HYDRAULIC TRANSMISSION OF of power for lifting, etc., by water under pressure is in common use in steel works and other large manufactories, but it is not generally adopted for long distances, transmission by compressed air, by steam-pipes, or by electricity being usually preferred. It is, however, a valuable system for districts in cities where there is much lifting to be done, as in warehouses. The most extensive application of this system is that made by the London Hydraulic Power Co. Over 50 miles of hydraulic mains have been laid in London, embracing nearly the whole city, NVestminster, and Southwark. The mains laid in the street are from 7 in. internal diameter to 2 in. They are chiefly of cast-iron with flanged joints and packing rings of gutta-percha. The mains are kept charged by powerful pumping engines. The reservoirs of power consist of capacious accannulators, loaded to give a pressure of 750 lbs. per sq. in.. producing the same effect as if large supply-tanks were placed at 1,700 ft. above the street-level. The water used is pumped direct from the river. The hydraulic power is supplied direct to elevators, presses, and fire hydrants and other apparatus of similar character, without the use of any engine or power-producing machinery, but the hydraulic pressure can also be used for driving engines of special construction in the same way as steam or gas. Hydraulic engines worked from the company's mains are now used for all sorts of purposes, such as coffee-grinding, ventilating. working elevators and crushers, driving dynamos and general machinery. The hydraulic power is also used for pumping water from deep wells or from the basement of a building to a tank on the roof, or for the drainage of cellars, and for supplementing the deficiency of pressure from the water-works mains.
A valuable paper on waste of power in hydraulic transmission, by Mr. It. G. Blaine, will be found in Engineering, Nay 22, 1891. 3Ir. Blaine deduces the formula, in which L = length of pipe in feet ; d = diameter in feet; horse-power sent into pipe at one end, and p = equals pressure at entrance in pounds per square inch. Values of the coefficient •6367 ;I, for diameters in. to 12 in. are as follows: Erample.—If 100 horse-power are sent into a straight pipe one mile long and 6 ins, in diameter, the entering pressure being 700 lbs. per sq. in., find the power wasted in trans mission.
here ere -00369 x 5280 x 11' 700' x (•5)6 = 1.82 horse-power.
This method shows how to calculate the power wasted in friction in straight pipes of any hydraulic system. There are, however, certain other sources of loss, such as bends in the pipe, roughness of its inner surface, etc., which cannot well be taken into account, making the result less favorable in regard to the efficiency of the system. In connection with the
energy wasted at bends, the reader is referred to W'eisbach's Hydranlies, or to the article by Professor Unwin on - Ilydroineeganies " in the Encyclopedia Britannica. Mr. Blaine. in Engineering, June 5, 1891, has, with the above met hod as a basis, worked out a method of calculating the most economical diameter of pipe for a given horse-power and distance, and compared the efficiency with that of electric transmission under certain specified conditions.
The Distribution of Heat and Power by Hot Water will be found described in a paper by Mr. A. V. Abbott, Trans. Am. Inst. Shining Engrs., February, 1888. This system was tried in Boston, but not successfully. Water was delivered to the customers at a temperature of F.. corresponding to 250 lbs. absolute pressure to the square inch. It is not improbable that with improvements in certain details and situations, this system may prove of value and importance.
Transmission of Power through a nre1171111.—This system, as practiced in Paris by MM. Petit and Boutlenott, consists in maintaining, by means of exhausting engines working at a central station, a reduced pressure in the mains to the amount of as nearly as possible two thirds of a perfect vacuum. Service pipes from the mains pass into the premises of the users, and are connected with the motors; and work is thus performed by the difference in pressure between the atmosphere and the vacuum in the mains. The exhausting engines do not ex haust direct from the mains, but from a reservoir serving to some extent as a regulator, from which the mains are laid either under the streets or in the subways; and the motors are started or stopped by simply opening or closing a valve on the There are three exhausting engines of about 90 horse-power each: one of them is independent, while the other two can be coupled together. The steam cylinder is 13 in_ diameter and 42 in. stroke, and works with a boiler pressure of 85 lbs. per sq. in. The exhausting cylinder of 41 in. diameter is in the same line with the steam cylinder, both pistons being on the same rod. Pressure regulators, indicators, and counters, record continuously the vacuum in the mains and the revolutions made by the engines, whereby a check is obtained upon the amount of power supplied. The motors are made in three sizes, of k horse-power, 1 horse power, and 14 horse-power; the last seems to be the maximum that can be worked with advantage, and where more power is required it is obtained by coupling two motors together. The present length of the exhaust mains from the central station is about a thousand yards.
Press : see Book-binding Machines, Glass-making, Mills, Silver, and Wheel-making Machines.