LNWR Webb Problem compounds

Webb, who had succeeded Ramsbottom in 1871, became convinced of the merits of compound expansion (re-using exhaust steam in a low-pressure cylinder). His 1881 design used a most unusual three-cylinder layout: two outside high-pressure cylinders coupled to the rear pair of driving wheels, and one large inside low-pressure cylinder coupled to the leading pair of drivers. The two pairs of drivers were not mechanically coupled — they could rotate independently.

The arrangement was theoretically efficient but proved unsuccessful in practice: the two pairs of drivers tended to rotate at different speeds, particularly when starting, with one pair often slipping wildly while the other did all the work. Despite the operational problems, Webb persisted with compound design for two further classes (Dreadnought and Greater Britain) before abandoning the layout.

The Webb compounds worked LNWR expresses through the 1880s and 1890s, but their reputation was poor. All were withdrawn or rebuilt as simples by 1907 under George Whale, Webb's successor. None were preserved.

Distinctive 2-2-2-2 layout with two pairs of large driving wheels, the leading pair driven by a single large inside low-pressure cylinder and the rear pair by two outside high-pressure cylinders. No coupling rods between the two pairs of drivers.

• Experiment (1882, prototype, not preserved)