Kuhn slide
Encyclopedia
Valve gear
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...
on steam locomotives and is named after its inventor, Michaal Kuhn (1851-1903). The term is also used to refer to this particular type of Walschaerts valve gear system as a whole.
Problems often arise in incorporating a Walschaerts valve gear into the design of tank and narrow gauge
Narrow gauge
A narrow gauge railway is a railway that has a track gauge narrower than the of standard gauge railways. Most existing narrow gauge railways have gauges of between and .- Overview :...
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 (German: Hängeeisen) 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.
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.
A variation of the Kuhn slide was developed by the Lokomotivfabrik 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.