Pooly also saw the finishing stroke in 1811, when the boilers still known as the Trevithick or Cornish boilers, gave steam to the three engines; after a twelve years' fight between low and high pressure, commencing with Trevithick's globular boiler and internal tube, in Dolcoath, in the year 1799, from which time it gained step by step, though in comparatively small engines, up to 1811, when the cylindrical boilers took the place of the condemned hearse and globular boilers, and gave really strong and expansive steam to the three Dolcoath pumping engines that from time immemorial had been rivals, causing all three of them to lift an increased quantity of water, and at the same time to save one-half in the cost of coal; this continued for four or five years, when in 1816 the 63-inch double and the 45-inch, being the youngest and the oldest of the three, were removed, that a new 76-inch cylinder, better adapted to Trevithick's expansive steam might more cheaply perform their joint work. Prior to this change the three engines were known by the names Shammal 45-inch, formerly Bullan Garden,[79] but before that as Carloose, of the period and form of the Pool engine;[80] Stray Park 63 single, formerly Wheal Gons,[81] dated from 1770 to 1777; and the 63-inch double of Watt in 1780.
"Dolcoath Mine, March 29th, 1858.
"Sir,
"I have obtained the following information respecting the building of the first cylindrical boilers, as ordered by your late father for Dolcoath; and some information of the results as to the coals consumed, compared with the consumption by the boilers previously in use here.
"George Row, now about seventy-two years old, and working at Camborne Vean Mine, says he assisted to build the two first cylindrical boilers with internal tubes used in Cornwall. They were built in Dolcoath Mine in the year 1811; they were 18 feet long, 5 feet diameter, having an oval tube 3 feet 4 inches in the largest diameter at the fire end; the other or chimney end of the tube was somewhat smaller. They were found too small for the work to be done, and another boiler was built immediately, 22 feet long, 6 feet 2 inches diameter, and he believed a 4-feet tube.
"John Bryant, now seventy-four years old, works a steam-engine at West Wheal Francis. He worked at Dolcoath the 63-inch cylinder double-acting engine, upon Boulton and Watt's plan. When he first worked her she had the old bee-but boiler, 24 feet in diameter. They were taken out for the Boulton and Watt waggon boiler, 22 feet long and 8 feet wide, with two fire-doors opposite one another.
"Then the Boulton and Watt waggon was taken out for Captain Trevithick's boilers, which he worked for several years. Two boilers were put in, each 18 feet long, 5 feet diameter, with an internal oval tube, he thinks, 3 feet by 2 feet 6 inches. Shortly after, another boiler of similar form was added, 22 feet long, 6 feet diameter, 4-feet tube.
"He cannot say what the saving of coal was, but remembers that the duty performed by the engine with the waggon boiler was thirteen to fourteen millions. Mr. William West came to the mine as an engineer, and by paying great attention increased the duty of the Boulton and Watt engine and boiler to about fifteen millions. He does not recollect the duty the engine performed with the cylindrical boilers.
"Mr. Thomas Lean, of Praze, the present reporter of mine engines in the western part of Cornwall, in answer to a note I sent to him, says he has no account of any report of Dolcoath engines for the year 1812, but during the month of April in that year the engines did 21½ millions. During the whole of 1813 that engine was reported to average a duty of twenty-one millions. The whole of the above are at per bushel of 93 lbs., and the whole of the accounts furnished by Mr. Lean are for Trevithick's cylindrical boilers.
"From the Dolcoath Mine books I find the following: Paid for coals for the whole mine during the year 1811, 1150l. 15s. 10d., or per month, 931l. 14s. 7d. During the first three months of 1812 the coal averaged 1000l. per month. In May of this year, 1812, Captain Trevithick is entered on the books as paid 40l. on account of boilers; and in August of the same year, for erecting three boilers, 105l. I think the three boilers were at work in April, 1812, the month Mr. Lean gives as the first reported. From April, 1812, to December, during nine months, the cost of coals was 5512l. 6s., averaging 612l. 9s. 6d. per month. During the next year, 1813, the cost for coal was 7019l. 17s. 5d., or an average per month of 590l. 16s. 5d. I cannot find the price paid per ton for the coal in these years, but the average price during 1808 and 1815 was much alike, making it probable that the price per ton during 1811, 1812, and 1813, was nearly the same; and that the saving of the above 300l. per month in Dolcoath was wholly on account of the saving effected by Trevithick's cylindrical boilers.