'Mathematical and Physical Papers. 239 



THE INTERPRETATION OF INDICATOR DIAGRAMS. 



By Charles I. Corp, Lawrence. 



^^HE important and essential knowledge to be derived from a 

 -*- careful investigation and study of indicator diagrams is in- 

 valuable to the engineer, as they enable him easily to ascertain 

 and establish various facts concerning the use of steam that by 

 any other method would prove complicated and unsatisfactory, of 

 which the following may be stated : 



First. It shows whether the valves of an engine are correctly 

 and evenly timed, and also serves as a guide in all necessary ad- 

 justments of the same that may be required, in order to insure the 

 best distribution of the steam working within the cylinder, and 

 thereby securing the maximum economy and efficiency of the en- 

 gine. 



Second. The indicator power developed in the cylinder of an 

 engine may be determined ; also the quantity of energy lost in va- 

 rious ways ; such as leakage of valves, back pressure, too early re- 

 lease, and incorrect adjustment of valves. 



Third. It indicates whether the steam-ports and passages are 

 adequate in size, and a diagram taken from the steam-chest will 

 also show whether the steam-pipe and its connections are of 

 sufficient size. 



Fourth. It indicates the condition of the valves and piston in 

 reference to the leakage. 



Fifth. In connection with a feed-water test (showing the ac- 

 tual amount of steam consumed), the economy with which the 

 engine works may be determined. 



To ascertain with accuracy each and every item of infor- 

 mation mentioned above, it, is absolutely essential that the diagram 

 should truly represent the position of the piston, and also the pres- 

 sure exerted on both sides of it, at every point of its stroke. 



The general features of a diagram that indicate a proper distri- 

 bution of the steam in an engine cylinder is represented by dia- 

 gram, the attainment of which (as near as possible) should be the 

 endeavor of an engineer in setting the valves of his engine. AA 

 is the atmospheric line and £B represents the boiler pressure. 



