Compound steam engine
Steam engine where steam is expanded in stages / From Wikipedia, the free encyclopedia
For compound steam locomotives, see Compound locomotive.
A compound steam engine unit is a type of steam engine where steam is expanded in two or more stages.[1][2] A typical arrangement for a compound engine is that the steam is first expanded in a high-pressure (HP) cylinder, then having given up heat and losing pressure, it exhausts directly into one or more larger-volume low-pressure (LP) cylinders. Multiple-expansion engines employ additional cylinders, of progressively lower pressure, to extract further energy from the steam.[3]
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Triple_expansion_engine_animation.gif/220px-Triple_expansion_engine_animation.gif)
High-pressure steam (red) passes through three stages, exhausting as low-pressure steam (blue) to the condenser
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/1/18/TMW_677_-_Triple_expansion_compound_steam_engine.jpg/640px-TMW_677_-_Triple_expansion_compound_steam_engine.jpg)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/1/13/Cross-compound_Robey_steam_engine%2C_close-up_of_cylinders%2C_Bolton_museum.jpg/640px-Cross-compound_Robey_steam_engine%2C_close-up_of_cylinders%2C_Bolton_museum.jpg)
small high-pressure cylinder (left) and large low-pressure cylinder (right)
Invented in 1781, this technique was first employed on a Cornish beam engine in 1804. Around 1850, compound engines were first introduced into Lancashire textile mills.