Author here. The beam engine created power from steam, and was a key part of the early Industrial Revolution. The article is a deep dive into the engine: how it works, the history behind it, and the engineering tradeoffs the builders faced. There are quite a few interactive figures that I hope make the concepts easier to see.
Building things up from first principles, and ideally also tactile / visceral examples, is my absolute favourite genre of explanations. Alas, a rarefied genre, because it is so much harder to do well (without doing disservice to the learner's intellect and ability) than expert talking to (presumed) expert. So thanks for contributing to it.
People like George Polya [0], Richard Feynman [1], Grace Hopper [2] are exemplars of this tradition.
[0] https://www.youtube.com/watch?v=h0gbw-Ur_do
[1] https://www.youtube.com/watch?v=EKWGGDXe5MA
[2] https://www.youtube.com/watch?v=ZR0ujwlvbkQ
(And I too try in my own meagre way through my blog and source code, albeit it's all plain text because visual explainers, animated ones that too are ridiculously difficult. So I have some idea of how much of a labour of love your piece is. .)