DETAILS OF (PADDLE-WHEEL)
220
Ft.
0
In.
12i
Diameter of Bolts for ditto . . .
0
li
„ of Expansion Rod
0
li
„ of Plunger Rods
0
2
Diameter of First Lever Shaft .
0
2
„ of Valve Spindle
0
1 7
L -$
Length of First Lever (as shown)
0 10£
Length of Second Lever ....
0 10£
Length of Third Lever ....
0
6
Stroke of Eccentric ....
1
li
Stroke of First Lever (as shown)
1
4
Travel of Second
1
1
Travel of Third „
0
4 £
Length of Sliding Space for Adjusting Block
0
8
Diameter of Trunnion Bearing .
1
81
Diameter of Pump Plunger
0
10f
AIR PUMP MOTION AND CONNECTIONS.
The air pumps of oscillating engines usuallyderive their motion from the intermediatecrank shaft. To produce the requisite connec-tion of the shaft and the piston, two meansonly at present are universal, either by cranksor eccentrics. Now with each of these detailsthe principle of motion is alike; the crank pindescribes a circle, and also the centre of forma-tion of the eccentric, during the rotary motion.The air pumps are mostly located angularly, oneach side of the condenser, and the terminationof the angles are at the centre of the shaft.This will be understood by referring to Fig. 45(page 201), the angles of construction beingshown by dotted lines in the “ sectional eleva-tion.” Next to be considered, after determiningthe position of the pumps, is the length of therods. This dimension will, in a great measure,depend on the means adopted for guiding thesliding point of connecting rod. The presentpractice is to use “ trunks,” as shown in Figs.42, 43, and 45, in pages 196, 197, and 201, toguide the sliding point of the rod, locating thepin near the piston. In some instances thepin is midway of the trunk’s length, in order to
reduce the diameter of the trunk ; but, by this,the strain on the latter is, of course, greatlyincreased to that imposed when the pin islower down. It is for this cause that the con-nection is generally adopted, as depicted in theillustrations alluded to. It will also be noticedthat when the piston is at the full up-stroke, thecentre of the pin is below the gland of thestuffing box. Now these marks apply directly tothe preliminary considerations common to the“ air pumps” and mode of working the pistons,and the next step is the form and construction ofthe connecting rod. When two air pumps areused, they are either directly opposite eachother in plan, as in Fig. 42—page 196—or thecentres are apart equal to the width of theconnecting rod bearing, plus the clearance. Thearrangement illustrated requires only one con-nection with the crank pin. One rod is keyedinto the lower portion of the brass, and theother is hung on a pin on the opposite side.The keyed rod always forms a direct line fromthe centre of the crank pin, but the oppositerod a broken line at the point of suspen-sion at certain portions of the stroke. This
Fig. 51.
will be better understood by alluding to Fig. 51,