OF THE HYDROSTATIC PRESS. 123 



RULE. Multiply the entire pressure on the piston of the 

 cylinder, by the square of the diameter of the indicator or 

 safety valve, and divide the product by the square of the 

 diameter of the cylinder for the weight required. 



130. EXAMPLE 6. The diameter of the safety valve is J of an inch, 

 that of the cylinder 5 inches, and the weight on the safety valve 

 46.875 Ibs. ; what is the corresponding pressure on the piston of the 

 cylinder ? 



Here we have given 3 = of an inch ; D zz: 5 inches, and 

 w zz:46.875 Ibs ; therefore, by substitution, equation (93) becomes 



.25 2 P = 5 2 x 46.875, 

 and by division, we obtain 



The general expression for the value of P, as derived from the 

 equation marked (93), becomes 



* 

 - 



(96). 



And the practical rule supplied by this equation, may be expressed 

 in words as follows. 



RULE. Multiply the weight on the safety valve, by the 

 square of the diameter of the cylinder, and divide the product 

 by the square of the diameter of the safety valve, and the 

 quotient will give the entire pressure on the piston of the 

 cylinder. 



131. EXAMPLE 7. The diameter of the cylinder is 5 inches, the 

 entire pressure of the piston is 18750 Ibs., and the weight on the 

 safety valve is 46.875 Ibs. ; what is its diameter ? 



Here we have given ozz:5 inches ; P zz: 18750 Ibs., and wzr46.875 

 Ibs. ; therefore, by substitution, equation (93) becomes 



18750a 2 z=5 2 X 46.875, 

 and from this, by division, we get 



and by extracting the square root, we obtain 



3= -V/ .0625 zz: .25, or of an inch. 



The general expression for the value of 3, as derived from the 

 equation (93), is as follows, viz. 



