704 



STEAM-ENGINE 



The water for condensing the Rteam is introduced 

 into it in a jet in such n way that ita particles mix 

 with the steam at once on entering, and condense 

 it almost instantaneously. 



The gpverniir, shown in fig. 5, is an ingenious 

 application by Watt of mechanism long used in 

 water-mills. Its object is to make the engine to 



a great extent 

 regulate its own 

 speed, so that it 

 Khali neither be 

 pulled up alto- 

 gether by a 

 sudden increase 

 of load, nor 

 'race 'when any 

 part of its load 



Fig. 5. 



siste essentially 

 of a spindle or 

 upright rod, 

 with a pulley 

 by which it is 



caused to revolve fixed on it. Two levers are 

 pivoted on a pin near the top of the spindle, and 

 HI the lower end of each is fixed a heavy cast-iron 

 ball. When the engine is running at its proper 

 speed the balls revolve with the spindle in the 

 position shown ; but if that speed In- increased the 

 centrifugal force causes them to fly outward, and 

 consequently upward ; and conversely, if it be 

 decreased they fall downward towards the centre. 

 At the upper end of the spindle is a system of 

 levers, by which it will be seen that the raising 

 of the la!l> tends to close, and their lowering to 

 open, the throttlf-ralve at the right of the engrav- 

 ing. The valve in the figure is simply a disc of metal 

 placed in the steam-pipe near the cylinder, but a 

 great many other types of valve more expensive 

 but more efficient are now used for the same pur- 

 pose. The further this valve is opened the greater 

 the amount of steam admitted to the cylinder, and 

 vice versA, and so the tendency of the engine to 

 alter ita speed arising from causes extraneous to 

 itself is just balanced by the alteration made in the 

 amount of steam admitted through the throttle- 

 valve. In order that economy as well as regularity 

 of working may l>e attained, it is in many coses 

 necessary that the governor should lie so arranged 

 as to control the 'cut-off" instead of throttling the 

 steam as in the figure. 



The ' Cornish ' engine, so called from the fact 

 that it is principally used in the Cornish mini's, 

 resembles Watts engine in general appearance. 

 Like Newconien's engine it is used exclusively for 

 pumping and has no rotary motion, and it is virtu- 

 ally single-acting; hut, unlike his, the steam-pres- 

 sure and not that of the atmosphere actually does 

 the work. Cornish engines are fairly economical 

 of steam, but are very costly and extremely heavy 

 ami unwieldy. 



F.nginex in which the piston-rod and connecting- 

 nxl are directly attached are called direct-art i n if 

 engines, of which the horizontal engine shown in 

 fig. 6 is the most common type. For all ordinary 

 purposes direct-acting engines are rapidly super- 

 seding every other form. They possess the merit 

 f having great simplicity mid few working parts, 

 mid <>f nil tln'He parts Ix-ing easily accessible to the 

 <'iigine-driver: and at the same time any required 

 decree of economical working ran lie obtained in 

 tile-in a* well as in any other form. They were 

 at first only used as non-condensing (or so-called 

 ' high pressure') engines, but are now as frequently 

 made with a condenser attached. 



Two other forms of direct-acting engines have 

 ben much used in their day, but are now being 



rapidly abandoned except under special circum- 

 stances ; these are called respectively the ' oscil- 

 lating' and the 'trunk' engine. In the former 

 (which has rarely been used except for marine 

 engines) the crank-shaft is above the cylinder, the 

 piston-rod head is attached to the crank-pin, and 

 the connecting-rod is dispensed with by allowing 

 the cylinder to oscillate on large hollow centres 

 called trunnions, and so to adapt iteelf to the vaii 

 ous positions of the crank-pin. In the ' trunk ' 

 engine the piston-rod becomes a hollow cylinder 

 or trunk, large enough to allow the connecting- 

 rod to vibrate inside it. The latter is then 

 attached at one end to the crank-pin as usual, 

 and at the other to a pin fixed in the piston. 



Fig. 6. 



Direct-acting engines are now made to run at 

 extremely high speeds, for driving dynamos, &c. 

 direct. For this purpose they are made single- 

 acting only, so that the steam-pressure tends al- 

 ways to keep the working surfaces pressed together, 

 and there is none of the shock and noise found in 

 ordinary engines where the direction of pressure is 

 reversed at each stroke. The first successful 

 machine of this type was Mr Brotherhood's ' three- 

 cylinder ' engine, of which an immense number are 

 in use. Of late years Mr Willans, in his ' central 

 valve ' engine, has added an exceptional degree of 

 economy in steam to the other advantages of the 

 single-acting type. Willans' engines are now very 

 commonly usea in the more important electric 

 lighting stations in Britain for the direct driving of 

 dynamos, and have given most satisfactory results. 

 An immense amount of ingenuity has been ex- 

 pended in devising engines in which the rotary 

 motion of the shaft is obtained directly from the 

 piston without the intervention of reciprocating 

 parts. These machines are called rotary engines ; 

 they have never come into general use, and most 

 of them have been defective in construction as well 

 as founded on a dynamical misconception. 



In locomotive engines it is necessary that the 

 whole machinery should be compressed into the 

 smallest possible bulk, and this necessity is tin- 

 cause of their principal peculiarities. The engine 

 itself is much the same as an ordinary hori/.i>nt:d 

 engine, and has two cylinders placed side by side 

 near the front of the locomotive. These cylinders 

 are sometimes placed inside the main framing, 

 which runs the whole length of the engine, and 

 sometimes outside it, eacTi plan having certain 

 advantages. Fig. 7 is an outline section of an 

 ' inside cylinder ' goods-locomotive belonging to 

 the Midland Kailway Company. At the back of 

 the locomotive is the firebox, a, the Ixittom of 

 which is formed by the grate, 6. Fuel is intro- 

 duced by the door. c. The firebox is enclosed in 

 a casing, il, and tlie space between is tilled with 

 water. This space communicates freely with the 

 barrel, e, e, of the boiler, a long wrought iron or steel 



