SCREW ENGINES.

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with differently arranged condensers andmode of working the pumps, &c., to whichallusion will now be made. When the con-densers form the structure for supporting thecylinders, the former is at the extremities ofthe arrangement, or fore and aft. The airpumps—sometimes two to each engine—aresecured to that side of the condenser, facingthe centre line longitudinally. The valvesare within the condenser and the doors foraccess are at the outer side. The feed andbilge pumps are secured to the lowerframing. All the pumps are worked directfrom the steam piston, thus dispensing withlevers, &c. The slide valves are eithersituated at the extremities, or between thecylinders, the former position being mostlyadopted. The guide blocks for the pistonrods are the slipper kind. The guides are atthe side most effective to resist the line ofstrain of the connecting rods, due to the direc-tion of the crank’s rotation. Other arrange-ments consist of the condenser being situatedas the last, but the pumps worked by leversas before described. This latter mode is,perhaps, the preferable for access for repairs,but not for economy.

Surface condensers do not materially affectthe position of the pumps in relation to thosefor the injection kind; the difference beingchiefly an additional pump for circulation.The last arrangement is common to bothinjection and surface condensers: by con-tinuing the latter on one side, for the entirelength of the arrangement, in order to attainthe tubular surface requisite.

In another example—the side frames areadopted, and the tube compartment, situated

between the same, transversely of the hull ofthe vessel, or centrally of the engines. Therequisite pumps are on each side of the con-denser ; motion being imparted to the formerby levers. These latter - are fixed at one endto a shaft or pin, the other extremity isattached to the crosshead of the steam pistonrod, in the ordinary manner; and thus areduced length of stroke is given to thepumps.

In some cases the pumps are of a combinedarrangement ; i.e., one side of the piston cir-culates the water, while the opposite drawsthe condensed steam, at each stroke.

With a third classification, the condensersupports the cylinders centrally, the outer sidesbeing sustained by wrought-iron stays. Therequisite pumps are of vertical action placedbelow the condenser. Motion is attained by along cross head secured to the steam pistonrod—one or two being used—thus a directconnection is produced; with the advantageof a single guide being equivalent to rods,levers, links, &c. Another gain in this centralposition is, the correct distribution of themachinery in the hull, a matter worthy of dueconsideration. In order to reduce the longi-tudinal length of the arrangement—in propor-tion to the last example, the condensers areone to each engine, separately situated oneach side of the same. Motion is imparted tothe pumps as in the last example. Thepumps are double acting, separately arrangedin alternate positions on each side of the con-densers. By this arrangement it can bereadily understood that the access to all therequisite parts is effected with a certainty,without cramped room or discomfort. With re-