The simplest type of governor, and the one commonly used on traction engines, is that which is only a modification of the one invented by Watt. Two balls revolve around a spindle in such a way as to rise when the speed of the engine is high, and fall when it is low, and in rising and falling they open and close a valve similar to the throttle valve. The amount that the governor valve is opened or closed by the rise and fall of the governor balls is usually regulated by a thumb screw at the top or side, or by what is called a handle nut, which is usually held firm by a check nut directly over it, which should be screwed firm against the handle nut. Motion is conveyed to the governor balls by a belt and a band wheel working on a mechanism of metred cogs.
There is considerable friction about a governor of this type and much energy is wasted in keeping it going. The valve stem or spindle passes through a steam-tight stuffing box, where it is liable to stick if the packing is too tight; and if this stuffing box leaks steam, there will be immediate loss of power.
PICKERING HORIZONTAL GOVERNOR.
Such a governor as has just been described is called a throttle valve governor. On high grade engines the difficulties inherent in this type of governor are overcome by making the governor control, not a valve in the steam supply pipe, but the admission of steam to the steam cylinder through the steam valve and its gear. Such engines are described as having an “automatic cut-off.” Sometimes the governor is attached to the link, sometimes to a separate valve, as in the Meyer gear already described. Usually the governor is attached to the fly-wheel, and consequently governors of this type are called fly-wheel governors. An automatic cut-off governor is from 15 per cent to 20 per cent more effective than a throttle valve governor.
CRANK, SHAFT AND JOURNALS.
We have already seen how the piston conveys its power through the piston rod, the cross-head, and the connecting rod, to the crank pin and crank, and hence to the shaft.
The key, gib, and strap are the effective means by which the connecting rod is attached, first to the wrist pin in the cross-head, and secondly to the crank pin on the crank.
The strap is usually made of two or three pieces of wrought iron or steel bolted together so as to hold the brasses, which are in two parts and loosely surround the pin. The brasses do not quite meet, and as they wear may be tightened up. This is effected by the gib, back of which is the key, which is commonly a wedge which may be driven in, or a screw, which presses on the back of the gib, which in turn forces together the brasses; and thus the length of the piston gear is kept uniform in spite of the wear, becoming neither shorter nor longer. When the brasses are so worn that they have been forced together, they must be taken out and filed equally on all four of the meeting ends, and shims, or thin pieces of sheet iron or the like placed back of them to equalize the wear, and prevent the piston gear from being shortened or otherwise altered.
