The Kuhn slide () is part of a modified Walschaerts (German: ''Heusinger'') valve gear on

steam locomotives A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

and is named after its inventor, Michael Kuhn (1851–1903). The term is also used to refer to this particular type of Walschaerts valve gear system as a whole.

Overview

Problems often arise in incorporating a Walschaerts valve gear into the design of

tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful engi ...

and

narrow gauge A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge narrower than standard . Most narrow-gauge railways are between and . Since narrow-gauge railways are usually built with tighter curves, smaller structu ...

locomotives because of space limitations. The reversing rod (with its lifting arm), needed to change between forward and reverse running, is therefore mounted at the same level as the pivot of the expansion link. This enables the lifting link (') to be dispensed with, and the lifting arm to be connected directly to the radius rod. To ensure the required horizontal movement, the back end of the radius rod is designed as a slide (the 'Kuhn slide') which fits into a rotatable crosshead (''Gleitstein'') in the lifting arm.

Advantages

The Kuhn valve gear was not as widespread as the classic Walschaerts valve gear as its production costs were higher. One advantage of the Kuhn slide is that it runs equally smoothly in either direction. For that reason it was preferred on tank locomotives which, for operational reasons, often had to run backwards for long periods. One locomotive that benefited was the

Prussian P 8 The Prussian Class P 8 of the Prussian state railways (DRG Class 38.10-40 of the Deutsche Reichsbahn) was a 4-6-0 steam locomotive built from 1906 to 1923 by the Berliner Maschinenbau (previously Schwartzkopff) and twelve other German factories. Th ...

. After the first 250 were built, the valve gear was changed and the Kuhn slide was added. Together with larger counterweights on the driving wheels improved the locomotives running characteristics.''Die preußische P 8 - die Beste!''
at lok-magazin.de. Retrieved 12 May 2023.

Variations

A variation of the Kuhn slide was developed by the Winterthur Locomotive Works. On the so-called Winterthur valve gear the expansion link itself is attached to the reversing shaft, both having a common pivot.

References

{{steam engine configurations Steam locomotive technologies Locomotive parts Locomotive valve gear