Blower nozzles: I had always imagined that blower steam was simply exhausted up the chimney through the blast pipe when no exhaust steam was available to create a draught. I noticed on plates 52 and 53 of your book "Red Devil and Other Tales from the Age of Steam" that 3450's Lempor system had separate (very small diameter) blower nozzles spaced around the outside of the Lempor nozzles. I presume they are much smaller because the steam pressure delivered to the blower is much higher than that coming through the Lempor nozzles. Do they have separate mixing chambers? And does the presence of blower steam in the chimney cause any interference with the exhaust steam when the locomotive running? Answer: Blower steam has no separate mixing chamber; it is fed into the chimney where mixing occurs. Blower nozzles are smaller because of higher steam pressure and low vacuum requirements, see FDC 12 pages 13/14. If the blower is used when steaming, it merely adds to the input kinetic energy hence gives higher gas pumping - the blower could be turned on to augment the exhaust steam if an engine was steaming very badly.
Lempor Nozzles: With reference to the same photos and the accompanying note that the badly worn Lempor nozzles of 3450 had produced no noticeable reduction in draught, can one deduce that the geometry of the nozzles is not as critical as might otherwise be assumed? Answer: Yes, Lempor nozzle shape does not seem to be so critical - see "The Red Devil" page 475 point (i).
Kordina: I had to re-read "The Red Devil" to figure out just what the Kordina is for. Do I understand correctly that its purpose is to reduce the diameter of each steam exhaust duct before they join, so that throttling occurs in the duct rather than at the blast nozzle which can cause exhaust steam from one cylinder to blow back down the opposite cylinder's exhaust duct? Answer: It should be expressed that the Kordina is to create a region of low pressure and high velocity at the exhaust passage junction so that steam does not back-flow into the opposite cylinder during release.
Swirl Plates: I am still vague about the purpose of the swirl plates at the end of the Kordina in 3450, but deduce that they are introduced to improve the air-gas mixing in as the steam enters the mixing chamber. If so, what effect does swirling have? Is it simply that "swirling" is conducive to "mixing" therefore the addition of swirl plates improves mixing? Is the effect quantifiable? Answer: Swirl was given for the reason you say, to improve steam-gas mixing downstream of the blast nozzles (Porta’s suggestion) see "The Red Devil" bottom of page 153: but this was not beneficial with multiple jet nozzles, see "The Red Devil" page 476 point (v). The figures for FDC 12 include the proposed 5AT Kordina, which is a new design.
Note: Wardale has also commented about the 5AT exhaust system at much greater length in correspondence with Jos Koopmans that covered elsewhere in these FAQs.