F. E. JVipher — JS 'on-condensing Steam Engine. 285 

 2nRHr (h + P ) {h + P')u n 



For any constant boiler pressure there will be some definite 

 speed which, will make Buy a maximum. The condition is 



'dBuB\ 



dn 



P' 



Imposing this condition we have 



(h + P'){h+Po + E)= [h + Po + E+(b+c)?iY . (11) 



The speed must be such that the boiler pressure required to 

 drive the unloaded engine at that speed, is a mean proportional 

 between the constant boiler pressure under consideration, and 

 the boiler pressure required to start the unloaded engine, [see 

 (7),] all pressures being measured from vacuum. The load 

 corresponding to this maximum is of course found by impos- 

 ing this condition in (9) by the elimination of n, 



P' 



J^^ 





Fig. 2. 





P' s^ constant. 







^^ P 



ID_^. 



~-^^~~ 





" ~ 







E 





Po 





Po 







Atmospheric Line 





h 



Vacuum Line 





Equation (11) gives the relation between n and P' for a 

 maximum output at any boiler pressure P'. It is the equation 

 of a parabola, which crosses the pressure axis at its intersection 

 with the line of zero load (7). The slope of this parabola is 



< 5 +<>' - . . (12) 



dn 



2(b+c) +2 



h+P a + E 



When n — o the slope is therefore twice that of the line of 

 zero load. 



The value of n in (11) is 



h + P !> + E , 1 | (h + JP +E) {b + P') 



b + c 



(13) 



