RULES FOR CALCULATING THE STEAM ENGINE. 209 



1 j times the cubic feet of boiler per horse power, for ( wrou S ht iron 

 i J I copper ; 



150" 



the result will be the thickness of the upper plates in inches. 



The bottom plates should be as much thicker as will compensate for wear ; usually twice 

 the thickness of the top ones. (252.) 



Example. In a rectangular boiler, the greatest diagonal being 8 feet 2 inches = 98 inches, 

 the load on the valve 6 Ins. per square inch, and the space for steam for each horse power 

 18 cubic feet ; required the thickness of the top plates, to be made of wrought iron. 



18 cubic feet 98 inches 



150 6 ffis. 



900 27|00) 5|88 (0'218 of an inch for the top plates. 



18 54 



2700 48 



27 



210 

 The bottom plates should be the double of 0'218 or 0'436 of an inch. 



5. To find the requisite thickness of a spherical boiler. 



RULE. Multiply the diameter in inches by the pressure on the valve in ffis. per square 

 inch, and divide by 



n f times the cubic feet of boiler per horse power, for \ v 

 1 ou J I. copper y 



the result will be the thickness in inches. (252.) 



Example, A spherical wrought iron boiler, 18 feet 8 inches = 224 inches diameter, with 

 20 cubic feet to each horse power, and the load on the valve being 8 Ibs. per square 

 inch ; required its thickness. 



20 cubic feet 224 inches 



300 8 IDS. 



6000 6|000) 1|792 



0'3 of an inch thickness. 



6. To find the height of a column of water to supply a boiler against any proposed pressure 

 of steam. 



RULE. Multiply the pressure in ffis. per square inch by 2'44, and the product will express 

 the required height in feet. (141.) 



Example. Required the length of feed pipe capable of supplying a boiler when the pressure 



is 5 ffis. per square inch. 



2-44 



5 



12-20 



12'2 or 12 feet 3 inches above the surface of the 

 water in the boiler. 



