The Cornish engine

When the Watt-patent had expired, in 1800, lots of engineers started developing improvements on the Watt-engine. Richard Trevithick of course was one of them, but he for sure wasn't the most important one.

Diagram of a Cornish beamengineFamous names of engineers involved are Hornblower, Woolf and Lean. Changes were higher pressure, compound, inverted engines, double acting, cast beam, piston sealing etc.

The earlier invented cataract is also used on Cornish engines.

The engine was built in several forms, the ordinary beam-engine, inverted engines and half-beam engines. Wooden beams were no longer used, all beams were made of cast-iron now.

Cornish engines can go up to a pistondiameter of 100 inch, in Holland there is even an engine with a piston of 144 inch.

In the Cornish engine fresh steam of about 3 bar enters the cilinder on top of the piston. The piston is pushed down. When the piston is down the equilibrium-valve is opened, connecting upper and lower part of the cilinder. The weight of the pump-part pulls the beam up and the piston goes easily up, with the pressure both under and on top of the piston being in equilibrium.

When the piston is up, the inlet-valve opens and the fresh steam pushes the piston down. At the same time the outlet-valve in the bottom of the cilinder opens and the steam at the bottom is sucked out, to the condensor. So there is a double force on the piston, steampressure on top and vacuĆ¼m on the bottom.

A Cornish engine can do at about 10 strokes per minute.

The Cornish engine was very successfull, almost all existing beam-engines were converted to the Cornish style. Nowadays many engines can be found all over England, a collection of working engines can be found in Kew Bridge Steam Museum.