196 OF THE CONSTRUCTION OF [ SEC T. vi. 



the stroke by 103 for machinery, or by 98 1 for raising water (art. 337 and 342). 

 The area of the steam passages should be equal to the area of the cylinder 

 multiplied by the velocity of the piston in feet per minute, and divided by 4800 

 (art. 154). The air pump should be ith of the capacity of the cylinder, or i the 

 diameter, and i the length of the stroke of the cylinders (art. 351), and the con- 

 denser should be of the same capacity. The quantity of steam will be found by 

 multiplying the area of the cylinder in feet by the velocity in feet, with an 

 addition of T*ath for cooling and waste ; and this divided by the volume of the 

 steam corresponding to its force, in the boiler (art. 121.) gives the quantity of 

 water required for steam per minute, from whence the proportions of the boiler 

 may be determined (see Sect. in. art. 224 and 227) : at the common pressure of 

 2 Ibs. per circular inch on the valve, the divisor will be 1497. The quantity of 

 injection water should be 24 times that required for steam (art. 284), and the 

 diameter of the injection pipe ^Vth of the diameter of the cylinder. The valves in 

 the air pump bucket should be as large as they can be made, and the discharge 

 and foot valves not less than the same area. For the proportions of the beams 

 and other parts for strength, see Sect. vii. ; and for the modes of regulation 

 and management, see Sect. vin. 



416. To determine the power of a double acting engine. 



Let the force of the steam in the boiler be denoted by - - 1-000 



Then, besides the loss from uncondensed steam, there is loss, 



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



the cylinder, (art. 154.) -007 



2. By the cooling in the cylinder, (art. 157.) and pipes, 



(art. 148.) - -016 



3. By the friction of the piston and loss, (art. 474.) -125 



4. By the force necessary to expel the steam through the 



passages, (art. 154.) -007 



5. By the force required to open and close the valves, 



raise injection water, and the friction of the axes -063 



6. By the steam being cut off before the end of the stroke -100 



7. By the power required to work the air pump, (art. 



354.) -050 



368 



632 

 1 See note, page 167. 



