STEAM BOILERS 115 



SOLUTION. Applying the formula 



83.1 



Roper's Safety-Valve Rules. Some inspectors of the United 

 States Steamboat Inspection Service prefer to have lever 

 safety-valve problems worked out by the rules that follow, 

 known among American marine engineers as Roper's rules. 

 A candidate for a marine engineer's license should always use 

 Roper's rules when he knows that they are preferred by the 

 examining inspector. 



Let A = area of valve, in square inches; 



D = distance from center line of valve to fulcrum, in 



inches; 



L = distance of weight from fulcrum, in inches; 

 P = steam pressure in pounds, per square inch; 

 W= weight of load or weight on lever, in pounds; 

 V = weight of valve and stem, in pounds; 

 w = weight of lever, in pounds ; 

 1 = distance from fulcrum to center of gravity of lever, 



in inches. 



Then, the pressure at which the safety-valve will blow off is 

 found by the formula 



r _WL+wl+VD 



A D 



If the distance L is known, the weight W to be hung on 

 the lever is found by the formula 



L 



The distance L from the fulcrum to the point at which the 

 weight W is hung is found by the formula 

 APD-(wl+VD) 

 W 



Area of Safety Valve. By area of safety valve is meant the 

 area of the opening in the valve seat; that is, the area of the 

 surface of the valve in contact with steam when the valve 

 is closed. The size of the valve relative to the size of the 

 boiler and the working pressure is prescribed by law in 

 many localities, and must be made to conform to the law 



