A safety-valve, in which a weight is employed. Here a is the valve, b b the boiler, c c the valve-seat, usually, like the valve itself, made of gunmetal, d the lever turning upon a fixed center at e, and pressing upon the valve by a steel point f, a guide for the lever g a weight which may be shifted backwards and forwards according to the pressure desired.
Logan Marshall, Ed. International Self-Pronouncing Reference Library (five vols.) (Philadelphia, PA: International Press, 1911)