ing lamps, and also power for driving motors, but for the sake of ready reference the following are abstracted. Finally, the following practical list will be found useful. SIZES, POWER, AND COST OF MODERN WINDMILLS. SECTION III. CHAPTER IX. THE POWER OF FALLING WATER. THE use of falling water as a means of motive power is always worth consideration, wherever it exists with reasonable regularity. This is equally true of the motion due to the stream in rivers, and, to a less degree, to that due to tidal action, which, however, suffers in a special degree from intermittency. The movement of water may be utilized in a number of different methods, their comparative values for efficient work being as follows, the theoretical or calculated power of the water being, for the purpose of comparison, taken Hydraulic Ram raising part of water as a pump...... .60 This theoretical or calculated work of the water is ascertained as follows: Cubic feet per minute × 62.4 X the fall in feet 33,000 the work = of the water. Of this result the different machines make more or less effective use as detailed above. So that to get the effective horse-power of any form of wheel, there must be deducted an amount, from 20 to 70 per cent. of the result, according to the motor selected. EXAMPLE.-15 cubic feet per second falling 28 feet, used in a turbine of 70 per cent. efficiency. 15 X 60 = 900 cub. ft. per min. 900 X 62.4 X 28 33,000 47.63 X .70 33.3 effective horse-power. = Quantity. To find the actual quantity of water required by any wheel at any given effective horse-power. The effective horse-power X 528.5 The fall in ft. × the percentage of efficiency given above = actual number of cubic feet necessary. All the text-books give rules in the misleading form of theoretical results. The above rule makes allowance for the loss of work in the wheel or motor. Low falls are sometimes stated in pounds pressure per These are equivalent to heads or falls in feet, square foot. as follows: See, also, an extended table of pressures in lbs. per square inch at end of this section. Measurement of Water Supplies. The following rules and tables are devoted to the subject of measurement of water, both through pipes and in streams, and as these measurements have in many cases to be made by non-technical persons, the methods are fully detailed, and as far as possible the calculations are tabulated. It should be borne in mind that upon the accuracy of these measurements depends the success of installations of water-power, so that care is necessary to record results accurately. |