A facebook post spawned a desire to cover this topic of secondary air, and why smoke is made. Hopefully it helps your understanding of locomotives :)

Special thanks to Dynamo Productions for letting me use their footage:
   • [4K] Reading & Northern Doubleheader ...  
   • Southern Pacific 2472 Steam Train  

LMS Training Video, uploaded by the Bennett Brook Railway:
   • LMS training video  Little & Often  

Merch: https://hyce.creatorspring.com/

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   / @hyce777