Wardale strongly defends his choice of Walchaerts valve gear and piston valves, and has explained his reasons in several letters, some of which are included in the page titled “Why Walschaerts Valve Gear?”. However a more comprehensive reply is recorded in a letter from David Wardale to John Duncan which is transcribed over 7 pages titled “Piston […]
Chris Newman posed the question: “Why were piston tail rods dropped from latterday designs?” Wardale responded as follows: “Without a tail rod the weight of the piston is taken by its head or by the rings if these are of lipped type. They were dropped because head and linear wear was found to be tolerable […]
Readers have occasionally asked whether consideration was given to applying variable lead to the Walschaerts valve gear on the 5AT. In fact, Wardale did give thought to this and he discusses it in FDC 5 (line 34) where he wrote: Varying lead with cut-off is possible by shortening the eccentric crank length or slotting the […]
The following answer is taken from Wardale’s response to an unpublished letter from Bryan Attewell written in response to Wardale’s two-part article “Steaming into the Future” published in Steam Railway magazines #272 and #273: “Mr Attewell criticises the choice of 2 cylinders for high speed, but the 2-cylinder locomotive cannot be simply condemned without fully […]
There are many people (including many with great knowledge of the subject) who challenge Wardale’s choice of Walschaerts valve for the 5AT, believing that British Caprotti (as used on the BR 8P Pacific No 71000 Duke of Gloucester) would have been a far more appropriate choice because it offers larger port openings and zero back […]
The following comes from a “Is it just a Phantom” – David Wardale’s response to Herr Ebel published in Lok Report in March 2001: “It should be noted that needle roller bearings were an integral part of the American Baker valve gear, and are extensively used on Walschaerts valve gear on Chinese locomotives, operating successfully […]
There has been much debate over the years since this project was initiated as to whether Wardale was mistaken in adopting piston valves driven by Walschaerts valve gear on the 5AT instead of British Caprotti valves driven by rotary cams. The issue is discussed in the FAQ pages and two or three letters on the subject appear […]
Note: With 30 inch piston stroke and 6′ 2″ wheels, the piston speed at the max. design speed of 200 km/h (125 mph) will be 23.8 m/s or 24.8 m/s with worn tyres. David Wardale responds as follows: Whatever the mean piston speed, a piston always moves slowly close to the end of its stroke […]
The effects of “hammer blow” are discussed in the response to the FAQ relating to perceived benefits of a 3-cylinder arrangement. However they are covered in more detail in the Notes on FDC 8 where Wardale’s conclusions are presented as follows: The 5AT locomotive can be satisfactorily balanced for 200 km/h operation by all criteria […]