[Weter]

There are two separate devices at smoke box: the conus(may consist of up to four and even more nozzles) releases (exhausts) worked steam from cylinders during motion (there was topic about pulsating smoke here)
The syphon (I think this is that thing, named "blower" in English tradition) is controlled by crew, uses fresh (live) steam from boiler directly, being regulated by the valve.
As this is a steam-consumer, it can be totally cut-off, when unnecessary- just as it done in MSTS/ORTS. Used to raise fire, to increase draft in tunnels-as MSTS manual told.

Advanced steamers have folding walves, that begin to work only when the steam pressure in intake tubes are grater, than in cylinders, but when you close regulator, walves are folding and stop making resistance for pistons moving during locomotive coast, as well as preventing the draft of exhaust gases to cylinders thru conus, as it really harmful, as we're told.
Excursion to smoke box and then-firebox.
https://m.youtube.co...h?v=gb1NtNgzNfk
https://m.youtube.co...h?v=GmGOQX0F-BE