The steam-cylinder of 1816 was cast in South Wales; the beam still working in the new engine of 1869 was cast in the foundry of the Williams' at Perran. John West replaced the original flat expansive steam-valve with a double-beat valve; the gear was principally made by him on the mine, and remained in good working to the last. This double-beat valve is the first the writer has met with; it is of the same form as the modern double-beat valve; an earlier plan was to have a small valve on the top of the main valve. The steam in ordinary working was shut off when the piston had moved from an eighth to a quarter of its stroke.
The Gons, or Stray Park 63-inch cylinder, survived its companions, the 63 double, and 45 single, for some ten or fifteen years, having beaten both of them in duty. A memorandum in Trevithick's handwriting shows that he in 1798, when designing his large globular boiler with internal flue at the reworking of Dolcoath, tested the relative duty of the Watt 63-inch double and the 63-inch single engine, then called Wheal Gons, the latter in its original form of open-top cylinder atmospheric; shortly after which it probably received a cover about the same time as the 45-inch, for both those engines were thoroughly repaired by Trevithick at the reworking of the mine, twelve or fourteen years prior to the use of the cylindrical boilers.
"At the time that Boulton and Watt made their trial of Seal-hole engine against Hornblower's engine at Tin Croft, the engines were put in the best order, and good coals brought in for the purpose, to work for twenty-four hours. The trial was attended by the principal mining agents; the result was about ten millions by each engine.
"At Dolcoath Mine an old atmospheric engine continued to work for several years by the side of one of Boulton and Watt's engines of the same size; the water lifted and coals consumed were carefully taken and made known to the public, showing that Boulton and Watt's engine performed, when compared with the old engine, as 16 to 10."[83]
Hornblower was an active engineer in Cornwall before Watt; the patent of the latter claiming the sole right of working an engine by steam in the cylinder,[84] drove the former to use two cylinders, in one of which the expansion was carried out, as a means not described in Watt's patent; a lawsuit was the consequence. The two engines when tried by Trevithick[85] performed an equal duty of ten millions. In 1798 he tested the Dolcoath atmospheric 63-inch single against Watt's great 63-inch double action. "The atmospheric performed ten millions," precisely the duty of the patent Watt and the patent Hornblower contests of six years before; but the Watt Dolcoath engine, then considered the best he had made, did sixteen millions. These trials in 1792 and 1798 enable us to compare the Newcomen, the Hornblower, and the Watt engines; shortly after which Trevithick tried higher steam in one or more of those same engines from his globular boiler.[86]
"Camborne, March 10th, 1812.
""Sir Ch. Hawkins,
"Sir,—This day I shall attend the account at Wheal Prosper Mine, in Gwythian, to contract with the adventurers for erecting a steam-engine on my improved plan, for drawing the water 50 fathoms under the adit. I called on Wheal Liberty adventurers at St. Agnes last week, and found that several of them had given up their shares rather than put in a new engine, and the remainder of them very sick.
"I told them that I would fork the water with the present engine, and draw instead of 40 gallons each stroke, 47 fathoms deep (which she did), 85 gallons per stroke, 65 fathoms deep, by altering the engine on the same principle as I have done with the Dolcoath great engine, and several more that are now altering. The expense of altering the engine, and forking the water to bottom, and proving the mine, will not exceed 1000l.
"All the adventurers are very anxious to again resume their shares and make the trial, on condition that I will undertake the completion of the job at a certain sum, but not otherwise.