The mechanical arrangements of this stoker include preparatory means, or crusher, at or near the back part of the reciprocating forwarding means, which are shown on the forward part of the locomotive tender in this illustration. The forwarding means are placed generally horizontal, being only raised sufficiently at the front to elevate the coal over the top of the receiving hopper, in the bottom of which the main feed plungers operate. The crushing mechanism also serves the purpose of a measuring and feeding device to prevent the overloading of the conveyor. It is timed in operation with the reciprocating forwarding means, and only permits a sufficient amount of coal to enter the back part of the conveyor as can be readily and without congestion carried forward in the normal operation thereof.

The conveyor is made up of sets of fingers carried on a frame. and hung from above the top of the trough; this frame is reciprocated forward and backward with considerable travel, so that the vanes or fingers, the bottom ends of which just clear the bottom of trough, serve to carry the coal forward and in the return stroke are lifted over the top of the coal which has just been moved toward the front end of the conveyor trough, and some of them in each set drop behind the coal below them, and in turn carry some more coal forward.

The coal, on reaching the forward end of the conveyor, drops into a hopper in the bottom of which are the main feed plungers, which operate in a substantial casting placed just under the backhead of locomotive boiler.

In the firebox are placed two heavy cast-steel fuel troughs, into the back part of which the feed plungers force the coal. At points spaced throughout the bottom of the fuel troughs are auxiliary plungers which serve to assist in forwarding the coal still farther forward. Small castings in the shape of fingers or teeth are placed adjacent to the outward end of the auxiliary pistons to assist in enlarging the end thereof, and serve as agitators to keep the coal moving forward in the feed troughs as the auxiliary plungers are operated.

This view will show the troughs more in detail and the grates at each side. In this drawing the grates are of the level form.

The Crawford stoker is operated by means of a steam cylinder attached to back end of locomotive frame on left side of locomotive, and is connected to the stoker mechanism through means of cross shaft with arms thereon to attach to the steam cylinder, the conveyor, the crushing mechanism, and the main and auxiliary feed plungers.

The method of firing is about as follows:

The reciprocating action of the crushing and conveying means brings the coal to the main feed hopper, and it is directed toward each feed piston by a ridge plate therein. Each main feed piston forces its portion of these charges into the back part of the main feed troughs in the firebox through openings in the casting underneath the mud ring.

In this operation any lumps of coal which are larger than these openings will, of course, be additionally broken up by a similar action to that of the main crushing and measuring piston. These charges of fuel, forced into the trough in this way, serve as forcing means to push the coal, already in the troughs, still farther along, where it is taken up by the auxiliary feed pistons, and at the same time some of it is forced over the sides of the troughs as it travels toward the forward part of the firebox. The troughs are usually

made with slight offsets in their widths which serve as abutments or partitions, similar to those described in the Barnum stoker, and these partially assist in lifting the coal up out of the troughs to the grate area. The forward end bottoms of the troughs are inclined upward, so that the small amount of coal which reaches the vicinity of the throat sheet is in turn lifted out of the trough on to the grate area in the front part of the firebox.

There are nearly four hundred of these stokers in actual service, certain divisions of Pennsylvania Lines West being completely equipped, and they have been in service for the past three or four years with such success that this stoker may be considered very properly as one of the possibilities for general application.

Having thus described the underfeed stoker which has so successfully demonstrated the correctness of the theory of that method of firing a locomotive, you will no doubt be interested in the next description, which is that of the Street locomotive stoker, of which more than one thousand are now in service on very large modern locomotives. It may very properly be considered as the principal representative of another method of firing; namely, that of supplying coal to the entire surface of the fire continuously at the rate of combustion, no coking periods being provided for as in the method just described.

Drawing showing general plan of Street locomotive stoker.

The modern locomotive is called upon to operate at widely varying rates of horse-power output, often from maximum to zero

within very short spaces of time, and this method of firing is based on the theory that there should be a given rate of combustion per square foot of grate area at any given time just sufficient to supply the steam output required of the locomotive boiler at that time; that is to say, there should be the same flexible control of the fire that there is of the throttle and cut-off.

This drawing will give you an idea of the general arrangement of the Street locomotive stoker, which consists of a conveying, elevating, and stoking mechanism.

This stoker is designed to handle only coal which will pass through a screen having openings not to exceed three inches square. A screen of this character is placed just below the bottom of coal pit of locomotive tender, and above this screen are placed movable slides, so that a portion only of the screen is exposed at one time. Below the screen is placed a conveyor trough in which is operated the forwarding screw of helicoid form, which serves to carry the coal forward to the receiving hopper which constitutes the bottom part of the elevating mechanism.

In the left-hand section of the drawing is shown the general elevating and driving mechanism of the stoker. The endless chain of elevator buckets is driven by a single-acting, high-speed engine built into the upper left-hand part of the elevator, as will be plainly noted on the drawing. This high-speed engine drives the endless conveyor through means of worm, worm wheel, and the usual arrangements of sprocket wheels placed at different points. No sprocket is placed at the upper right-hand section of the elevator casing, however, as it is necessary to drop this part of the casing to clear the locomotive throttle connections which are at this point on backhead of locomotive.

In the centre of upper section of elevator casing is placed the mechanism which apportions the coal to the different firing points by first screening out the smaller particles and directing them toward the middle firing means, as will be later described, and then equally, or unequally, as may be desired, dividing the coarser particles of coal and directing them toward the side distributers.

On the right-hand side of the drawing will be seen a crosssection of the backhead of locomotive giving a better view of the hopper at bottom of elevator and showing the downwardly directive feature of the center distributer; the purpose of this being to assist in directing the finer particles of coal or dust to a zone in the back

part of the firebox, where these small particles will be less apt to be taken up by the draft and carried away before they can be properly consumed.

One of the side distributers will also be observed which serves to direct the coal generally forward, and on the bottom of which are placed directing ribs which assist in spreading the coal over a fan-shaped zone on each side of firebox. Each of the side distributers directing the coal over a fan-shaped zone in this way serves to cover the main part of the grate area, overlapping slightly in the center of the firebox, leaving a small, triangular area at back of grate, which is covered by the finer coal directed there by the center distributer as just mentioned.

The distributers at the side and center are simply rough castings removable from the ends of the tubes which are placed in openings through backhead of locomotive boiler, and which permit their replacement when warped or destroyed by heat of firebox after their normal period of service.

Photograph of end view of assembled Street locomotive stoker.

This photograph of end view of Street stoker, assembled for exhibition purposes, will give you a better idea of the general arrangement, the view being directly toward the backhead of boiler.