All About Engines

I24 All About Engines is attached by pin joints to a link hanging from a pin on the stand of the governor. The valve rod, which has a pin joint just outside the stuffing box, is sus- pended by a small rod from the collar on the gover- nor spindle, while the extreme end is forked, and attached by a pin to a block which is free to slide up and down in the slot in the link. Now, the movement of the eccentric rod is con- stant ; but the travel of the valve rod depends upon the position of the sliding block. If this is high, the travel of the valve rod is shortened ; if it is low, the travel is lengthened. A high position gives an early cut-off, a low position a late cut-off. And as the speed of the governor varies with the speed of the engine, the varying movement of the valve regu- lates very delicately the quantity of steam used. Whenever you see a non-reversing engine with two eccentrics to one cylinder you may be sure that a Meyer’s expansion valve is being used, and you will soon be able to ascertain whether this valve is or is not controlled by the governor. The latter may be of the Hartnell type, and if it is it may not be a very prominent object. It may be horizontal or vertical, and entirely enclosed, so that the rotating balls are not visible. But the slotted link will supply the clue. Incidentally, it may be remarked that the chief difficulty in securing very fine regulation of the speed is the tendency of the governor to “ hunt.” When the engine increases suddenly in speed an appreciable interval occurs before the governor responds; and when it does act it goes too far and