DISCUSSION ON MAY MEETING PAPERS. 37 



that is obtained by the use of this system, but as a matter of fact there are many, and it was 

 because of these advantages that Messrs. Vickers some years ago decided to abandon the use 

 of the air blast system. Since that time every single engine that they had previously built 

 fitted with this air blast system has been altered to the mechanical injection system. 



I may briefly mention the advantages of the mechanical injection which the authors 

 have dismissed so lightly: 



1. Saznng in weight. — In a high-duty light-weight engine of 600 brake horse-power a 

 total net saving in weight of 4,887 pounds is effected by the substitution of the small fittings 

 required for the mechanical spraying system, for the air compressor and its attendant com- 

 plication of fittings and pipes. 



2. Sating in space. — In the case of the above engine, the overall length of the engine 

 is reduced by 3 feet, while further space is saved by the omission of the high-pressure and 

 low-pressure cooler pipes and their connections. 



3. Reduced cost. — The air compressor is an expensive auxiliary to the engine, and in 

 view of the simplicity of the mechanical injection system, it follows that the relative cost 

 of manufacture of the engine is less than that of the other type. 



4. Economy of fuel. — Consumptions down to 0.38 pound per brake horse-power per 

 hour, or 170 grammes per force de cheval, have been obtained on ordinary official trials. This 

 figure has not been attained in any other type of engine of which we have knowledge. 



5. Number of fittings and pipes reduced. — Less attention and adjustment of the engine 

 are required as compared with the air spraying system, due to the elimination of the valves 

 and pipes in connection with the air compressor, relieving the engineers in charge of the 

 engine and reducing the cost of upkeep and repairs. 



6. Economy of air for starting the engine. — Experience has demonstrated that the 

 engine will get under way more rapidly with mechanical spraying than with air spraying, 

 this effecting a considerable saving of starting air. Greater certainty is also obtained when 

 maneuvering the engine. 



7. Blast action on pistons. — There is a complete absence of blast or blow-pipe action on 

 the piston top, and of local heating of the piston, both of which faults have a tendency to 

 crack the pistons. 



Not the least of these advantages is the perfect safety of this system over and above the 

 chances of an accident with the air-blast injection system. 



I have in my hand a report of an accident to an air-blast injection engine which 

 occurred at the beginning of this year. The accident occurred to a large six-cylinder engine 

 in an ex-German vessel. I will not weary the meeting by reading the whole of this report, 

 but I will mention that the engine was started on fuel and made about SO revolutions ahead. 

 It was then reversed and it made a few revolutions astern when an explosion took place in 

 No. 1 spray valve. The damage done was as follows : 



No. I cylinder. — The top cast-iron casting of the spray valve body was burst into about 

 thirty pieces and scattered over the engine room. The nozzle end of the spray valve was 

 blown off into the cylinder. The forked lever for lifting the needle valve was broken off 

 and two Ij^-inch nuts were split and the studs broken off next to the spray valve. 



Nos. 2 and 5 cylinders. — ^The nozzle ends of the spray valves were blown off into the 

 cylinders. 



No. 6 cylinder. — The nozzle end of the spray valve was blown off into the cylinder. The 

 forked lever for lifting the needle valve was broken at the collar. The explosion was of a 



