An Introduction to Large-Lap Valves & Their Use on the LMS




For many years locomotive enthusiasts particularly those who favour the LMS have been led to believe the introduction of large-lap valves (long travel valves) represented the zenith of steam locomotive design. However this was a gross simplification of the true situation.

Other factors served to influence locomotive power, performance and economy and long-travel valves represented but one possible improvement.

This book considers the main influences and by means of reasoned analysis gives careful evaluation of their contribution. This same approach is used to demonstrate when large-laps were a benefit and when they were not.

The Great Western appreciated the truth in this for under Messrs Churchward, and Collet the company built as many (if not more) short-lap engines during the ‘20s and ’30s and later than it did large-lap. Many were simply cosmetically improved replicas of Victorian saturated designs. Yet when contemporary LMS engineers did the same, they were criticised by their successors – men who not only should have known better but also thereby misled generations of enthusiasts. Written by a professionally trained steam engineer, albeit marine, this book is an attempt to right that wrong.

97 pages 17 tables 12 diagrams (one folded in a pocket).