277
tlie firms who advocate the arrangement,Messrs. Randolph and Elder occupy a promi-nent position. Messrs. Dudgeon have latelyput forth their knowledge on the subject, of
Fig. 120 .
Messrs, dudgeon’s compound cylinder with three
l PISTON RODS.
Vrhich the illustration, Fig. 120, is a good ex-ample. This is two cylinders, one within theother, and steam ports and passages to corre-spond, as shown in the sectional plan. Threepiston rods are requisite, and an annular pistonbesides the one central. The piston rods areOn the horizontal line—being for a directActing engine—the glands are of the ordinaryboini, adjusted by nuts and bolts. The smalleroylinder is secured at the front end only, theback extremity being recessed in the backoover of the larger cylinder. Messrs. Dud-goon’s practice for engines, on the compound
system, B50 horse power nominal collectively,for twin screw propulsion with four cylinders,is as follows:—-
Diameter of Low Pressure Cylinder .
Ft.
. 5
In.
2
Ditto High ditto ditto
. 2
8
Length of Stroke ....
. 2
0
Diameter of Low Pressure Piston Rods
. 0
41
Ditto High ditto ditto Rod
. 0
Q 7
Depth of Piston ....
. 0
8
STEAM PISTONS.
The principles to be observed in connectionwith the details under notice are expressed inpage 228, and an illustration of the gasketpacking is shown by Fig. 59, in page 229.An example of a nearly similar mode of pack-ing is shown by Fig. 121, being a sectional
Fig. 121 .
DUPLICATE MODE OF CONNECTING PISTON KING.
plan. The ring is divided, and the space filledby arecessed plate secured only at one extremity—to admit expansion and contraction. Toprevent a collapse at the division, a secondplate is introduced of a greater length, andthus the uniform curve is preserved. Thetransverse section, shown by Fig , 122, in page278, illustrates the face ring, and the securingand stop studs, also the depths of the pistonand ring.
The adoption of springs behind the pistonring is now becoming general, and more par-ticularly where high pressure or super-heatedsteam is used. An illustration of the applica-tion of springs is represented by Fig. 123 for