under his control by the duration of the brake-pipe exhaust.

The equalizing-discharge feature plays no part in making an emergency application, although in the emergency position of the brake-valve the equalizing-reservoir pressure is exhausted; in that position the brake-pipe air is discharged directly to the atmosphere through large ports in the rotary valve and seat, and this operation will be explained in reference to the rotary-valve charts to follow.

The arrangement of all ports in the rotary valve and seat, and air passages through the body of the brakevalve, should be thoroughly understood before proceeding further than Fig. 23, with the preceding piping diagrams for reference in remembering the pressure connections of the brake-valve.

The (brown) port, d, in the rotary-valve seat is directly connected with the feed-valve pipe, and the (yellow) port, c, with the brake pipe, and the flow of air from the former to the latter in the running position has been explained; the passages leading from ports c and d down to the pipe connections with the pipe bracket are shown in the dotted lines. The very small port, r, in the seat is drilled down to the atmospheric exhaust port, and when the brake-valve is in release position this warning port, r, is connected with port d by another port in the face of the rotary valve, and

the sound of the escaping feed-valve pressure indicates to the engineman that the brake-valve is not in the normal carrying position. Port u in the seat connects with the application-cylinder pipe. Port l in the seat connects with the distributing-valve release pipe, and in running position is in register with port h in the rotary valve, through which the application cylinder of the distributing valve has temporary connection with the atmosphere via the large, central ports, o and EX, in the rotary valve and seat, respectively. The small (red) port, p, in the rotary-valve seat, quite close to the large, central port, EX, leads downward and out to the connection with the pipe to the diaphragm-valve chamber of the excess-pressure governor top; it is given the red color because in release, running and holding positions it receives main-reservoir pressure through port s, which is drilled through the rotary valve and has an extended cavity in the valve face through which the connection in the several positions is maintained.

Of the ports in the rotary valve not yet alluded to, a is cut clear through the valve, and in release position is located directly over port b in the seat, permitting main-reservoir air from over the rotary valve to flow into the large passages to the brake pipe by exactly the same route, from port b onward, as was taken by the feed-valve pressure in running position. Port x is a large opening in the face of the rotary valve, with a wide,

shallow cavity cored out of the interior of the valve -fan-shaped, as indicated by the dotted lines-that reaches inward to the central exhaust port, o; when the brake-valve is in emergency-application position the facing port, x, is in register with the direct brake-pipe port, c, in the seat, this connection providing the heavy discharge of brake-pipe pressure to the atmosphere that insures quick action of the brakes. Port j goes through the rotary valve, and in release position registers with port g in the seat so that main-reservoir air will be temporarily supplied to chamber D and provide a holding-down pressure above the equalizing piston as great as the pressure flowing to the brake pipe beneath it.

As stated, port k is a cavity in the face of the rotary valve, but it has a thin, fan-shaped extension cored in the interior of the valve, shown by dot-and-dash lines, that connects with the small port, n, and the latter is widened and lengthened to form a larger cavity in the face of the rotary valve; when the brake-valve is in emergency position the facing cavity of port n connects with port u in the seat, the end of cavity k has connected with the narrow extension of the feed-valve port, d, in the seat, and port j is lying over port d; through this combination of ports main-reservoir pressure, entering port j at the top of the rotary valve, finds a connected passage to the application cylinder of the distributing valve as the maintaining pressure heretofore alluded to.

These last-mentioned ports have been somewhat changed in configuration in the rotary valves of more recent manufacture, but simply as an improvement in detail, and the maintaining-pressure supply remains unchanged. In the following representations of the rotary valve in its several positions the newer arrangement of those ports will be used, as the later design is easier to understand.

THE ROTARY VALVE.-The six plates that follow are plan views of the rotary-valve seat of the H-6 brakevalve, seen through a transparent rotary valve in its six operating positions. The gray tint represents the ROTARY VALVE, and the ports that are cut vertically through it from top to face show the ROTARY-VALVE SEAT as plain white. All ports and passages in the ROTARY VALVE are indicated in red outline; those that are cut clear through are in continuous red lines; red, dotted lines show ports and cavities in the face of the rotary valve; and red dot-and-dash lines indicate ports and cavities in the interior of the rotary valve. Ports and cavities in the ROTARY-VALVE SEAT are in black outline, the dot-and-dash lines indicating cavities below the surface of the seat.

Reference numbers and letters are avoided as far as possible in these transparencies; the names of the several ports in the rotary-valve seat are printed plainly thereon, but no words, figures nor letters appear in

connection with the ports in the rotary valve, to prevent confusion, and further the appearance of its transparency; it is to be presumed that the student has already become familiar with the appearance and positions of these ports, and their names or reference letters; however, in the following explanations of the several positions of the rotary valve, when its ports may be alluded to by reference letters that have not been memorized, the student is referred back to Fig. 23. The rotary-valve handle is of the same gray color that represents the rotary valve, with red outline, and its operative positions are indicated by the six radial lines with the words release, running, holding, lap, service, and emergency.

In Fig. 25, as the handle shows, the rotary valve is in Release Position. The two large ports in the rotaryvalve seat worded "to brake pipe" are connected by a large cavity beneath the surface, indicated by the broken, black lines in half circles, with the brake-pipe connection directly beneath the right-hand port; the large port that opens vertically through the rotary valve is now in exact register with the left-hand brake-pipe port in the seat, and as main-reservoir pressure is always present on the top of the rotary valve, its route in flowing directly to the brake pipe is plainly traced. The equalizing reservoir is also receiving main-reservoir pressure, as port j that goes through the rotary