STEAM ENGINE. 



393 



each lever in connection with the links which move 

 the large slide valve. A wiper, shown enlarged 

 at W, is fixed upon the crank shaft of the engine, 

 and communicates its motions to a rod e, part of 

 which is seen in the fig. and the motions of this rod 

 are carried to the cut off valves by means of the 

 other shafts, rods and levers, also shown in the fig. ; 

 /is the eccentric rod. 



The large slide valve shown above is a modifi- 

 cation of the leech D valve. The pipe h h, which 

 forms the communication betwixt the top and bot- 

 tom parts of the valve, does not work up and down, 

 but it is fixed to the nozles, and the valve slides 

 past it. The eduction pipe h h rests and is pre- 

 vented from rising by means of narrow flanches cast 

 on the top end of it, which are guided by means of 

 similar flanches cast inside of the top part of the 

 nozles ; the construction of these flanches is such as 

 to allow the pipe to be pressed against the valve, 

 although they prevent it from working up or down. 

 As the working part of this valve is very light, it 

 may be made entirely of brass and cast in one piece : 

 behind the rod which connects the top and bottom 

 cut off valves, a light rib is shown in the fig., which 

 connects the top and bottom parts of the large 

 valve. Both faces of a valve, as now described, may 

 be finished in a planing machine. In this sort of 

 valve each set of blocks which press upon the pack- 

 ing should be cut into four pieces ; one of these 

 pieces should press upon each side of the valve and 

 the other two pieces should act upon the packing 

 placed round the eduction pipe. 



In a factory engine, the part of the stroke at 

 which the steam is cut off must be regulated by 

 the governor. The following cut shows a plan of 

 a governor, which shifts the wiper for working the 

 expansion valves, so as to cut off the steam sooner, 



whenever the engine goes too quick, and if the en- 

 gine happens to work below its proper speed, it putt 

 the wiper into a position to give the piston the 

 full pressure of the steam during a longer portion 

 of its stroke ; and in this way the governor keeps 

 the engine going at nearly the same speed, whether 

 it is doing much or little work. The wiper a gives 

 motion to the cut off valves by means of a similar 

 arrangement of rods, levers, &c., as shown in 

 the immediately preceding cut, and it is of the 

 same form as the one shown at W, in the same 

 cut. b is a spur wheel and d is a pinion which 

 gears into it. The part e of the governor is con- 

 nected to the pinion d in such a manner that if 

 the part e rises or falls, it will carry the pinion d, 

 along with it ; but the connection of these parts 

 does not hinder the pinion from revolving on the 

 governor shaft or rod. The wheel and pinion 

 are calculated so as to cause the shaft c upon 

 which the wiper a is fixed, to make the same 

 number of revolutions as the crank shaft of the 

 engine. The pinion d is bored out and fitted to 

 the governor rod, so that it can revolve and work 

 up and down on it, and the feather which forms 

 the connection betwixt the rod and the pinion 

 runs in a spiral direction, as shown in the cut, 

 and not, as in ordinary 

 cases straight up and 

 down. By this arrange- 

 ment, if the pinion d is 

 raised or lowered by 

 means of the governor, 

 the screwed feather will 

 carry it round upon the 

 rod and shift the position 

 of the wiper, so as to cut 

 off the steam sooner or 

 later, according as the 

 balls are up or down, 

 if the screwed feather 

 winds in the proper dir- 

 ection. If the teeth of 

 the spur wheels b and d 

 wind in a spiral direction 

 on the surface of their 

 rims, as in White's wheels, the pinion d, as it rises 

 or falls alongside of the wheel b, will cause the 

 wiper and its shaft to revolve still farther than with 

 the screwed feather, simply if the teeth of the 

 wheel and pinion have the directions as per the 

 angled lines drawn upon them. It will be evident 

 that if the governor was driven at the same speed 

 as the crank shaft, then the shaft c, as well as the 

 wheel b and the pinion d, are not needed ; as in this 

 case, the wiper a would act as before stated, if it 

 was fitted upon the governor rod at the same pla ce 

 and in the same manner as the pinion (/ is fitted. 



Having thus considered the general principles of 

 the structure and action of the steam engine, in its 

 most common forms, we shall next proceed to in- 

 vestigate what may be the amount of mechanic a' 

 energy which it can furnish. 



By reference to the preceding article Steam, it 

 will be seen that, under ordinary circumstances, 

 the steam from a cubic inch of boiling water, at the 

 temperature of 212, occupies one cubic foot ; or, in 

 other words, that the steam fills about 1700 times 

 the space previously occupied by the water from 

 which it was formed. To make this more plain ; 

 suppose that a cubic inch of water were put into a 

 hollow cylinder, whose area is one foot square in 

 the base and twelve inches high, the content of 



