In 1812 trevithick built the first steam engine of the "so-called cornish" type. the cornish engine was simply a watt single-acting engine employing high-pressure preparing the working principle of this engine was very similar to the watt pumping engine described above. high-pressure and condensing action were combined in a carefully regulated operating cycle (the "cornish cycle"). high-pressure steam was admitted at the top of the cylinder from the inlet valve.