242 . Kansas Academy of Science. 



duced on a reduced scale coincident with and by the movement of 

 the engine cross-head, and thereby tracing a horizontal line on the 

 paper drum at any time a contact is made between the drum and 

 pencil. The other is the vertical movement of the pencil parallel 

 to the axis of the drum, and is produced by the steam pressure act- 

 ing on the piston of the indicator and forcing it to a height propor- 

 tionate to the pressure upon the piston. Consequently, the length 

 of the diagram represents the stroke of the engine on a reduced 

 scale, while tlie vertical height at any point represents the pressure 

 upon the indicator piston at a corresponding point in the stroke of 

 the engine. 



We will first study some distortions of the card from the ideal 

 form due to faults of the indicator or its connections. 



Should the reducing mechanism used not produce the exact 

 piston motion reduced, or have lost motion in any of its parts, the 

 card will not give a true record of what takes place. This might 

 easily mislead one regarding what actually took place ; so that it is 

 essential our reducing mechanism be an accurate one and in good 

 order. 



If the steam passages from the cylinder to the indicator are not 

 ample the card will be reduced in height, the initial pressures 

 falling further than we would expect below the boiler pressure. A 

 diagram taken from the steam-chest will usually locate this trouble. 



Waves in a line of the card are caused by the inertia of the in- 

 dicator parts when the pressure on its piston is suddenly changed. 

 These waves become more marked as the speed of the engine in- 

 creases, and at high speed cause the card to be much distorted. 

 The distortion from this cause is also increased when the indicator 

 spring used is too weak for the pressure. A spring should be used 

 which will reduce this efPect as much as possible without causing 

 the card to be too low to indicate accurately engine faults. 



The lines indicating rising or falling pressure will sometimes 

 have steps in them. This is caused by the indicator mechanism 

 sticking, usually by the piston becoming gummed up and sticking 

 in its drum or cylinder. 



A wave in a line of the card sometimes appears where we would 

 not expect it from the indicator's inertia or other expected deform- 

 ing forces, and this can usually be traced to the cord leading from 

 the reducing mechanism rubbing or striking against some object. 



The card from extremity to extremity should be as long as the 

 atmospheric line, any difference in this respect showing unequal 

 tension of the cord. Unequal pressure of the pencil against the 



