Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

______________________ 490 _______________________________________ moleswobth’s pocket-book Proportions of Safety-valve, Levers, &c. D = Diameter of valve in inches. A = Area of valve in inches. W = Weight in lbs. P = Pressure in lbs. per square inch on the safety-valves. The proportion of I = D and L = D A gives 1 lb. per square inch for each lb. at the end of the lever. In addition to the weight W, the weight of the lever and the valve itself must be allowed for. Let G = Distance of centre of gravity of lever from fulcrum. w = Weight of lever. X = Weight of the valve. Gw__c Pressure per square inch due to the weight of TÄ - t lever. X __ i Pressure per square inch, due to the weight of ~ ~ i the valve. The mitre of safety-valves should not exceed inch in width. Akea of Safety-valves. A = Area of fire-grate. a = Area of safety-valve. a —’006 A. For land engines the proportion of • 8 inch per nominal horse-power is sometimes adopted.