Gresley conjugated valve gear
[citation needed] Locomotives with Gresley valve gear must have the three pistons operating at precisely 120 degree intervals.
The resultant timing of the blast from steam exiting the cylinders gives these three-cylinder locomotives a regular exhaust beat.
[3] However, the B17 Class "Footballer"/"Sandringham" 4-6-0s avoided this particular problem by being designed with the conjugated gear behind, rather than in front of, the cylinders.
[4] The main difficulty with this valve gear was that at high speeds, inertial forces caused the long conjugating lever to bend or "whip".
Sustained high speed running could sometimes cause the big end to wear rapidly enough that the increased travel afforded to the middle piston by the increased play in the bearing was enough to knock the ends off the middle cylinder.
LNER Class A4 4468 Mallard suffered centre cylinder big-end damage (indicated to the driver by the fracture of a "stink bomb" attached to the bearing, which fractures during overheating of the white metal) during its world record run and was forced to limp back to its depot for repairs afterwards.
[8] Under later British Railways ownership, the application of former Great Western Railway workshop practices for precise alignment of the valve gear and in the manufacture and lubrication of the inside big end bearing effectively solved the problems.
Some of the Union Pacific 9000 class locomotives were converted to a "double Walschaerts" valve gear, while later examples were built with roller bearings for the moving parts of the Gresley mechanism.
Later VR and NSWGR three cylinder locomotive designs used alternative mechanisms to the Gresley system in an effort to overcome its high maintenance overhead.
[11][12] The Victorian Railways H class of 1941 was fitted with a German Henschel und Sohn conjugated valve gear mechanism which was judged to be superior to the Gresley system.
[13] In New South Wales the D58 class of 1950 replaced the long conjugating lever with a transverse rod, which used a rack and pinion on the right valve stem to rotate a transverse rod, which through a second rack and pinion gave motion to the equal lever pivot.
[11] Gresley valve gear was used on the NZR G class Beyer-Garrett six-cylinder locomotives supplied to the New Zealand Railways in 1928.
The manufacturer Beyer Peacock advised against the three/six-cylinder option with Gresley gear but it was required by G S Lynde the NZR CME.
Designed by Hideo Shima, 97 of these locomotives were built between 1928 and 1929 to haul Tōkaidō Main Line express services, such as the Tsubame and the Fuji, which connected Tokyo and Osaka, the country’s two largest cities.
While they met initial expectations in terms of performance, their mechanical complexity resulted in a short service life, with all locomotives of the class withdrawn by 1950.
One example, C53 45, was rescued from the scrapyard in 1961, restored to haul excursion trains, and is now preserved at the Kyoto Railway Museum.
