204 DETAILS OE (PADDLE-WHEEL)

acting air and circulating pumps under them.The motion for the pumps is derived from armssecured to the trunnions or gudgeons of thesteam cylinders.

Messrs. Ravenhill and Hodgson have latelyrepaired the S.S. “ Ripon,” of good repute, andintroduced surface condensers in the wings ofthe engine room. The air pumps are eachworked by eccentrics, and the water is forcedthrough the condensers by separate centrifugalpumps; the motion for these pumps beingderived from the crank shaft by mitred gearingon it, and at each extremity of the countershafts and pump spindles.

There are other means proposed to obtain avertical action for the pistons of the pumps inquestion, and dispensing at the same timewith the cranks or eccentrics on the interme-diate shaft, viz., by projecting arms on theupper portions of the cylinders. This ideahas been patented by Messrs. Davison andPaterson, and described in their specificationthus, in 1861 :—

“ In the case of oscillating engines, the airpumps and circulating pumps are worked bythe motion ot the cylinder. The pumps areworked by means of arms or levers attachedto the cylinder; and to sustain the strainarising from thus working the pump, guidesare attached to the cylinder cover, betweenwhich the piston rod slide block works, orthe piston rod may be otherwise suitablyguided. In some cases we arrange a supple-mentary pump, in connection with the valvesand passages of the circulating pump, withprovisions for working it by auxiliary power,,j for the purpose of continuing the action of the| condenser when the main engines are not

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working. Such supplementary pump may beplaced in the chamber of the main pump, orit may be placed apart, and communicatetherewith by pipes or passages; in all cases,however, the valves of the main pump actalso for the supplementary pump. Or, in-stead of such arrangement, provision may bemade for disconnecting the main pump fromthe main shaft, and for driving it by auxiliarypower.”

The surface condensers in this case areplaced directly beyond on each side of thecylinder, fore and aft of the same, the pumpsbeing single-acting of the ordinary kind. Itwill be noticed that the inventors especiallyrecognize the effect of the pump’s connectionwith the cylinder by guiding the piston rod ofthe latter. Doubtless a better mode will be todispense with the idea altogether, and workthe pumps as in the example alluded to inpage 201, and represented by Fig. 45. Whilein some instances a horizontal arrangement ispreferred, and likewise a double-action.

Now with double-acting pumps the dia-meters are lessened, but the valves increasedin number, and thus the horizontal actionoften deemed preferable to a vertical. Acompact horizontal arrangement for thepumps can be attained by working themfrom the lower ends of the steam cylinders,centrally. With a stroke of four feet forthe steam piston, a motion of two feet forthe pumps can be effected, by putting thecentre of the swing bar four feet from thatof the trunnion ; the bar being secured to thecentre of the cylinder. A shorter strokecan be given to the pumps, while raisingthem also, by reducing the length of the bar.