At the very least, this article made me understand why my boiler is made from copper, while the cap and attached group are made from brass!
https://dailycoffeenews.com/2019/05/29/ ... -espresso/
... In essence, espresso machines have been temperature and pressure profiling for 70 years.
Everything we have built since then has been, in one way or another, trying to duplicate what these early machines did with springs and levers.