LNWR Webb Problem compounds
The LNWR Webb Compound 'Problem' Class — officially the Experiment Class of 1882 and sometimes referred to as Webb's first series of compound express locomotives — was Francis Webb's initial attempt to build a compound express engine for the London and North Western Railway, predating the Dreadnought Class and representing his first practical experiment with the expansion system that he would pursue obsessively for the remainder of his time at Crewe. Webb had become convinced by French compound locomotive practice, particularly the work of Anatole Mallet and Auguste de Glehn on the Continent, that expanding steam twice — first through high-pressure cylinders, then through larger low-pressure cylinders — could dramatically reduce coal and water consumption on the LNWR's express passenger services.
The Experiment Class of 1882 (not to be confused with the later unrelated Experiment Class of 1905 under Whale) used a 2-2-2-2 wheel arrangement with two uncoupled sets of driving wheels: the small high-pressure inside cylinders drove the rear pair of wheels while the large low-pressure outside cylinders drove the front pair. This uncoupled arrangement — which would persist through all Webb's subsequent compound designs including the Dreadnought and Greater Britain classes — was based on the theoretical argument that compound expansion required mechanically independent cylinder actions, but in practice it created the fundamental operational problem that plagued all Webb's compounds: the two driving axles could rotate independently, causing simultaneous slipping in opposite directions and making starting from rest on any gradient exceptionally difficult.
Despite the operational difficulties, Webb built 30 examples of the Experiment Class between 1882 and 1884, driven by his conviction that the efficiency advantages of compounding justified the operational complexity. Contemporary accounts describe the Experiment Class as performing well at speed when running freely but being almost unmanageable on starts. Webb rebuilt most examples after modest service periods, and his successor Whale converted the survivors to simple expansion. None was preserved in compound form.
Design and development
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.
Service and withdrawals
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.
Identification features
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.
Notable locomotives
- Experiment (1882, prototype, not preserved)
Allocations and regions
Crewe North for WCML express working, though operational unreliability limited consistent deployment on the most demanding schedules.
