DETAILS OE SCREW ENGINES.
249
horse power collectively, driving twin-screws,and the proportions of the details under noticeare thus:—
Ft. In.
Number of Discharge Valves, 16.
Diameter of Injection Pipes, 2 . . . 0 2|
Diameter of Discharge Pipe . . .06
Ft. In.
Diameter of Pumps, 2 . . .11
Length of Stroke . . . . . 1 10
Diameter of Pump Eod . . . . 0 21
Diameter of Suction Valves . . 0 6£
Number of ditto ditto, 36.
Diameter of Discharge Valves . . . 0 6£
Number of ditto ditto, 36.
Diameter of Injection Pipes, 2 . . .04
Diameter of Discharge Pipes, 2 . . . 1 3 J
If not in design, certainly in arrangement,the illustration depicted by Fig. 78 forms a
Fig. 78.
INJECTION CONDENSE!! FOB DIKECT ACTING ENGINES.
striking similarity to that of Fig. 76. Thesituation of the condenser is the same, also thedischarge chamber, but the injection water isEmitted at the sides—at the back end, ratherthan a central position. Both dischargechambers are connected at the back ends bya passage, and the discharge pipe is connectedto the central opening.
The present example is compiled from a pair°f engines of 60 nominal horse power collec-tively, to which the following dimensions
pertain
Diameter of Pumps, 2 ,
Length of StrokeDiameter of Pump EodDiameter of Suction ValvesNumber of ditto ditto, 16.Diameter of Discharge Valves
Ft. In.. 0 8f. 1 2. 0 1. 0 4
. 0 4
INJECTION CONDENSERS FOR RETURN ACTIONENGINES.
The type of engines, in connection with thecondensers now to be noticed, interfere withthe arrangement of the pumps and valves to aconsiderable extent. The steam piston rodshave to be prolonged at the sides of thecondenser, and the guides must be in closeproximity. Obviously then, the authorities areto be commended for their different produc-tions, each accomplishing the same result bydissension of opinion. As a proof of this, itmust be remembered that each maker dealswith the same evils common with the type ofengine; therefore, no chance for escape orobviation is possible. Now with direct actingand trunk engines, all makers of theseexamples can freely employ the most compactarrangement of condenser, &c., and thus thecylinders can be situated at the least possiblespace apart.
It is current amongst all who have studiedthis matter, that two compartments are essen-tial to produce condensation, such as con-densing and discharge chambers, and that theformer should be above the air pumps, &c.The engineer has, therefore, to consider whichchamber shall be centrally placed in thearrangement, or rather which shall be fore oraft of the connecting and piston rods. Inconjunction with this, attention has to be givento the transverse space required for the valves,and the fact also that the air pumps must beworked by the steam piston is often the causeof much trouble to attain a conclusion.
2 N