OSCILLATING ENGINES.
is that a crosshead is requisite, or additionaldetail, but the shaft can be of less diameterthan when the crank or single motion isadopted. Other facts also are apparent, suchas the reduction of the labour and material forthe shaft; and when the piston rods of thecylinders are connected on the same crankpin, the duplicate eccentric motion is particu-larly available.
The illustration, Fig. 53, is an example oftwin-eccentric motion. The trunk and piston
AIR PRMP, TWIN-ECCENTRICS AND CROSSHEAD MOTION.
a re of the ordinary kind, also the connection°f the rod. The eccentrics are shown in enda nd side elevation, to render their form ob-vious. For an air pump 3 ft. in diameter,and a stroke of 15 in., the following dimensionsare in practice :—
Ft. In.
Diameter of Trunk . . . . 0 11
Length of ditto.2 6|
Distance between Centres of Pin and Cross-
head • . . . . .2 5 %
223
Distance between Centres of Crosshead and
Ft.
In.
Intermediate Shaft .
. .
4
0i
Diameter of Intermediate Shaft
. ,
0
10
Diameter of Crosshead Bod
,
0
3 >-
Diameter of Eccentric Eods
. .
0
n
Diameter of Eccentric
.
2
n
Diameter of Eccentric Bolts
0
Width of Eccentric
0
Width of Eccentric Band
0
31 -
Distance between Centres of Eccentrics
3
n
Depth of Crosshead at Centre .
, .
0
n
Ditto ditto at Ends
, t
0
4
Diameter of Boss at Centre
, ,
0
6i
Ditto ditto at Ends
, ,
0
4£
Thickness of Web at Boss
, ,
0
Thickness of ditto at Eye
•
0
li
In page 203 a notice is made of a
mode of
horizontal motion for air pumps by Messrs.James Watt and Co. : the illustration, Fig. 54—page 224—is a sectional elevation ofthe engines there alluded to. The con-denser and exhaust trunnion pipe are shownin section, the remainder of the engine beingin complete view. The link motion andstarting gear is precisely as that depicted byFig. 46—page 206—therefore needs no com-ment at present. The condenser is fitted with2,407 tubes, each 6 feet long and i inchdiameter. The circulating and air pumps areeach 18 inches in diameter, and the stroke thesame in length. The arm secured on thecylinder gudgeon imparts motion to the rodconnected to each pump, and the slot addedto the rod prevents the vibration curve, orversed sine, affecting the motion. The rods areguided fore and aft of the centre of motionby brackets each 4 inches long, secured, to thelower frames. The arm clasps the rod by adouble eye, the brasses being sustained in theslot, and the connecting pin, 3 inches in dia-meter, is of the usual kind. Each rod is 2Jinches in diameter, and 4 feet 5% inches long,