WHEELS ANCIENT AND MODERN.
(Specially written for FIRE AND WATER.)
FOREIGN engineers, especially those of France, claim that, although American engineers have produced first-class turbines, they have failed to utilize to the best advantage falls of less than two and one-half feet head for draining their wheels. The French engineers claim they can do better than that, and can turn to account falls as slight as four inches. They quote in proof of the fact that at Maquens, near Carcassonne, a “turbinette”—so they style their Lilliputian wheels—working with this slight head of water develops a power of nine kilograms, raising the water to the height of thirtyfivemeters (llSfeet). AtAixen-Savoie, wateris raised to the height of fifty-five meters (180 feet), with an available fall of only twenty-five centimeters (ten inches). At Toulouse, also, a turbine working with a column of fifty centimeters yields a force of fifteen horse power. In order to obtain good results, they say that all that is required is to arrange that the turbine be constantly under water.
The tiret thing necessary in a water power is, of
course, to know what amount of head and fall can be secured and then what quantity of water the stream affords for driving the turbines. This is arrived at by a very simple process of measurement already described in one of the present series of articles (FIRE AND WATER, May 27, 1899, pp. 168, 169). An important matter in measuring small streams is the possibility of damming or holding the water and using it a part of the time instead of constantly. If the water is held for twelve hours and the whole quantity used in the next twelve hours, with the supply that the stream affords in the same time, the power of the stream would be doubled for the twelve hours and would give a better effect than if used constantly.
The next consideration is that of the proper method of setting turbine wheels, such as the Victor and others already described. The Victor, like others, is a flume wheel constructed to rest by the flange of its case or stationary part upon the floor of the flume over an aperture in the floor through which the wateris discharged. Whether the flume is round or square, its internal diameter should be between five
feet, six inches and twenty feet, six inches—based upon a head of twenty feet or less. The size of the wheel should be from twelve inches to forty-eight inches. Across every flume should be provided a rack, to prevent the passing of drift wood and other rubbish into the wheel. The frame of the flume can hardly lie too strong, esi>ecially its lower timbers and floor. The floor timbers should be placed in the direction of the current, with their upper surface low enough to insure the end of the cylinder being submerged at least two inches in standing tail-water when at its lowest stage. The forebay leading to the flume should be of sufficient width and depth to allow the water to pass to the wheel at a velocity never exceeding one and one-half feet per second, and should be free from abrupt turns or cramped passages which break the water into eddies, thereby diminishing its force and reducing the working head. The tail-race should be of the same capacity, and, when practicable, of sufficient depth below the surface of the stream into which it empties, to have at least two feet of dead water standing the entire length of the tail-race when the wheels are not in motion; and, when a large amount of water is to be used on the
wheels, this depth of dead water should be increased to three or four feet. This, being displaced by the water as it is discharged from the wheel, at once conforms to the general level of the water in the tail-race, river, or receiving canal. Thus no head is lost.
To ascertain the requisite size of flumes and tailraces: Given the tables of power, etc. (See above), and the proper size of wheel to produce the required power, and also the number of cubic feet of waterthe wheel will discharge per minute, then divide the number of cubic feet by 85, and the quotient will be the area in square feet required in the cross section of the head or tail-race for every wheel used That is to say—for every eighty-five cubic feet of water used by the wheel or wheels per minute, there should be one square foot in cross section of all the water passages leading to. and from the wheel, including, of course, the opening under the flume, through which the water passes after leaving the wheel. Larger water courses than indicated by the above rules are not objectionable, but desirable; for the nearer a state of rest the water can be brought to before entering and leaving the wheel, the better will be the results obtained.
(To be continued.)