ENGINE No. 9O. 



Diagrams 90 a and 90 b are introduced partly as curiosities 

 and partly to show the general features of diagrams obtained 

 from a steam-driven air-pump operating an independent con- 

 denser. Here the cylinder was 10" x 10". Diagram 90 a was 

 taken when the pump exhausted into the condenser, and dia- 

 gram 90 & when it exhausted into the atmosphere. The pecu- 

 liarity of these diagrams lies in the fact that the pump takes 

 steam at full stroke, exhausts at a higher pressure than the 

 pressure of admission ; and the return stroke is made, for a por- 

 tion at least, under the wasteful conditions of a very high back 

 pressure. Another curiosity is the stopping of the piston at 

 about the middle of the stroke, and the rebounding of the same 

 before it proceeds on its course. 



When this pump was running non-condensing the exhaust 

 steam was measured by collecting and condensing it in a barrel 

 of water. It was found to use 717 Ibs. of steam per hour, at a 

 speed of 61.2 double strokes per minute, or 103.3 Ibs. of steam 

 per I. H. P. per hour, the power developed being 6.94 H. P. 

 This performance represents, as might be expected, a very 

 wasteful use of steam ; but it should be stated that in a plant 

 properly arranged the heat of the steam can be utilized in 

 warming the feed-water, and the loss is reduced to a compara- 

 tively small quantity. 



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