Examining the cornish engine

| July/August 1982

The Cornish engine was a most unusual machine. It had neither connecting rod, crank or flywheel, and operated on a single acting cycle which dated back to Watt's first involvement with the steam engine, a cycle which remained unchanged as long as these engines operated. It reached a peak of efficiency in the 1840s not achieved by the normal reciprocating engine for years and yet it was almost exclusively limited in application to water works and mining installations. It was also big; 9' and 10' strokes with bores up to 90' or 100' were common by the middle of the 19th century.

We can examine its decendency from the atmospheric engine in order to better understand its development and operation.

Although the shaft is no longer used for pumping, it served until recently as a ventilating shaft, and air ducts are located behind the concrete walls.

This engine is now preserved and open to the public. Notice the resemblence to the engine house model shown in the July/August issue of IMA.

The windows indicate the three floor levels of these engine houses. The lower one is level with the cylinder bottom; the middle several feet below the cylinder top, and the upper level with the walking beam.

The beam bearings rested on the wall of the engine house itself, and as a result the shaft side wall was heavily built, often being three feet thick.