Construction of Engine : The names adopted for the three principal working parts are as follows : The intermediate vibrating disk P is called the piston, and the sectors /I and A on the ends of the main and dummy shafts are called respectively the main and dummy blades. Tne piston, replacing the geometrical disk of infinitesimal thickness, has to be made of sub stantial thickness, and fitted effectively with a steam-tight packing all round its edge. The hinge union along the straight edge of each blade has to be made a cylinder of finite diameter instead of a geometrical line ; and the junction must be so contrived as to make a substantial hinge-joint that will stand the wear and tear consequent on the rapid oscillation of the parts.
Thickness is obtained for the piston by deducting hlfa its thickness from each of the two fiat sides of each blade—that is, the disk P and sector B. originally depicted as in Figs. 5 and 6, are altered to the forms shown in Figs. 7 and 8. Two cylindrical ribs, having their axes in the middle plane of the piston, are formed on its opposite faces, and along diameters at right angles to each other, Fig. 7, and into these are let circular lugs with eyes, formed on the straight edges of the two blades, Fig. 8, which are thereby hinged to the piston in the manner of an ordinary hinge, having a lug and socket with a pin through. The effect of these depart ures from the elementary geometrical form already described is to reduce the capacity of the engine by the amount of the cubic measurement of the hinges. An external view of the engine is shown in Fig. O. The engine is used for the direct driving of dynamos. and runs from 600 to 1,100 revolutions per min. A test of a 10-in, engine running 600 revolutions per rain. gave a water consumption of 37 lbs. per brake ho•se-power per hour.
Compound Steam Turbine.—Mr. Charles A. Parsons describes, in the Proc. Inst. Al, E., October, 1888, a compound steam turbine of his invention, as follows : The compound steam turbine T (Figs. 10 and 11) consists of two series of pa•allel-flow or Jonval turbines, set one after the other on the same spindle S. so that each turbine takes steam from the one before and passes it on to the one following. In this way the steam entering all round the spindle fronuthe central inlet I. Fig;. 10. passes right and left through the whole of eaeh series of tur bines to the exhaust E at each end. The steam expands as it loses pressure at each turbine; and by successive steps the turbines are increased in size or area of passage-way, so as to accommodate the increase of volume, and to maintain a suitable distribution of pressure and velocity throughout the whole series of turbines. The areas of the successive turbines are so
arranged that the velocity of the flow of steam shall bear throughout the series about the same ratio to the speed of the blades; and as far as possible this ratio of velocity is so fixed as to give each turbine of the series its maximum efficiency. The two equal series of turbines on each side of the central steam-inlet I balance each other as regards any end pressure on the spindle of the motor, and thus remove any tendency to undue wear on the collars of the bearings B. The turbines are constructed of alternate revolving and stationary rings of blades. The revolving blades r, Fig. 12, are cut with right or left hand obliquity on the out side of a series of brass rings, which are threaded upon the horizontal steel driving-spindle s, and secured upon it by feathers ; the end rings form nuts, which are screwed upon the spindle and hold the rest of the rings upon it. The stationary or guide blades g are cut with opposite obliquity on the inside of another series of larger brass rings, which are cut in halves, and are held in the top and bottom halves of the cylindrical casing by feathers. The set of blades on each revolving ring runs between a pair of sets of the stationary or guide blades. The passage between the blades in the alternating rings form a longitudinal series of zigzag channels when the machine is standing still.
A 50-horse-power turbo-generator has been constructed of the triple-expansion type, using turbines of three different diameters. Including fluid friction, the theoretical efficiency of each turbine in the set is claimed to be about per cent ; and the mean efficiency of the whole set is theoretically about 87 per cent of the power which should he given out in the adiabatic expansion of the steam. As the result of tests made when exhausting into the atmosphere and giving off 32, 000 watts, it is also stated that the consumption of steam per electrical horse-power per hour has been found to be 42 lbs., with a steam - pressure of 01 lbs. at the inlet. A 0-horse power generator has run for four years at a speed of 18,000 revolutions per min.