The Governor

The governor, or “fly-ball governor,” as it is often distinctively called, was another of Watt’s minor but very essential inventions. Two heavy iron or brass balls (B and B) were suspended from pins (C and Ct') in a little cross-piece carried on the head of a vertical spindle (A and A') driven by the engine. The speed of the engine varying, that of the spindle changed correspondingly, and the faster the balls were swung the farther they separated. When the engine’s speed decreased, the period of revolution of the balls was increased, and they fell back toward the spindle. Whenever the velocity of the engine was uniform, the balls preserved their distance from the spindle and remained at the same height, their altitude being determined by the relation existing between the force of gravity and centrifugal force in the temporary position of equilibrium. The distance from the point of suspension down to the level of the balls is always equal to 9.78 inches divided by the square of the number of revolutions per second, i.e. h = 9.78N.

The arms carrying the balls, or the balls themselves, are pinned to rods (M and M') which are connected to a piece (N and N'), sliding loosely on the spindle. A score cut in this piece engages a lever (V) and, as the balls rise and fall, a rod is moved, closing and opening the throttle-valve and thus adjusting the supply of steam in such a way as to preserve a nearly fixed speed of engine. The connection with the throttle-valve and with the cut-off valve-gear is seen not only in the engraving of the double-acting Watt engine, but also in those of the Greene and the Corliss engines. This contrivance had previously been used in regulating waterwheels and windmills. Watt’s invention consisted in its application to the regulation of the steam-engine...

Source: A History of the Growth of the Steam-Engine, by Robert H. Thurston, A. M., C. E., Professor of Mechanical Engineering in the Stevens Institute of Technology, Hoboken, N. J.; Member of the Institution of Engineers and Shipbuilders of Scotland, Associate British Institution of Naval Architects, etc., etc.; Published; New York: D. Appleton and Company, 549 and 551 Broadway. 1878.

Postcard advertisement sent to the Philadelphia Forging Works from the Shive Governor Company of Bethlehem, Pennsylvania.

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