Les moteurs diesel pour la terre et les travaux maritimes . fference peut être jusqu'à 50  %. L'air de balayage n'entre pas dans l'cylindersdirect, mais passe par un récepteur, habituellement de petite dimen-sions, qui est souhaitable du point de vue de la pression d'être allowingthe rapidement soulevé et maintenu constant-aparticularly important pour les moteurs marins whenreversing. Dans la plupart des moteurs à deux temps qui havehitherto été construit pour travaux maritimes l'admission d'scavengeair s'effectue dans les soupapes actionnées par leviers dans turnoperated des cames sur l'arbre à cames, tout comme l'valvesin la f

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Diesel engines for land and marine work . fference may be as much as 50per cent. The scavenging air does not enter the cylindersdirect, but passes through a receiver, usually of small dimen-sions, which is desirable from the point of view of allowingthe pressure to be rapidly raised and kept constant—aparticularly important matter for marine engines whenreversing. In most of the two-cycle engines which havehitherto been built for marine work the admission of scavengeair is carried out through valves actuated by levers in turnoperated by cams on the cam shaft, just as the exhaust valvesin the four-cycle engine. The arrangement adopted bysome firms is shown in Fig. 86, two scavenge valves beingemployed for each cylinder, one on each side of the fuel inletvalve. In the first position in Fig. 86 the piston is at the 190 DIESEL ENGINES FOR LAND AND MARINE WORK top dead centre and the fuel valve is open to admit the oil, in the third position the exhaust ports are fully uncovered, the exhaust gas being expelled by the incoming air.. For larger engines, valves are inconvenient for the admis-sion of the scavenge air, owing to the size necessitated toaUow the requisite amount of air. For this reason ports DIESEL ENGINES FOR MARINE WORK 191 instead of valves have recently been introduced, andwith this arrangement there are two sets of ports at thebottom of the cylinder, one on each side for the exhaust andfor the scavenge air. Thismethod may be generallyemployed for all marineengines of the two-cycletype in the future, possess-ing as it does the advan-tage of simplicity, con-venience and rehability, though there seems to besome doubt as to whetherit gives so efficient ascavenging effect. Thereare then but two (andin some cases only one)valves for each cylinder—the fuel inlet valve andthe starting valve—andthis practically reducesthe operation of revers-ing to an alternation ofthe position of two cams, or possibly one. Fig. 87 shows diagram-matically the arrangementof ports

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