Trevithick's high-pressure expansive
steam condensing pole-engine, as erected at Wheal Prosper mine in 1811-12. The plunger pole steam engine is based on the water-powered plunger pump developed by Trevithick in 1798. It uses high pressure steam to move the piston inside its long pole case. At Wheal Prosper, the two boilers used for it were capable of working at 690kN per sq m (100psi).
Illustration: Cornish Studies Library © Cornwall County Council