LB&SCR I3 class

LB&SCR I3 class

I3 class 32078 at Brighton 19 March 1950

Type and origin Power type Steam Designer D.E. Marsh Builder Brighton Works Build date 1907–1913 Total produced 27

Specifications Configuration 4-4-2T Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 6 in (1.067 m) Driver dia. 6 ft 9 in (2.057 m) Trailing dia. 4 ft 0 in (1.219 m) Loco weight 73 long tons (74.2 t; 81.8 short tons) saturated; 74 long tons (75.2 t; 82.9 short tons) superheated Fuel type Coal Boiler pressure Saturated: 180 psi (1.24 MPa); Superheated: 160 psi (1.10 MPa) Cylinders Two, inside Cylinder size 19 in × 26 in (483 mm × 660 mm)

Performance figures Tractive effort Saturated: 16,700 lbf (74.3 kN); Superheated: 22,100 lbf (98.3 kN)

Career Class I3 Power class GWR: C BR: 3P Axle load class GWR: Red Withdrawn 1944–1952 Disposition All scrapped

The LB&SCR I3 class was a class of 4-4-2 steam tank locomotives designed by D. E. Marsh for suburban passenger service on the London, Brighton and South Coast Railway.

After introducing two unsuccessful designs of 4-4-2 tank locomotive with the I1 and I2 classes, Douglas Earle Marsh learned a lesson and provided a new design with a far larger firebox. The new design was a tank version of Robert Billinton's successful B4 class tender locomotives. At the time of its introduction locomotive engineers were beginning to take an interest in superheating and Marsh therefore ordered two locomotives from Brighton Works for comparative purposes, one with a traditional saturated boiler and one incorporating the Schmidt superheater. These were built in October 1907 and March 1908 respectively.

Several months of trials proved that both locomotives were performing well and reliably but the London, Brighton and South Coast Railway Board of Directors were still not convinced that the extra building costs associated with superheating was matched by lower running costs. Marsh therefore built four more superheated locomotives and six without superheating, between February 1909 and March 1910. By mid 1910 there was sufficient operating data to convince the Directors and all after this date were superheated. Five more locomotives appeared in 1910.

Both varieties of the I3 class proved themselves to be excellent locomotives but the superheated versions were significantly cheaper to run on express trains, especially when compared with the B4 and H1 classes. The class were also used experimentally on through express trains with the London and North Western Railway between Brighton and Rugby and convinced the LNWR directors of the value of superheating. Ten more superheated I3s were constructed in 1912 under Lawson Billinton, with minor detail differences.