258

DETAILS OF SCREW ENGINES.

great enquiry as to the cause for this, particu-larly so on remembering that the steam itselfis not a pure vapour, and that it is impreg-nated in the cylinder with the tallow, &c.,although super-lieating to a great extent miti-gates the evil. The outer rows of the tubesmay present a clean appearance, while thosecentral are coated with refuse, and thususeless as conductors. To inspect the latter,the removal of the former is imperative, andtherefore disarrangement the result. Nowwhere the steam passes through the tubes, therefuse, of course, accumulate on the innersurface, and the removal of the coating isreadily effected by a brush or suitable scraper.Each tube can thus be treated, and the cer-tainty of cleansing the result.

The tube plates of a condenser always re-ceive a portion of the solid matter left by thesteam, and when the process of condensationis between the plates, inspection, even, is im-possible without the removal of the tubes.

By the internal circuit now advocated, theplates are the first and last surfaces in con-tact, and thus the removal of any accumula-tion—to say nothing of inspection—is an easyprocess.

The modern practice by some of the leadingfirms of the day is to cause the steam to passthrough an inclined set of tubes. The cir-culating water enters the chamber at a certainlocality, and the discharge opening is oppo-site. In some instances a pipe is introduced■—perforated—under the tubes, and thus thewater is more effectually distributed.

To enable a just and practical opinion as tothe present practice, attention is now directedto the various arrangements.

SURFACE CONDENSERS FOR DIRECT ACTINGENGINES.

In common with the description relatingto injection condensers, the present sectioncommences with the details under notice,especially adapted for direct acting engines.

The firm of Messrs. J. Penn and Son haveconstructed and fitted in H.M.S. “ Arethusa”the arrangement of condensers shown by

Fig. 85.

MESSES. PEHN S SUBFACE CONDENSES FOE DIEECT ACTINGENGINES.

Fig. 85—also shown in sectional plan andcomplete view in Plate 27.

The tubes are horizontallv arranged abovethe pumps, the steam surrounding them withinthe compartment, the pumps being near thecentre of the arrangement. The suctionvalves are below the barrel, at the side, andthose ior the discharge are directly above.The passage for the circulating water is thus.On the water entering at the central backopening, it is forced—by the pump’s piston—through the central end of the first tier oftubes, and.on reaching the opposite extremityit rises arid enters the top set, the final dis-charge being through the upper openingthe back end of the structure.

The exhaust steam enters the compartment