GIOVANNI BRANCA’S STEAM ENGINE (1629).
The simplest form of Turbine.
From the Exhibit in the Victoria and Albert Museum.
Steam was to be raised as usual, by applying heat to a vessel containing water. (In the picture this vessel is seen to be in the shape of a man’s head and neck, the steam, so soon as it is formed, issuing out of his mouth. The original illustration was published in Le Machine by Giovanni Branca, printed in 1629, and containing all sorts of most interesting labour-saving devices, such as the employment of winches, chain-pumps, water-wheels, water-buckets and pumps of many kinds.) As the steam escaped it was directed against the vanes on the circumference of a wheel fitted with little fans like a water-wheel, and so causing it to revolve. In the picture the wheel is being utilised by means of gearing for lifting pestles. Speaking generally, this resembles roughly the idea of the de Laval turbine, but in actual application de Laval allows the steam to issue through one or more nozzles placed as close as one-sixteenth of an inch to the blades or fans, so that every particle of steam shall strike a blade.
THE BLADES OF A PARSONS TURBINE.
By permission of Messrs. C. A. Parsons & Co., Newcastle-on-Tyne.
But the Parsons system differs in detail from this, and employs a number of wheels mounted on the same shaft, the steam entering at one end, working its way along and expending its energy to each wheel as it passes. If the reader will examine [the illustration facing page 186], he will see a section of one of these turbines, which is here reproduced through the courtesy of Messrs. C. A. Parsons and Co. But before we deal with the actual working of this, we would also call attention to [the drawings on page 185], which depict alternate rows of fixed and moving blades. Steam enters the turbine in a direction parallel with the axis of the shaft, and flows through the length of the turbine in a zig-zag fashion. Looking at the top line in this diagram, we see a row of fixed discs or blades sloping in one direction, on to which the steam pours. These, so to speak, reflect the steam so that it passes at right angles from the slope of the fixed blade to the first row of moving blades which are on the shaft, thus giving them and it a rotational force in the direction indicated by the arrow. But the curved shape of the moving blades causes the steam to issue from them in a direction exactly opposite to that in which it had entered, and thus the reaction gives additional rotational force to these moving blades. The steam now reaches the next row of fixed blades and repeats the same action again on the next row of moving blades.
