LOCOMOTIVE ENGINE. 
427 
fitting in a spiral groove on the spindle, similar to a screw; only that the groove 
makes but a quarter of a turn round the spindle, and is very much inclined to it, 
so as to cause the valve to be sufficiently drawn back by a quarter turn of the 
handle. This regulator is very efficient, and acts a little more uniformly than the 
other, but the friction in it is greater from the spiral motion, and it is more liable 
than the other to get out of order and stick fast. 
Steam Chests.—The steam chests or slide valve boxes U U, (Plates XC., XCI., and 
fig. 4, Plate XCII.,) are made of cast iron half an inch thick; and are bolted down upon 
the top of each cylinder, and to the front plate of the smoke box, in which holes are cut 
of the same size as the steam chests, and closed by cast iron plates termed bonnets 
bolted on the outside. The steam chests have the two branches of the steam pipe 
fixed upon them at the back, and opening into them; and a stuffing box, is cast upon 
the end of each, passing through the tube plate n, the joints being completely and 
firmly closed by running melted lead into it all round. 
Slide Valves.—In the steam chests are placed the slide valves, V V, shown in section 
longitudinally and across in Plate XC., and fig. 4, Plate XCII. They are brass boxes 
1-| inch deep inside and three eighths of an inch thick, having flanches five eighths of 
an inch thick all round them at the bottom. The slide valves are made to move 
backwards and forwards by the spindles which have each a cross piece at the end 
that fits into a notch in the back of the valve; the spindle is generally connected to 
the valve by means of a rectangular wrought iron frame, called a bridle, dropped 
over the valve and having the spindle screwed into it. The bridle has an advan 
tage in holding the valve very steady, and yet allowing it to drop through readily 
as it is worn by friction, and thus keep always in contact with the surface that 
it slides upon. The valve spindle t moves steam-tight through the stuffing box k' at 
the inner end of the steam chest. 
Cylinders and Piston.—The cylinders, H H, where motion is produced by 
the pressure of the steam, are made of cast iron, five eighths of an inch thick 
and 12 inches diameter inside, and aro bored out perfectly smooth and cylindrical. 
A box is cast on the top of each cylinder, running along its whole length and flat 
on the upper side, containing two hollow rectangular passages m\ ri, and another 
passage o', between them; these are separated from each other, and the ends 
of them are shown coming to the outside and opening into the steam chest at the 
leit cylinder, (Plate XCI.) The two outer passages n, are the steam ports; they 
are eight inches long and one inch wide, and open one into each extremity of the 
cylinder, for the purpose of conveying steam to and from the cylinders; their area 
is 8 square inches, or rather less than the area of the steam pipes. The other pas 
sage o', is the waste steam port, of the same length, and one inch and a half wide on the 
face; expanding inside, as shown in Plate XC., occupying all the space between the