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308 according as the engine is running in the ahead or astern direction. In some designs, reversing is accom- plished by employing only one cam for the scavenge air valve, and one - for the fuel inlet valve, and arrang- ing the setting of these cams so that by turning the camshaft through a certain angle, relative to the crank- shaft, the cams are brought into the required position, but in that case. special arrangements must be made for the starting air-inlet valves. If two cams are provided for each valve, and the camshaft is moved longitudi- nally for reversing, some difficulty arises with the scavenge valve, owing to the presence of compressed air in one or two of the cylinders when the engine stops, and it is evident that a single cam is sufficient for actuating the scavenge air-inlet valve, provided the shaft on which it is mounted is turned through the requisite angle. Features of Carels Design In the design adopted by Messrs. Carels, the camshaft is capable of turning through an angle relative to the crankshaft, so that the scavenge valves are set in the position for astern running, and by this means only one scavenge valve is required per cylinder. For the starting and fuel inlet valves, two separate cams, side by side, are provided for each cylinder, and to bring the astern set into action another shaft, directly in front of the camshaft, is moved in a longitudinal direction. This causes the rollers of the fuel and starting valve levers to take up _ positions above the astern set of cams, on the camshaft, the operation being effected by means of the intermediary levers. The camshaft is driven in a manner 'similar to that adopted in land en- gines from the crankshaft, by means Of spiral gearing, and the. vertical shaft A. An ingenious and _ simple iInethod is adopted of rotating. the camshaft relative to the crankshaft, this being accomplished merely by raising the vertical spindle A, which is provided with a sort of sleeve coup- ling. This movement is effected by a small air motor, which is controlled by the lever B, whilst in the case of fail- _ure of the air motor the operation can be carried out by hand by 'the wheel C. The hand wheel D. is interlocked with the gear for rotating the cam- shaft, and can only be moved when this is properly set, and it serves as the maneuvering wheel for starting up the engine and reversing. On turning this hand wheel when requir- ing to run astern, after 'shutting off fuel admission, compressed air is first introduced, the motor thus rapidly THE MARINE REVIEW September, 1912 ANIONY ANIMVI TSaIq-staavD "d "H "A OOOT "SHaNITAD-¥nNOY Y aulsDU jasaiq -sjai0)'d'y'9 OOOT Jopuydo-inof