Page:The Russell Engine-Four Valve Automatic Cut Off.djvu/11

 Fig. 21. The governor controls the speed of the engine through the cut—off eccentric, which fits loosely on the engine shaft and is connected with the weight arms in such a manner that the cut—off eccentric is moved around the engine shaft, either forward or backward, as the weights change their position, thereby cutting the steam off earlier or later in the stroke as the governor, or, more properly, the weights, adjust themselves to the load. When the cut—off eccentric is rotated forward, that is, around the shaft in the direction the engine runs, the steam is cut off earlier in the stroke; when the eccentric is rotated backward, the steam is cut off later in the stroke. The extreme range of cut—off is from "o" to ⅜; or ¾ of the stroke, or where it meets the fixed cut—off of the main valve, and this whole range of adjustment is under complete control of the governor. The value of this feature will be appreciated when it is understood that, with single eccentric releasing gear movement, the governor can only control the time of release during the opening movement of the valve, which necessarily terminates before mid-stroke, by an amount determined by the angular advance necessary for exhaust, so that if the release is not effected before mid—stroke, it will not take place at all during that stroke, thus causing extravagant expenditure of steam and spasmodic irregularities in the motion. To preserve a certain determined speed, with the smallest possible variation as changes occur in the load or pressure, is the function of the governor. The cut—off must always be proportioned to the load. When the engine is running empty, the steam is cut off at the beginning of the stroke, and the governor weights are at their extreme outer position. With a heavy load, Steam follows further and the weights are nearer their inner position. Between these two limits any number of positions of the weights and corresponding angular positions of the cut-off eccentric may be had, and as the steam is thus adapted to the load in each position, it follows