( 434 ) 



On the Output of the N on- condensing Steam Engine, 

 as a Function of Speed and Pressure * 



By Francis E. Nipher. 



In the discussion which follows, the engine is supposed to be 

 running at a fixed cut-oft', and without change in the throttle. 

 The pressure changes required to produce a change of speed are 

 supposed to be effected by a change in boiler pressure. The 

 effect of the throttle or the governor with automatic cut-oft' will 

 be pointed out as we proceed. 



The difference between the two belt-pulls, or the load on the 

 brake, is represented by zc\ r being the brake-arm, or radius 

 of the driving-wheel. If the belt-pulls are jF' and i^", then 

 -^' — F"' = ~v. It is supposed also that the mean effective pres- 

 sure required to drive the engine when w ^ c? is constant for all 

 speeds. In an engine with balanced valves and where the amount 

 of lubrication used increases with the speed, this assumption 

 may be tolerated for a general treatment of the case, although 

 the peculiarities of engines will doubtless cause them to depart 

 from this assumption in a more or less irregular way. Engines 

 are usually built for definite speeds, and often behave poorly 

 when run at widely different speeds from those for which they 

 were designed. 



For these reasons, some portions of this treatment cannot lay 

 claim to very great precision. It will serve mainly to present 

 the general conditions of the problem, and may serve as a basis 

 for investigating the peculiarities of individual engines. 



Let Pq = mean effective pressure when w = c, 

 /'o == boiler pressure above atmospheric pressure when xv = o. 

 P = mean effective pressure with load w. 

 R =z piston radius, 

 / == stroke, fi = revolutions per minute. 



Then, during one stroke of the engine at uniform speed, 



* Re;id May 3oth, 1SS9. 



