Early life, GWR service and Holcroft conjugated valve gear
Holcroft was born in Wolverhampton and undertook a premium apprenticeship at the Wolverhampton works of the GWR. He worked in the assembly shop and the drawing office to get an all-round feel for railway life, giving him the experience to generate his own ideas. His first patent was filed at the age of 18, which brought Holcroft to the attention of Churchward and enabled him to transfer to Swindon works when his apprenticeship was completed. As one of Churchward's rising prodigies in the heyday of GWR locomotive development, Holcroft helped with the design of several of Churchward's locomotives, notably the 4300 class 2-6-0. In 1909, he patented a form of conjugated valve gear to drive the valves of a three-cylinder engine from only two sets of valve gear.
Service with the SECR and the Southern Railway
When the Churchward development programme of new locomotives began to slow down, Holcroft sought employment with a railway still in need of original design work. He joined Richard Maunsell's design team as an Assistant, participating in the latter's contributions to the SECR and Southern Railway's motive power. He collaborated with Nigel Gresley to develop the Gresley conjugated valve gear for 3-cylinder locomotives as fitted to LNER 3 cylinder locomotives. Holcroft continued to develop this mechanism by driving the middle cylinder gear of a steam locomotive from the outside cylinder combination levers, as opposed to Gresley's method of using direct transmission from the front valve spindles. This was necessary in the case of the SECR / SR Moguls because there was insufficient space for Holcroft's original gear to fit between the cylinder leading wheels and first drivers. Holcroft's method had a number of advantages. The Gresley design of conjugated valve gear suffered from variations in valve events brought about by heat expansion of the valve spindles and flexing of the combination lever – even after considerable re-design of the lever and pivot bracket, affecting the valve events when the locomotive was under way. By using the combination lever assembly to drive the middle cylinder, Holcroft managed to circumvent these problems. Subsequently the problem of flexure and lost motion caused the gear to be removed from the SR Moguls in 1931, to be replaced by a third set of Walschaerts gear, as allowed for in the original design. Holcroft's ideas for conjugated valve gear were incorporated into Maunsell's N1 class, K1 class and U1 class three-cylinder locomotives. Holcroft was involved in trials of the Anderson recompression system between 1930 and 1935. He stayed with the Southern Railway after Maunsell's retirement in 1937 to work with Oliver Bulleid.
Retirement
Holcroft retired from the Southern Railway in 1946, and worked on periodicals for the Institution of Civil Engineers. He died in Tadworth, Surrey on 15 February 1973. Holcroft wrote a book, Locomotive Adventure about his experiences regarding the development of steam locomotives in Britain. He was also editor of Railway Engineering Abstracts. A collection of Holcroft's papers is archived at the National Railway Museum, and includes the manuscript for a second autobiography entitled Life with Locos.
Patents
GB190428183, published 23 November 1905, Improved means for use in operating continuous brakes by a vacuum or compressed air
GB190907859, published 25 November 1909, Improvements in or relating to valve gears for engines worked by fluid pressure
