288 F. F. Nipher — Non-condensing Steam Engine. 



It may be remarked in passing that, for a constant value of P', 

 this is an hyperbola which represents the relation between 

 mean effective pressure and speed, with varying load. The 

 asymptotes of the curve are the vacuum line and the axis of 

 the parabola of maximum output, where 



. _ . . h+^P. + S 

 b + c 

 The only part of this curve which has any practical significance 

 is that included between the pressure axis and the line where 

 P=P . This part of the curve is marked P on fig. 2, P' 

 being the line representing the corresponding fixed boiler pres- 

 sure. During the operation here considered, the point repre- 

 senting the performance of the engine would travel through a 

 definite path on the surface represented by (4). The hyperbola 

 marked P on fig. 2 would be a projection of that path on the 

 plane P, n, while the parabola (10) with P' constant would be 

 a projection of that path on the plane HP, n. 



The engine might indeed be driven by a belt at a greater 

 speed than that given it by the steam when w = o, and the 

 mean effective pressure would continually fall as represented 

 by the hyperbola. The part of the curve corresponding to 

 negative values of n has no physical significance. The engine 

 when brought to rest with any fixed load w, by a decrease of 

 boiler pressure, would not reverse if the boiler pressure were 

 still more reduced, until it became less than the atmospheric 

 pressure. 



™ , • , • ,h„M InRHn 



Multiplying (21) by 



v J ft v i J 33000 



in* = 27tm ( km ( A + p o)^ +p > \ (22) 



33000\ h+ I\ + ti(b + c)n) ' v ; 



This equation corresponds to (10). 



The condition of maximum 7hp for constant P' is 



(h+P + JE)(h + Po)(h + P') 



= (h + P + F+ (b+c)n\ (23) 



h 



This like (11) is the equation of a parabola. The value of n is 



}l = - h±P»±z± _L \ (h+p 0+J t;)(h + p )(h+P) (24) 



The slope of this parabola is 



dP' h „ . h (b + cY . . , 



which when n = o is 



fdP'\ ._ . h 



