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An illustration of a lever safety valve. "Suppose the valve A is just suppose to open when the steam pressure under it is 120 lb. per square inch, that mean area of the valve exposed to steam pressure is 4 square inches, the weight of the valve 4ln., the distance C D being 3 inches the centre of gravity of the lever 7 inches from D, and its weight 6 lb.; where must the weight E - which is 50 lb. - be placed on the lever? The total upward force on the valve is 120 × 4 - 4 = 476 lb., and the moment of this force about D is 476 × 3 = 1428. This is the only negative moment, all other forces tending to turn the lever the opposite way." -New, 1891

Lever Safety Valve

An illustration of a lever safety valve. "Suppose the valve A is just suppose to open when the steam…