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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

Rotary Valve. Release Position

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

valve is directly over the port to chamber D in the seat; port j is extended as a short cavity in the face of the rotary valve, in order that main-reservoir pressure

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Copyright, 1909, by The Norman W. Henley Publishing Co.
Fig. 25.—H-6 Brake-Valve. Top view of transparent rotary valve,

and plan view of rotary-valve seat. Release position.

will continue to feed to chamber D when the brakevalve handle is moved toward running position, as

Rotary Valve. Release Position

long as the same pressure is flowing to the brake pipe —these are the equalizing ports. Port s is the third and smallest of the three that are cut through the rotary valve vertically; it lies to the left of and very close to the large, central exhaust cavity, with a connecting groove in the face of the rotary valve, the farther end of which in this position overlies the port in the seat that leads to the pipe connection with the excesspressure head of the pump governor, and supplies the main-reservoir pressure that controls the action of the pump while the brake-valve handle is in release position. The very large cavity, f, in the face of the rotary valve now covers the feed-valve port in the rotary-valve seat, and overlaps a greater area of the seat that includes the warning port through which the feed-valve air discharges into the atmospheric outlet of the large, emergency exhaust port, giving warning of the possibility of brake-pipe overcharge.

Except for this connection with the warning port, in release position of the brake-valve the feed-valve pipe is blanked against any delivery of its air; and in case the feed valve leaked through-never so slightly —the feed-valve pipe would accumulate a pressure in excess of 70 pounds possibly main-reservoir pressure —which would prevent the excess-pressure top of the governor from closing-off steam from the pump; this would be particularly undesirable in descending

heavy grades, when it is sometimes desired to charge the train line to 90 pounds by leaving the brake-valve in release position. Any leak through the feed valve that would not be manifest in running position, however, will be disposed of by the blow-off through the warning port.

In Fig. 26 the brake valve has been moved to Running Position, the large supply-port, a, and the equalizing port, j, in the rotary valve are now blanked on the rotary-valve seat, cutting off the direct flow of mainreservoir pressure to brake pipe and chamber D. The large, adjoining ports in the seat—" to feed valve," and "to brake pipe," have been brought into conjunction by the very large cavity, f, in the face of the rotary valve, through which the brake pipe is now being supplied with air from the feed valve that limits it to 70-pounds pressure. The state of equalization of the brake-pipe and chamber-D pressures is still maintained: in this position, through cavity k in the face of the rotary valve, which connects the right-hand brakepipe port in the seat with port g, also in the seat, that is worded—“to chamber D.In this, the latest model of the H-6 rotary-valve, port k is in permanent connection with a twin, but somewhat smaller, port, n, by a narrow groove in the face of the rotary valve, providing the same service in a much simpler and easier understood manner than the former arrangement; port n, however,

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