SECT. VII .] STEAM ENGINES. 241 



For head links it becomes, 



_ ,/~p~= b t = the breadth multiplied by the thickness in inches. 



o4 



504. RULE. Multiply the diameter of the steam piston in inches, by the 

 square root of twice the elastic force of the steam in the boiler, in Ibs. per circular 

 inch, and the product divided by 84 is the diameter of the rod in inches. 



Example. If the force of the steam be 16 Ibs. per circular inch, and the diameter 

 of the cylinder 54 inches, then the square root of 32 is 5'657, and 



54 X ftT - = 3 ' 6 mcnes > the diameter required. 



OTT 



For the atmospheric pressure it is one-sixteenth of the diameter. 



505. OF THE STRENGTH OF RODS ALTERNATELY EXTENDED AND COMPRESSED. In 



the compression of rods the force increases with the flexure ; but if the length never 

 exceed about thirty-six times the diameter, its error will be very small to assume that 

 degree of flexure ; and by taking in addition the greatest possible deviation, from 

 misfitting, which is half the diameter of the rod, 1 with this simplification we have 



D-P =nearl, or. = 



For cast iron/ = 15300, and a = -^ </~T>. 



For malleable iron /= 17800, and a = ^ 



For tempered steel f= 45000, and a = -70" 



This rule applies to piston rods of double engines, parallel motion rods, air pump 

 and force pump rods, and the like ; and if P be increased in the ratio of the radius 

 to the sine of the greatest angle a connecting rod makes with the direction, it 

 applies to connecting rods. 



506. RULE. Multiply the diameter of the piston in inches by the square root 

 of twice the pressure of the steam in Ibs. on a circular inch, and divide the 

 product by, 



42 for cast iron, 

 45 wrought iron, 

 72 tempered steel ; 

 the quotient will be the diameter in inches. 



Example 1. The force of the steam being 16 Ibs. per circular inch, and the 

 diameter of the piston 80 inches, that of the piston rod should be, for wrought iron, 



80 x */~m 

 jg - = 10-06 inches. 



Example 2. The force of the steam being 4 atmospheres = 46 Ibs. per circular 



1 Practical Essay on Cast Iron, art. 246. 

 2 H 



