cylinder has cast with it, or secured, a trunkequal in length to the stroke of the piston, plusthe guide portion and clearance. This trunkis encompassed by a second, formed with orsecured to the piston; and a third trunk ofthe largest size encompasses the piston trunk.It will be understood, therefore, that a clearanceis preserved around the surfaces of the guideand piston trunk, and therefore steam canpass between them to operate on the ends, bywhich means the total area of the piston isexposed to the pressure of the steam. Securedto the piston are two rods above and below thetrunk,—seen in the elevation,—each of whichare connected to a f-piece, which latter isprolonged within the guide trunk. The con-necting rod is attached to the inner, or guideportion of the T-piece, and thus the action ofthe piston is transmitted to the crank pin.The exhaust steam, passage is prolonged to thecentre of the cylinder connection, and thus onesteam-pipe only is requisite. The illustrationunder notice is in connection with the con-denser shown by Fig. 87, in page 260 ; andthe proportions of the cylinder, trunks, &c.,are now introduced :—
Ft. In.
Diameter of Cylinder . . • .47
Length of Stroke of Piston . . .26
Internal Width and Depth of Guide Truuk, 14$ X 16|ins.Width of Space between Trunks . . 0 0|
Length of Connecting Rod . . .59
For direct acting engines the single pistonr od arrangement is the most efficient,—fullye xplained in pages 49, 50, and 51. Theprincipal constructors of the type under noticeare Messrs. Humphrys, Watt, Ravenhill, anda few firms in Scotland .
The elevation and plan shown by Fig. 117is an ordinary design, being very similar to
Fig. 117,
m
C
ORDINARY CYLINDER AND SINGLE ROD PISTON.
that fitted by Messrs. Ravenhill in H.M.S.“ Enterprise,” and not very unlike the practiceof Messrs. Humphrys. The difference in thedesigns by the two firms alluded to consists,that Messrs. Humphrys recess the flange ofthe boring hole, or the stuffing box portion, in-ternally, and the exhaust steam opening is atthe front, instead of the top of the cylinder.Both, and indeed all the firms adopt double-gland stuffing-boxes for the piston rod, asshown in the illustration. A cylinder for apair of engines 160 horse power nominalcollectively, is of the following dimen-sions :—
2 R 2