260 ENGINE TESTS. 



these functions are not so perfectly performed in the engines 

 which run at high speed, and there is a loss of economy. 

 Furthermore, the valves in the high-speed engines are generally 

 of some balanced type ; and valves of this kind are not so well 

 adapted to tight construction, and do not maintain so tight a 

 condition as those of the four valves in slow-speed engines. 

 Again, the high-speed engines usually require larger clearance 

 spaces in the cylinders than those of the slow-speed class. For 

 these various reasons, the high-speed engine is handicapped at 

 the outset with conditions which are unfavorable to economy ; 

 and if the effect of the high speed is advantageous, the 

 advantage must be so great as to overcome the losses noted if it 

 is to show in favor of the high-speed engine when it is sub- 

 jected to a test. An examination of the tests reported, taking 

 those engines which are run tit the highest speeds, shows that 

 in every case they are less economical than the slow-speed 

 engines, and in every case the reason appears in one or more of 

 the points mentioned. There is a further reason for the com- 

 paratively low economy of the high-speed engines reported, in 

 the fact that in almost all cases the engines given are of com- 

 paratively small size ; and this, no doubt, has an important 

 influence in making the engine less economical than it would 

 otherwise be. 



There is one case given where a Corliss engine was run at a 

 speed of one hundred and twenty revolutions per minute, that 

 of Engine No. 56 ; and this may be compared with the other 

 Corliss engines running a lower speed. The comparison, how- 

 ever, is not a very satisfactory one ; because the valves and 

 pistons were not in the best condition in regard to leakage, and 

 the boiler pressure was rather lower than that obtained on other 

 engines with which it could be compared. Looking at the 

 proportion of steam accounted for by the indicator, which is 

 .813, there is nothing in this indication to show any marked 

 improvement due to the high rotative speed, if such existed. 



