Kylchap

The Kylchap steam locomotive exhaust system was designed and patented by French steam engineer André Chapelon, using a second-stage nozzle designed by the Finnish engineer Kyösti Kylälä and known as the Kylälä spreader; thus the name KylChap for this design.

Construction

The Kylchap exhaust consists of four stacked nozzles, the first exhaust nozzle (UK: blastpipe) blowing exhaust steam only and known as the primary nozzle, this being a Chapelon design using four triangular jets. This exhausts into the second stage, the Kylälä spreader, which mixes the exhaust steam with some of the smokebox gases; this then exhausts into a third stage, designed by Chapelon, that mixes the resulting steam/smokebox gases mixture with yet more smokebox gases. The four nozzles of this then exhaust into the fourth stage, the classic chimney (U.S.: stack) bell-mouth.

Theory

It was Chapelon's theory that such a multi-stage mixing and suction arrangement would be more efficient than the single stage arrangement hitherto popular in steam locomotive draughting, in which an exhaust nozzle simply is fired up the middle of the stack bell-mouth. It would also ensure a more even flow through all the firetubes, rather than concentrating the suction on one area. The efficiency of the Kylchap system relied on careful proportioning of its components, and perfect alignment and concentricity.