The center of gravity is the point at which the lever and valve attached to it will just balance over a balancing bar (bar with knife edge). The fulcrum is at the center of the pivot on which the lever works.
Where F = the fulcrum on which the lever works. W = weight of ball in pounds. g = distance in inches from fulcrum to center of gravity. Vl = weight of valve and lever in pounds. L = distance between ball and center of fulcrum in inches. / = distance between fulcrum and center of valve in inches. P = boiler pressure per square inch. A - area of safety valve in square inches.
Then W = A X P X l - (Vl x g) / L and L = A X P X l - (Vl x g) / W
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Fig. 165. - Safety Valve.
Example. - At what distance from the center of fulcrum must a weight be placed, if the boiler pressure is 100 lbs., weight is 16 lbs., area of valve is 3 sq. in., and valve and lever weigh 16 lbs., center of valve is 2 1/2 in. from fulcrum, and center of gravity is 12 in. from fulcrum?