighton. One result of this change was that the boiler used was of an existing Brighton design, that of the D.E. Marsh C3 class. The resultant design was a three-cylinder locomotive that incorporated Walschaerts outside valve gear, driving the third axle and a custom-built inside gear driving the second. The first of the class emerged from Brighton in March 1929 followed by the remainder over the next six months.