Thomas Tredgold

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Thomas Tredgold.

Thomas Tredgold (1788 – 1829) was an English engineer and author, known for his early work on railroad construction.


  • Engineering is the art of directing the great sources of power in nature for the use and convenience of man.
    • Thomas Tredgold (1828), used in the Royal Charter of the Institution of Civil Engineers (ICE) published in: The Times, London, article CS102127326, 30 June 1828.

The Steam Engine: Comprising an Account of Its Invention and Progressive Improvement, 1827[edit]

Thomas Tredgold, The Steam Engine: Comprising an Account of Its Invention and Progressive Improvement (1827)

  • In June, 1699, Captain Savery exhibited a model of his engine before the Royal Society, and the experiments he made with it succeeded to their satisfaction. It consisted of a furnace and boiler B: from the latter, two pipes, provided with cocks C, proceeded to two steam vessels S, which had branch pipes from a descending main D, and also to a rising main pipe A: each pair of branch pipes had [check] valves a, b to prevent the descent of the water raised by the condensation or by the force of steam. Only one vessel, S, is shown, the other being immediately behind it. One of the steam vessels being filled with steam, condensation was produced by projecting cold water, from a small cistern E, against the vessel; and into the partial vacuum made by that means, the water, by the pressure of the atmosphere, was forced up the descending main D, from a depth of about twenty feet; and on the steam being let into the vessels again, the valve b closed, and prevented the descent of the water, while the steam having acquired force in the boiler, its pressure caused the water to raise the valve a, and ascend to a height proportional to the excess of the elastic force of the steam above the pressure of the air.
  • The following is a description of the engine, as far as it was improved by Newcomen. B represents the boiler with its furnace for producing steam, and at a small height above the boiler is a steam cylinder, C, of metal, bored to a regular diameter, and closed at the bottom; the top remaining open. A communication is formed, between the boiler and the bottom of the cylinder, by means of a short steam pipe S. The lower aperture of this pipe is shut by the plate p, which is ground flat, so as to apply very accurately to the whole circumference of the orifice. This plate is called the regulator or steam cock, and it turns horizontally on an axis a, which passes through the top of the boiler, and is fitted steam-tight; and has a handle.. to open and shut it.
    Newcomen Engine, Fig. 4 Thomas Tredgold's "The Steam Engine... Invention & Progressive Improvement"
    Newcomen Engine, Fig. 4 Thomas Tredgold's "The Steam Engine... Invention & Progressive Improvement"

    A piston P is fitted to the cylinder, and rendered air-tight by a packing round its edge of soft rope, well filled with tallow, to reduce the friction, and its upper surface is kept covered with water to render it steam-tight. The piston is connected to a rod PA, which is suspended by a chain from the upper extremity D of the arched head of the lever, or working beam, which turns on the gudgeon G. This beam has a similar arched head EF, at its other end, for the pump rod H, which receives the water from the mine. The end of the beam to which the pump rod is attached, is made to exceed the weight and friction of the piston in the steam cylinder; and when the water is drawn from such a depth, that the pump piston is too heavy for this purpose, counterpoise weights must be added at I, till the piston will rise in the steam cylinder at the proper speed. At some height above the top of the cylinder is a cistern L, called the injection cistern, supplied with water from the forcing pump [through pipe] R. From this [cistern] descends the injection pipe M, which enters the cylinder through its bottom, and terminates in one or more small holes at N. This pipe has at O a cock, called the injection cock, fitted with a handle. At the opposite side of the cylinder, a little above its bottom, there is a lateral pipe, turning upwards at the extremity, and provided with a valve at V, called the snifting valve, which has a little dish round it to hold water for keeping it air-tight.
    There proceeds also from the bottom of the cylinder a pipe Q, of which the lower end is turned upwards, and is covered with a valve v; this part is immersed in a cistern of water called the hot well, and the pipe itself is called the eduction pipe. To regulate the strength of the steam in the boiler it is furnished with a safety valve [ sV ]...but not loaded with more than one or two pounds on the square inch.
    The mode of operation... Let the piston be pulled down to the bottom of the steam cylinder, and shut the regulator or steam valve p. ...Apply the fire to the boiler till the steam escapes from the safety valve, and then on opening the steam regulator, the piston will rise by the joint effect of the strength of the steam, and action of the excess of weight on the other end of the beam. When it arrives at the top of the cylinder, close the regulator p, and by turning the injection cock O, admit a jet of cold water, which condenses the steam in the cylinder, forming a partial vacuum, and the piston descends by the pressure of the atmosphere, raising water by the pump rod H from the mine. The air which the steam and the injection water contain is impelled out of the snifting valve V, by the force of descent, and the injection water flows out at the eduction pipe Q; and by repetition of the operations, of alternately admitting steam and injecting water, the work of raising water is effected.

Quotes about Thomas Tredgold[edit]

  • Thomas Tredgold... began to practice as a civil engineer on his own account in 1823, but much of his time was devoted to the preparation of his engineering text-books, which gained a wide reputation. They included Elementary Principles of Carpentry (1820), almost the first book of its kind in English; Practical Treatise on the Strength of Cast Iron and other Metals (1824) ; Principles of Warm- ing and Ventilating Public Buildings (1824); Practical Treatise on Railroads and Carriages (1825); and The Steam Engine (1827).
    • Chisholm, Hugh, ed. (1911). "Tredgold, Thomas". Encyclopædia Britannica. 27 (11th ed.). Cambridge University Press.

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