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main axle, then the relative positions of eccentric and main-pin would be as stated; but the link foot seldom extends so far down, and to correct the results of the angle so produced in its effect on the motion of the link and valve, the eccentric is set closer to the mainpin than go degrees; this point will be more clearly explained and illustrated later on.
The oscillating link of the Walschaért valve gear differs from the shifting link of the Stephenson type constructively as well as in the direction from which its curve radiates. Fig. 7a illustrates a style of the Walschaert link that approximates the standard type that has been adopted by locomotive builders in this country, and is used, with only such variations as variance in the general engine design may render necessary, by the American Locomotive Company on all of their engines equipped with the Walschaert gear at this time, exactly as shown in the plate.
While the Stephenson link is an open, one-piece affair, and is simple in construction, suspended by a pin in the link-saddle on one side only, it is usually considered necessary for the Walschaert link to be supported by a trunnion on each side as a furtherance of stability. In Fig. 7a, the piece that forms the link is shown in side elevation A as ia, and in end view B as ib, and is forged from wrought iron that is afterward case-hardened. Referring to view B, the
two bracket pieces 2b are shown to be bolted to the link piece, one on each side, their edges apparent in section A as 2a, where they widen out to cover the link, although the central spread is to strengthen that part of the bracket which is the frame work of the link. These link brackets are cast steel, and each piece includes in its casting a trunnion, 3b, in its exact centre, around which is pressed a case-hardened,
wrought-iron bushing; it is by these fulcrum-pins, or trunnions, that the link is suspended from a fixed point. At the lower extremity of the link piecethe link foot—is a pin hole, 4a and 4b, to receive the pin that connects the eccentric rod with the link, and this hole is fitted with a wrought iron bushing that is case-hardened. The reduction of the diameter of
these pins and pin holes from wear is but slowly effected if kept well lubricated, and is one reason why lost motion is so slow to develop in the Walschaert valve gear. Just above the pin hole 4a there is an oil well finished in the top of the link foot, 1 inches in diameter by 14 inches deep, with a 1-inch hole drilled down from the bottom and through the bushing of the eccentric rod pin hole for the feed of the oil; a threaded cap nut is screwed into the top of the oil well as a cover.
In section A the dotted arc lines 6a show the outlines of the opening, or slot, in the link in which the linkblock travels, and the faces of this link-slot is kept lubricated from an oil well in the top end of the link piece, this oil well being shown in dotted lines at 5a and 5b; it is covered by a cap nut that is a mate to the cover of the other oil well in the link foot, and has a threaded tap 1 inches in diameter. In section B, the left side of the link is turned to the outside of the engine, and the hole in the outside bracket at 7a and 7b is to permit direct oiling of the link.
The link-block is represented in sections C and D; C is the side view and shows the block in the position in which it would lie in the view A of the link,— imagine the link-block C raised, following the arc of the link until it entered the slot shown by the dotted lines 6a. Taking an end view, if the link-block, as shown in the section D, should be placed in the slot of the link piece of section B, it would be seen that its edges were almost flush with the sides of the link piece-extending only 3 inches out from each side of the link. It will be seen that the link-block contains an oil well, shown by the dotted lines at 9c and 9d, 1 inch in diameter by 14 inches deep, with a 4-inch feed hole from it down to the link-block pin.
The radius rod lies in an exact line with the link, but at its union with the link the radius rod is forked, its jaws passing, one on each side of the central link piece, and inside of the bracket sections at 00. There is a pin hole through each jaw of the radius rod by which it is connected to the link-block, the pin that passes through the radius-rod jaws also going through the hole 80, 8d, of the link-block, and this hole is supplied with a case-hardened, wrought-iron bushing as a protection against wear; but there will be no wear to the holes through the jaws of the radius rod for the reason that a bolt runs down through a hole in each jaw and through the link-block pin, thus holding the pin rigid with the radius rod and turning only in the hole through the link-block. The openings 7a, 7b, in the outer link bracket, besides giving access to the link slot for oiling, may also be used as an aperture through which the link-block pin can be removed.
Certain types of engines are so constructed that the eccentric rod is not in line with the link and cannot be