GOVERNORS. We present a variety of the latest improved types of governors.
Boll's Shaft-Governor.—Mv. Prank If. Ball has recently made a new application of a dash-pot to centrifugal governors. which seems to he free from the difficulty formerly en countered with dash-pots in this connection. It is thus described in Trans. A. S. -11. vol. ix : "The principles involved may be understood by reference to Fig. I. The governor here shown is one of the ordinary forms of shifting eccentric governors. The introduction of the spring S between the dasl pot and the movable part of the governor is the new feat ure. Its operation and effect are as follows: Suppose the long spring D be drawn up until its initial tension, in dis Lance of stretch, shall corre spond exactly with the dis tance between the center of gravity of the weight and the axis of revolution. This is what is called' full theoretic tension.' The condition is the same as would be obtained if the weights were first placed at the center of the shaft, and after attaching the spring without any tension the weight was then moved out to the position shown. With this relation between the position of the weight and the tension of the spring,The increase and decrease of centrifugal force caused by moving the weight to or from the axis of revolution would exactly harmonize with the changes of resistance of the spring due to said motion : and if the two forces were in equilibrium in one position, they would be so in every position at the same speed. This condition, as has already been said, should be expected to give uniform speed of the engine at every position of the governor, but has been found impracticable on account of its instability. The object of the dash-pot and spring here shown is to allow the theoretically perfect adjustment of the long spring, and to furnish ample stability without making the governor sluggish, or in the least preventing a quick and delicate balancing of the forces. This spring S is arranged for both compression and extension, and has a range of deflection sufficient to allow the full motion of the governor, from one extreme to the other, without regard to the motion of the piston of the dash-pot to which it is attached. The re
sistance of this spring S. having no initial tension, is entirely out of harmony with the other spring. and combined with them produces exactly the effect when motion takes place that is obtained ordinarily in centrifugal governors, by using springs with less than the full theoretic tension and if the dash-pot piston should remain stationary, the same change of speed would be found between the extreme positions of the governor : but by reason of the move ment of this piston, the tension on spring S is released, and it then ceases to be a factor in the speed, which is only the result of the long spring, and, as has been previously shown, it most be the same at every position of the weight. This theory, though somewhat obscure, seems to be correct, and its practical operation under careful tests proves it to be so." Governors are now made of various types. embodying this principle, and have been found to compel the some number of revolutions per min, of the engine under any condition of load or boiler-pressure within the full capacity of the engine.
Smith's Governor is shown in Figs. 2 and 3. It is described at length in Trans. A. S. _M. E., vol. xi. It was designed on the basis of the following propositions: First, a governor to be sensitive must be as free as possible of friction. Second. to be powerful. the forces which are in equilibrium must be large compared with the resistance of the valve to be moved.
Third, in order that the shaft may not be thrown out of balance by change of position of the governor-weights, these weights must Ire symmetrical. Fourth, that the engine may make long runs the joints of the governor must be so constructed as not to require oil, or be eapable of lu brication while in !notion.