Block diagram of two stage steam engine?

Answer 1

You can't give diagrams on a basic text-editor like this one!

To explain for reciprocating engines:

A "Two-stage" steam-engine is properly called "compound", and consists of 2 cylinders each with its own piston, piston-rod, crosshead and connecting-rod linked to the single crankshaft.

The "live" steam at high-pressure (from the boiler via the throttle-valve or regulator, and superheater) is admitted to the first cylinder and partially expanded during its working stroke there. On exhaust it is the sent to the second cylinder and expanded further.

The steam is thus expanded through a much larger pressure-gradient than would be the case in a "simple expansion" engine, hence obtaining the maximum practicable power from each does of steam. The only other way you can do that is to use an unfeasibly long cylinder, since steam expands roughly hyperbolically, according to the Gas Laws: pressure X volume = a constant.

To compensate for the steam in the second cylinder being at a much lower starting pressure, that, the Low-pressure Cylinder, is of larger diameter than the High-pressure Cylinder, to equalise the force acting upon both pistons. Larger engines were also built, with an interposed Intermediate pressure Cylinder (Triple Expansion), and some of the largest had a fourth cylinder still. The effect is the same - obtaining the most work from a given quantity of steam.

Incidentally you sometimes hear people describe compound engines as using "the same steam twice". That is wrong, but even professional traction-engine drivers and the like in the late-19 / early-20C held this misunderstanding.

The steam-turbine.

A steam-turbine is a form of compound steam-engine, though rotary not reciprocating, because it expands the steam from inlet to exhaust through the blades on a series of progressively larger discs along the rotor.As pressure falls along the series, the disc radius increases to equalise the torques produced by each disc.