The drawings of this expansive pole condensing engine are from the dimensions given by Captain Grose who erected it, and by Captain Artha who knew it well.
Wheal Prosper High-pressure Expansive Steam-condensing Pole-Engine, 1811.
Trevithick's Cylindrical Boiler for Wheal Prosper Engine, 1811.
a, cast-iron pole, 16 inches diameter, 8-feet stroke; b, pole-case, a small bit larger in internal diameter than the pole; c, cross-head, fixed on top of pole; d, guides for cross-head; e, side rods connecting the two cross-heads; f, bottom cross-head; g, pump-rod; h, balance-beam, with box for weights; i, connecting rods from balance-beam to bottom cross-head; k, guides for air-pump cross-head; l, cross-head and side rods for working air-pump; m, air-pump, condenser, and water-cistern; n, feed-pump worked from air-pump cross-head; o, plug-rod worked from balance-beam; p, exhaust-valve; q, steam-valve; r, exhaust-pipe; s, steam-pipe; t, bracket for carrying working gear; u, expansive steam-horn and tappets; v, handles for working valves.
Detail of Boilers:—a, two wrought-iron boilers, 3 feet in diameter, 40 feet long, using steam of 100 lbs. on the square inch above the atmosphere; b, cast-iron manhole door and safety-valve; c, ash-pit; d, fire-place; e, flues, the fire going first the whole length under the bottom of the boiler, then back again over the top, and into the chimney; f, brickwork; g, ashes or other convenient non-conductor of heat; the fire-place ends of the boilers were 15 inches lower than the opposite ends, increasing the safety, with less liability to prime, and greater surface for superheating.
"When a boy I was placed as an apprentice or learner with Captain Trevithick, before he left Cornwall for London. On his return to Cornwall, about 1810, he employed me to erect his first high-pressure expansive pole pumping engine at a mine in Gwythian.