SECT. .] ' PROPERTIES OF STEAM. 95 



Multiply the length of the stroke by the number of strokes per minute, and 

 divide the product by 2400 ; the square root of the quotient multiplied by the 

 diameter of the cylinder is the diameter of the pipe. 



Example. To find the diameter for the steam pipe of an engine of which the 

 diameter of the cylinder is 2 feet, the length of the stroke 2'5 feet, and the 

 number of strokes per minute 38 ; 



38 x 2-5 _ _95_ J_ 

 2400 = 2400 ~~ 25' 



and the square root of TS is one-fifth ; hence the diameter of the steam pipe in this 

 case is one-fifth of that of the cylinder. 



The same rule applies to both high pressure and low pressure steam engines, 

 and both to the steam passages and the passages to the condenser ; and the excess 

 of force necessary to produce the velocity is very nearly one- 144th part of the 

 force of the steam. 



OF THE Loss OF FORCE BY THE COOLING OF THE CYLINDER. 



155. The steam after it gets within the cylinder is liable to a loss of force 

 by cooling. It is, in large engines, usually inclosed by a case called a jacket, and 

 steam is introduced between this case and the cylinder to keep the latter hot ; but 

 the loss in fuel by this mode is the same as with a naked cylinder, and there is 

 clearly no advantage in preserving the force of the steam by adding this case, 

 unless it be supplied with steam by a separate pipe. (See art. 147.) 



156. The investigation for the loss of force in the steam pipe applies in the 

 case of a naked cylinder with a very slight alteration. The steam in this case is 

 progressively exposed to the sides of the cylinder ; hence the loss will be some 



and when we use the length of the stroke I, and the number per minute m ; 2 / m = 60 V, and we 

 may take 



Aim 



a =- 



90 V 459 + t 



When t' = 220, it becomes 



Aim 

 2400 



which is the same as the rule. If t' = 320, then 



_ Aim 

 ~ 2520 



showing that a rather smaller aperture will do for high pressure steam. A is the area of the 

 cylinder, and a the area of the pipe, in superficial inches. 



