200 DETAILS OF (PADDLE-WHEEL)

case matters are reversed, the valves, commonto the condenser, open only to drain the same,when the piston is descending; after this isaccomplished the water is discharged withoutpassing through the piston; thus finally thesame result ensues, the water is dischargedwhen the piston is ascending—as before—butthe foot valves are closed. Further than thisas an actual gain, the gravity of the waterassists the action of the pump when drainingthe condenser. By this arrangement a bettervacuum is certain, and one entire set of pistonvalves dispensed with. Economy of materialis thus produced, simplicity of arrangementeffected, and the main attainment—perfectcondensation—rendered certain. This ar-rangement under direct notice is originatedby ourselves.

For a pair of oscillating engines of 150horse power nominal collectively, havingone air pump, the following are the di-

mensions :—

Ft. In.

Diameter of Connecting and Piston Hods . 0 4

Diameter of Air Pump . . . . 2 10

Length of Stroke . . . . .20

Area of Suction Valves (10) . . 260 sq.in.

Area of Discharge Valves (12) . . 280 sq.in.

Diameter of Injection Pipe . . 0 4f

Thus far the injection condenser has beendescribed and illustrated according to thegeneral practice of the present day. Itbecomes next necessary, before closing thepresent section, in doing justice to the detailsunder notice, to allude to the surface con-densers as applied to oscillating enginesadapted for paddle propulsion. The systemof condensation now adverted to is not asuniversal as the injection kind; due, perhaps,

more to the numerous details requisite, andthe motion required for the pumps, than anyother cause, as the latter acquisition is in factthe main attainment to be overcome. Withsurface condensers two classes of pumps arerequisite, one for the exhaustion of the con-densed steam, and the other for the circulationof the condensing water. Now, with oscillat-ing engines, two means of imparting motionto these pumps are only available withoutauxiliary power; either from the vibratoryaction of the cylinder, or from the rotativemovement of the crank shaft. Having thusdecided the means available for the givenpurposes, it will be well next to consider thepracticability in either case, and decide as tothe better mode. The arrangement of the con-denser at present need not he attended to, butimmediate allusion being given to the pumps.Now if the motion is imparted direct fromthe intermediate shaft—whether by crankor eccentric—the pumps will have a verticalaction in principle, although they may besituated angularly.

By the introduction of levers, a horizontalmovement for the pistons can be producedfrom the crank shaft. If this latter actionis required to be directly derived, thelower end of the cylinder will impart themotion, or by a projecting arm from theupper portion of the cylinder, a verticalaction can be given to the pump. It willthus he understood that various means ofconnection are available, each having ftdistinct relation to the working parts of theengines. Now, if a vertical action is resortedto, the pumps and valves must be beyond thecondenser at the front or sides, thus occupying