190 



STEAM ENGIXES 



Approximate M. E. P. If an indicator is not available, so 

 that diagrams may be taken in order to determine the M. E. P. 

 of an engine, the value of the M. E. P. may be estimated by 

 the formula 



in which P = M. E. P., in pounds per square inch; 



C = constant corresponding to cut-off, taken from 



accompanying table; 

 p = boiler pressure, in pounds per square inch, gauge. 



The foregoing formula applies only to a simple non- 

 condensing engine. If the engine is a simple condensing 

 engine, the formula should be altered by substituting for 17 

 the pressure existing in the condenser, in pounds per square 

 inch. 



CONSTANTS USED IN CALCULATING M. E. P. 



In this table, the fraction indicating the point of cut-off is 

 obtained by dividing the distance that the piston has traveled 

 when the steam is cut off by the whole length of the stroke; 

 that is, it is the apparent cut-off. It is to be observed that 

 this rule cannot be applied to a compound engine or to any 

 other engine in which the steam is expanded in successive 

 stages in several cylinders. 



EXAMPLE. Find the approximate M. E. P. of a non-con- 

 densing engine cutting off at $ stroke, if the boiler pressure is 

 80 lb., gauge. 



SOLUTION. According to the table, the constant correspond- 

 ing to cut-off at J stroke is C = .864. Then, applying the for- 

 mula, P = .9[.864(80+ 14.7) -17] = 58.34 lb. per sq. in. 



