HYMNS'S' ATIC Puss; HYDRAULIC RAM; POWER TRANSMISSION; PUMPS AND PUMPING MA CHINERY.
Hydraulic
In the hydraulic lifts or elevators, the admission and discharge valves are worked by band at the will of the operator, but in the engines the mechanism Betimes the valves automatically and period ically, thus converting, the lift into a machine with a continuous action. Unlike the vertical water wheels and turbines, the efficiency of which depends upon the weight of a large body of water falling from a comparatively mall height, the water engines work under the pressure of • small column of water descending from a considerable elevation. They are of three types — the "single action,' in which a piston working in a cylinder is moved upward by the pressure of the water, and downward by the weight of the piston it self ; the 'double action,' in which the cylinder is closed at the top as well as at the bottom, and the water admitted to it by supply pipes at those points, acts reciprocally on the piston from above and below; and the 'rotary' in which the water pressure acts on a revolving piston similar to that of a rotary steam-en gine. Rotary engines may be of the single acting or double-acting type, the advantage being with the former, since the pressure of the piston is always exerted on the crank pin in one direction and the dead centres are passed without knocking. Generally three singlas•cting cylinders formed in one •
are used in connection with a disc valve: segmental poets which pass over lag apertures in the valve statism during rotation and the engine will readily start in all positions. The first engine of this kind was constructed by Sir William Armstrong, who also subsequently designed one of the re ciprocating pattern. Since then a great variety of hydraulic engines have bees invented, the greater number of them being of the last name.] type. (See HvaaAtn,tc ENGINE). They have a wide field of usefulness, especially as auxiliary motors for driving small machinery such as hoists,
capstans, crams, %%inches, etc. The employ ment of superheated y .cer motors is one of the lat
tion was based upon the relation of tempera ture and pressure to the vaporization of liquids and the steam was drawn off from its point of formation at the top of the storage tank to the cylinders. Under these conditions, with each revolution the new steam was supplied by water which boiled at continually lower and lower pressures and reduced tempera tures, until the pressure fell to a point at which it was not available for use in the motor; and only about one-ninth of the energy of the heated water was actually used in the cylinders. W. E. Frail of 1% ashington, D. C., suggested the utilization of the power in the storage tank by withdrawing the superheated water directly from the bottom of the tank instead of steam form the top and allowing the water thus withdrawn to expand into steam within the cylinders of the engine it self. In the latest motors, this is accomplished by a generator composed of a nest of tubes coupled into manifolds at the top and bottom. The working pressure is about 700 pounds to the square inch and the water is drawn off from the generator into three insulated storage tanks with a total capacity of 7,000 pounds, carried beneath the car. From the bottom of the tanks the water is delivered through three Tappet valves provided with screw and nut adjustment to regulate the amount of feed. In operation, under the decreasing pressure caused by the movement of the piston through its stroke, the water resolves into steam in a continuous series of flashes, the steam and the unevaporated portion of the water from the high-pressure cylinders passing out through the ports in its bottom and draining off through valves in the lower face of the valve chest. The exhaust steam from the high pressure cylinder passes in the usual way to the low-pressure cylinder and is eventually exhausted into the atmosphere. A car equipped with two compound engines and three tanks charged with water at a pressure of 700 pounds to the square inch and a corresponding temperature of 500* is capable of running 40 miles at a speed of from 30 to 40 miles an hour.
Church, I. P.. 'Hydraulic New York 1911); Gibson, A. It., Ph.
'Hydraulics and Its Applications> (New York 1915); lnnes, C. H., 'Centrifugal Pumps, Turbines and Water Motors' (Manchester, England, 1904).