Part 4 (1/2)

[3] Also called _ports_

[4] The bores of the cylinders are in the proportion of 4: 6: 9 The stroke of all three is the same

[5] The ends furthest from the eccentric

[6] ”The Locomotive of To-day,” p 87

Chapter III

THE STEAM TURBINE

How a turbine works--The De Laval turbine--The Parsons turbine--Description of the Parsons turbine--The expansive action of steaes of the o Hero of Alexandria produced the first apparatus to which the naiven Its principle was practically the sa dry weather, stea used in the place of water From the top of a closed cauldron rose two vertical pipes, which at their upper ends had short, right-angle bends Between thelobe, pivoted on two short tubes projecting froht tubes Two little L-shaped pipes projected frolobe, at the ends of a dia applied to the cauldron, steah the pivots, and into the globe, fro rapid revolution of the ball In short, the first steah, we have reverted to this primitive type (scientifically developed, of course) in thepractice

HOW A TURBINE WORKS

In reciprocating--that is, cylinder--engines steam is admitted into a chales to expand, it forces out one of the confining walls--that is, the piston--and presently the door opens again, and allows it to escape when it has done its work In Hero's toy the iainst other ed from the pipes was used One may compare the reaction to that exerted by a thrown stone on the thrower If the thrower is standing on skates, the reaction of the stone will cause hilide backwards, just as if he had pushed off from some fixed object In the case of the _reaction_--namely, the Hero-type--turbine the nozzle fro with bodies to which it h fixed nozzles or steaht to bear on the surfaces of movable bodies connected with the shaft

THE DE LAVAL TURBINE

In its earliest form this turbine was a modification of Hero's The wheel was merely a pipe bent in S form, attached at its centre to a hollow vertical shaft supplied with stea-box at one extreentially fro the shaft to revolve rapidly and work the machinery (usually a cream separator) mounted on it This motor proved very suitable for dairy work, but was too wasteful of steah poas needed

[Illustration: FIG 36--The wheel and nozzles of a De Laval turbine]

In the De Laval turbine as now constructed the steaainst vanes36 shows the nozzles and a turbine wheel The wheel is made as a solid disc, to the circumference of which the vanes are dovetailed separately in a single row Each vane is of curved section, the concave side directed towards the nozzles, which, as will be gathered froht of our illustration, gradually expand towards the mouth This is to allow the expansion of the steaain of velocity As it issues, each ainst the concave face of a vane, and, while changing its direction, is robbed of its kinetic energy, which passes to the wheel To turn onceco the wheel with an enorh-pressure steaures, if it enters the small end of a De Laval nozzle at 200 lbs per square inch, it will leave the big end at a velocity of 48 miles per _ht round the world in 8-1/2 hours!

The wheel itself would not move at more than about one-third of this speed as a maximum[7] But even so, it may make as many as 30,000 revolutions per minute Afrom vibration No matter how carefully the turbine wheel may be balanced, it is practically iravity coincide exactly with the central point of the shaft; in other words, the wheel will be a bit--perhaps only a tiny fraction of an ounce--heavier on one side than the other This want of truth causes vibration, which, at the high speed s in which it revolves to pieces, if--and this is the point--those bearings were close to the wheel M de Laval s to ”whip,” or bend a little, and the difficulty was surmounted

The nor of so To dynamos, pumps, and air-fans it is often coupled direct

THE PARSONS TURBINE

At the grand naval review held in 1897 in honour of Queen Victoria's diahts was the little _Turbinia_ of 44-1/2 tons burthen, which darted about a that of the fastest ”destroyer” Inside the ni 2,000 horse poithout any of the clank and vibration which usually reigns in the engine-rooh-speed vessel The _Turbinia_ was the first turbine-driven boat, and as such, even apart froreat attention Since 1897 the Parsons turbine has been installed onseveral men-of-war, and it seems probable that the tiines will be abandoned on all high-speed craft

DESCRIPTION OF THE PARSONS TURBINE

[Illustration: FIG 37--Section of a Parsons turbine]

The essential parts of a Parsons turbine are:--(1) The shaft, on which isinside which the dru; (5) the balance pistons Fig 37 shows a diagrammatic turbine in section The drues, D1, D2, D3, towards the right From end to end it is studded with little vanes, M M, set in parallel rings s 38), the hollow side facing towards the left

The vanes stick out from the drum like short spokes, and their outer ends al To the latter are attached equally-spaced rings of fixed vanes, F F, pointing inwards towards the dru vanes Their concave sides also face towards the left, but, as seen in Fig 38, their line of curve lies the reverse way to that of M M Steah the vanes towards the outlet at B It meets the first row of fixed vanes, and has its path so deflected that it strikes the ring of le, and pushes the of F F, so that it may treat the next row of M M in a similar fashi+on

[Illustration: FIG 38--Blades or vanes of a Parsons turbine]