432

MODERN STEAM PRACTICE.

the water through the tubes, flat air vessels are cast along with theend doors, by which the flow of water is rendered smoother and

more equal. The steam entersat the top through an exhaustpipe at each corner, the waterfrom condensation falls downamongst the tubes and is car-ried away by the air pumps;one pump only is fitted toengines of small power, butheavier engines have two airand two circulating pumps.

From the great number ofsuch tubes required to give thenecessary cooling surface, or about 2 square feet per indicated horse-power, the length reaches in large vessels to many miles of tubing;thus in the surface condensers for the new Inman steamer City ofRome, the total length of tubes is about 17 miles.

It appears to be of little consequence whether the water flows in-side or outside of the tubes, so long as a good circulation is kept up.

Sometimes the tubes are arranged independently for eachcylinder, the water from the circulating pump only passing throughthe tubes twice, instead of three times. The pumps are located oneach side of the middle frame, and are worked directly off thepiston of each cylinder. They are of large diameter, one end beingfitted for the circulating pump, and the other end for the air pump;thus for each function this arrangement may be termed a single-action double-acting pump. There is one central chamber andpipe for the suction to the circulating pumps, which first dischargesthe water right and left into a chamber common to both, and thenthrough the tubes; the water returns through the top row, and isdischarged into one central chamber, with one pipe overboard forboth pumps. The arrangement of the valve seats is simple: theyare sometimes placed at the side of the pump, sometimes at the topand bottom. It may be questioned whether single-acting circulatingpumps are preferable to smaller sized double-action pumps. Manyengineers are in favour of the double-action type, but consider, solong as a sufficient quantity of condensing water passes through oramongst the tubes, that a single-acting pump, discharging into acapacious air vessel, makes the flow quite uniform enough for all

A

Fig. 315.—Horizontal Arrangement of Tubes for RettirnConnecting-rod Engines. a, Tube chamber. B, Airpump, c, Circulating pump.