176 OF THE CONSTRUCTION OF [SECT. v. 



1. By the force producing motion of the steam into the 



cylinder, (art. 154.) - '0069 



2. By the cooling in the cylinder and pipes, (art. 158.) '016 



3. By the friction of the piston and waste - '2000 



4. By the force required to expel the steam into the 



atmosphere, (art. 154.) - - -0069 



5. By the force expended in opening valves, and friction 



of the parts of the engine '0622 



6. By the steam being cut off before the termination of 



the stroke, (art. 363.) -1000 



3920 



We may consider this 0'4, and then the effective pressure is 0'6 of the force of the 

 steam in the boiler, diminished by the pressure of the atmosphere ; whence we have 

 the following rule for the power of an engine of this species. 



368. RULE. For noncondensing engines working at full pressure. Multiply 

 six-tenths of the excess of the force of the steam in the boiler, less four-tenths of 

 the pressure of the atmosphere in Ibs. on a circular inch, by the square of the 

 diameter of the cylinder in inches, and by the velocity of the piston in feet per 

 minute ; the product is the power of the engine in Ibs. raised 1 foot high per 

 minute. 1 



To find its equivalent in horse power, divide by 33000. 



Example. Let the diameter of the cylinder be 11 inches, the length of the 

 stroke 2 '5 feet, the number of strokes per minute 33, and the force of the steam in 

 the boiler 24 Ibs. per circular inch above the atmospheric pressure : in this case 

 the velocity is 2 x 2'5 x 33 = 165 feet, and (24 x 0-6 - 11-5 x 0-4) x 121 x 165 

 = 195657 Ibs. raised 1 foot per minute. 



And, 



= 6 horse power nearly. 



369. If the area of the cylinder in feet be multiplied by the velocity of the 

 engine in feet per minute, it will be the volume of steam consumed when of the 

 density of that in the boiler ; and, dividing by the volume of steam which a cubic 



1 Put a = the diameter of the cylinder in inches, t; = the velocity of the piston in feet per 

 minute, and/= the force of the steam in the boiler in inches of mercury; then, 



^ ~ . x a 2 v = the power in Ibs. raised 1 foot per minute, 

 * o 



2-6 inches of mercury being 1 Ib. per circular inch. 



