151. Q. On what is this type of triple valve designed to operate?
A. On freight equipment cars only.
152. Q. Explain the operation of the "K" triple valve.
[Ill.u.s.tration: Fig. 13. Full Release and Charging Position.]
A. When air is admitted to the brake pipe it is free to enter the triple at "a" (see Fig. 13) and flow through the pa.s.sage "e" to chamber "f", thence through port "g" to chamber "h" in front of the triple valve piston 4. Pressure forming in chamber "h" will force the piston to the left until its packing ring uncovers the feed groove "i" in the bushing, thus creating a communication between chamber "h" and the slide valve chamber. Brake pipe air will now be free to flow past the piston to the slide valve chamber and out at "R" to the auxiliary reservoir. Air will continue to feed through the groove "i" until the auxiliary reservoir and brake pipe pressures are equal, and it is then we say that the brake is fully charged. Brake pipe air entering chamber "a" will lift the check valve 15, and charge chamber "Y" to brake pipe pressure. When a gradual reduction of brake pipe pressure is made, as in a service application of the brakes, the pressure being reduced in chamber "h", auxiliary reservoir pressure will move the piston 4 toward service position. (See Fig. 14.) The first movement of the piston closes the feed groove "i", thus closing communication between the auxiliary reservoir and the brake pipe, preventing a back-flow of air from the auxiliary to the brake pipe, and at the same time moving the graduating valve 7, opening the service port "Z" in the slide valve. The continued movement of the piston will move the slide valve until the service port "Z" registers with the brake cylinder port "r" in the valve seat, thus creating a communication between the auxiliary reservoir and the brake cylinder. Air will now flow from the auxiliary to the brake cylinder until the pressure on the auxiliary side of the piston 4 becomes slightly less than in the brake pipe, when the piston and the graduating valve 7 will move back just far enough to close the service port "Z", thus closing communication between the auxiliary reservoir and the brake cylinder. At the same time, the first movement of the graduating valve connects the two ports "o" and "q" in the slide valve through the cavity "v" in the graduating valve, and the movement of the slide valve brings port "o" to register with port "y" in the slide valve seat, and port "q" with port "t". This permits the air in chamber "Y" to flow through port "y", "o", "v", "q", and "t", thence around the emergency piston 8, which fits loosely in its cylinder, to chamber "X" and the brake cylinder. When the pressure in chamber "Y" has reduced below the brake pipe pressure remaining in chamber "a", the check valve 15 is raised and allows brake pipe air to flow past the check valve and through the ports above mentioned to the brake cylinder.
[Ill.u.s.tration: Fig. 14. Quick Service Position.]
The size of these ports are so proportioned that the flow of air from the brake pipe to the top of the emergency piston 8, is not sufficient to force the latter downward and thus cause an emergency application, but at the same time takes enough air from the brake pipe to cause a local reduction of brake pipe pressure at that point, thus a.s.sisting the brake valve in increasing the rapidity with which the brake pipe reduction travels through the train. The triple valve is now said to be in "Quick Service" position. (See Fig. 14.)
153. Q. Will the triple valve move to quick service position whenever a gradual reduction brake pipe reduction is made?
A. No; with short trains, the brake pipe volume being comparatively small, will reduce more rapidly for a certain reduction at the brake valve than with a long train. Therefore, with a short train, the brake pipe pressure reducing more quickly, the triple piston and its valves will move to "full service" position, as shown in Fig. 15. In this position the quick service port "y" is closed, so that no air flows from the brake pipe to the brake cylinder. Thus, when the brake pipe reduction is sufficiently rapid, there is no need for this quick service reduction, and the triple valve automatically cuts out this feature of the valve when not required.
154. Q. How long will the auxiliary reservoir air continue to flow to the brake cylinder?
A. Air will continue to flow to the brake cylinder until the pressure on the auxiliary side of the triple piston becomes slightly less than that on the brake pipe side, when the piston 4 and the graduating valve 7 will move to the left until the shoulder on the piston stem strikes the slide valve. (See Fig. 16.) This movement has caused the graduating valve to close the service port "Z", thus cutting off any further flow of air from the auxiliary to the brake cylinder and also port "o", thus preventing any further flow of air from the brake pipe to the brake cylinder. The triple valve is now said to be in lap position.
155. Q. How is the triple valve affected by a further reduction of brake pipe pressure?
[Ill.u.s.tration: Fig. 15. Full Service Position.]
A. A further reduction of brake pipe pressure will cause the triple piston 4 and the graduating valve 7 to again move to the right, opening ports "Z" and "o", allowing a further flow of brake pipe and auxiliary air to the brake cylinder. This may be continued until the auxiliary reservoir and brake cylinder pressures become equal, after which any further reduction of brake pipe pressure is only a waste of air. With seventy pounds brake pipe pressure, and eight-inch piston travel, a twenty-pound reduction will cause equalization at about fifty pounds.
[Ill.u.s.tration: Fig. 16. Lap Position.]
156. Q. Explain the operation of the triple valve in the release of the brake.
A. To release the brakes and recharge the auxiliary reservoirs, air is admitted through the brake valve to the brake pipe. This increase of pressure on the brake pipe side of the triple valve piston 4 above that on the other side causes the piston and slide valve to move back to release position, which permits the air in the brake cylinder to flow to the atmosphere, through the exhaust port of the triple, thus releasing the brake. At the same time, air from the brake pipe flows through the feed groove "i" around the triple piston to the auxiliary reservoir, which is thus recharged. Now the "K" triple valve has two release positions: =Full Release= and =r.e.t.a.r.ded Release=. To which of these two positions the parts will move when the brakes are released, depends upon how the brake pipe pressure is increased. It is generally understood that those cars toward the head end of the train, receiving the air first, will have their brake pipe pressure raised more rapidly than those in the rear; thus the friction of the brake pipe causes the pressure to build up more rapidly in the chamber "h" of the triple valve toward the front end of the train than in those in the rear. As soon as the pressure is enough greater than the auxiliary reservoir pressure to overcome the friction of the piston, graduating valve and slide valve, all three are moved toward the left until the piston stem strikes the r.e.t.a.r.ding stem 31, which is held in position by the r.e.t.a.r.ding spring 33.
Where the rate of increase of brake pipe pressure is slow, it will be impossible to raise the pressure in chamber "h" sufficiently to overcome the tension of the r.e.t.a.r.ding spring 33, and the triple valve will remain in full release position, as shown in Fig. 13. Brake cylinder air will now be free to exhaust through port "r", large cavity "n" in the slide valve and port "p" leading to the atmosphere. If, however, the triple valve is near the head end of the train, and the brake pipe pressure builds up more rapidly than the auxiliary can recharge, an excess of pressure will be obtained in chamber "h" over that in the auxiliary reservoir, and will cause the piston 4 to compress the r.e.t.a.r.ding spring 33, and move the triple valve parts to r.e.t.a.r.ded release position as shown in Fig. 17.
157. Q. What effect has r.e.t.a.r.ded release position of the triple valve on the release of the brakes?
A. In this position of the triple valve, cavity "n" in the slide valve connects port "r" leading to the brake cylinder, with port "p" to the atmosphere, and the brake will release; but as the small "tail port"
extension of cavity "n" is over exhaust port "p", the discharge of air from the brake cylinder is quite slow.
[Ill.u.s.tration: Fig. 17. r.e.t.a.r.ded Release and Charging Position.]
158. Q. What is the object of delaying the exhaust of the brake cylinder air?
A. In this way, the brakes on the front end of the train require a longer time to release than those on the rear. This feature is called =r.e.t.a.r.ded release=, and although the triple valves near the locomotive commence to release before those in the rear, yet the exhaust of air from the brake cylinder is sufficiently slow to hold back the release of the brakes at the front end of the train long enough to insure a uniform release of the brakes on the train as a whole. This permits of releasing the brakes on very long trains at low speeds without danger of damaging train.
[Ill.u.s.tration: Fig. 18. Emergency Position.]
159. Q. What other desirable feature is found in this position of the triple valve?
A. In this position, the back of the piston is in contact with the end of the slide valve bush, and, as these two surfaces are ground to an accurate fit, the piston makes a tight "seal" on the end of the bush except at one point, where a feed groove is cut in the piston to allow air to pa.s.s around the end of the slide valve bush into chamber "R" and the auxiliary reservoir. This feed groove is much smaller than the feed groove "i" in the piston bush, so that when the triple valve piston is in =r.e.t.a.r.ded Release= position the recharge of the auxiliary reservoir takes place much more slowly than when it is in =Full Release= position, thus permitting a greater volume and pressure of air to flow toward the rear of the train.
160. Q. Explain the operation of the triple valve in emergency position.
A. When any sudden reduction of brake pipe pressure is made below that in the auxiliary reservoir, it will be felt in chamber "h" in front of piston 4 and cause this piston to move to the extreme right, as shown in Fig. 18. This movement of the parts will open port "t" in the slide valve seat and allow air from the auxiliary reservoir to flow to the top of the emergency piston 8, forcing the latter downward and opening emergency valve 10. The unseating of the emergency valve allows the air in chamber "Y" to escape to the brake cylinder, thus permitting brake pipe pressure in chamber "a" to lift the check valve 15 and flow to the brake cylinder through chambers "Y" and "X", until brake cylinder and brake pipe pressure nearly equalize, when the check valve is forced to its seat by the check valve spring 12, preventing the air in the cylinder from escaping back into the brake pipe again. The emergency valve and piston will now return to their normal position. At the same time port "s" in the slide valve registers with port "r" in the slide valve seat, and allows air from the auxiliary reservoir to flow to the brake cylinder. This sudden discharge of brake pipe air into the brake cylinder has the effect on the next triple valve, which in turn vents brake pipe air that affects the following triple valve and so on throughout the train.
NEW YORK AIR BRAKE
AIR COMPRESSOR
161. Q. What do Figures 19 and 20 represent?
A. These are cross-sectional views of the New York compressor.
162. Q. Of what does the valve gear of this compressor consist?
A. Of two main valves, actuated by tappet rods which enter into the hollow piston rods, and are moved by tappet plates, which are fastened to the steam piston heads.
163. Q. How is the admission and exhaust of steam controlled?
A. The valve under the cylinder at the right controls the flow of steam to and from the cylinder at the left; while the valve under the cylinder at the left controls the flow of steam to and from the cylinder at the right.
164. Q. Explain the operation of the steam end of the compressor.
[Ill.u.s.tration: Low Pressure Piston Moving Upward. High Pressure Piston at Rest. Fig. 19.]
A. a.s.suming both pistons are at the bottom of their cylinders, when the compressor throttle is opened, live steam will flow to both steam chests "B" (see Fig. 19), and through port "o" to the under side of the piston "T" and through port "g" to the upper side of piston "H". The steam under piston "T" will force it upward, and when it very nearly completes its stroke, the tappet plate "Q" will engage the b.u.t.ton on the end of the tappet rod "P", moving the main valve "C" to its upper position. In this position the exhaust cavity "r" in the main valve connects port "g"
with the exhaust port "X", thus allowing steam above the piston "H" to escape to the exhaust, at the same time steam is admitted through port "s" to the under side of piston "H", forcing it upward. As this piston very nearly completes its stroke, the tappet plate "L" (see Fig. 20) engages the b.u.t.ton on the tappet rod "P", moving the main valve "A" to its upper position. Exhaust cavity "r" now connects port "o", which leads to the lower end of the cylinder at the right, with the exhaust port "X", thus allowing the steam under piston "T" to escape to the exhaust, at the same time steam is admitted through port "V" to the upper end of the cylinder at the right, on top of piston "T", forcing it downward; as it very nearly completes its stroke, the tappet plate "Q"
engages the shoulder on the tappet rod "P", moving the main valve "C" to its lower position. The exhaust cavity "r" in the valve now connects port "s" with the exhaust port "X", allowing steam below piston "H" to escape to the exhaust, and at the same time steam is admitted to the top of this piston, forcing it down, thus completing a cycle of the compressor.
165. Q. Explain the operation of the air end of the compressor.
A. As the piston in the low pressure cylinder "D" moves up (see Fig.
19), a partial vacuum is formed below it, and air flowing through the strainer pa.s.ses downward through the air pa.s.sage, then past the lower receiving valve "W" into the lower end of the cylinder, filling it with air at about atmospheric pressure. In the meantime the air that is being compressed above the piston holds the receiving valve "U" to its seat, and lifts the upper intermediate discharge valve "K" from its seat, allowing the air to pa.s.s from the low to the high pressure cylinder "F".
The high pressure piston now moving up causes a partial vacuum to be formed below it, and air from the atmosphere flows past the lower receiving valve "N", filling this end of the cylinder with air at about atmospheric pressure. The air above the piston being compressed, holds the upper intermediate valve "K" and receiving valve "J" to their seats and lifts the upper final discharge valve "M", allowing the air to pa.s.s to the main reservoir. The action is the same on the down stroke, only air is compressed in the opposite end of the cylinders and the opposite air valves are used.
166. Q. What should be the lift of the different air valves?
A. In the No. 1 and No. 2 compressors all valves should have 1/16-inch lift; in the No. 5 and No. 6 all valves should have 3/16-inch lift.
167. Q. If a receiving valve to the low pressure air cylinder breaks or sticks open, what effect will it have on the compressor, and how may it be located?
A. No air will be compressed in the low pressure cylinder, as the piston moves toward the defective valve, and may be located by noting the movement of the low pressure piston, as it will be much quicker toward the defective valve than the opposite stroke. Air will blow back to the atmosphere as the piston moves toward the defective valve, and may be detected by holding the hand over the strainer.
168. Q. If an intermediate discharge valve breaks or sticks open, what effect will it have on the compressor, and how may it be located?