stroke for both service and emergency application, and is extended to form a cylinder or shell in which piston 129 is fitted. Through piston 129 is a small opening F, allowing train pipe air to pass through and thus equalize the pressure on both sides. This opening is of such a size that when the main piston 128 moves slowly to the left, as in service applications, the air in space G will be pressed through the opening F without disturbing the piston 129 from the normal position shown.

Q.-649. But how will these parts act in an emergency application?

A. A sharp reduction of train pipe pressure for an emergency stop will cause main piston 128 to move rapidly to the left. In this case, air from space G cannot flow through passage F fast enough and exerts a momentary pressure upon piston 129 strong enough to overcome its resistance and cause valve 71 to be pushed from its seat. This allows train pipe air to enter the passage H and escape to the atmosphere through openings J and M, while at the same time it forces piston 137 to the right, which unseats valve 139 and allows the auxiliary reservoir pressure to rush almost instantly to the brake cylinder through the large passages K and L and check valve 117.

Q.-650. Will vent valve 71 stand open and exhaust all train line pressure? A.-No. As passage F is always open, the temporary pressure exerted by the air in chamber G has meanwhile rapidly lost its effect, and spring 132 has returned valve 71 to its seat, thus stopping the escape of air when train pipe pressure is sufficiently reduced to properly apply the brakes. As valve 71 closes it returns piston 129 to its original position, its travel in that direction being limited by the stop 142. (Valve 139 and piston 137 have also been returned to their former positions.)

Q.-651. How does the valve release? A.-Restoring the train pipe pressure above auxiliary reservoir pressure causes main piston 128, and with it, slide valves 38 and 48, to return to the positions shown in the sketch, allowing the auxiliary reservoir to be replenished through the feed groove and the air to escape from the brake cylinder to atmosphere, through the cavity in the slide valve, thus releasing the brakes.

Q.-652. The power, then, for both service and emergency applications in this triple, lies wholly within its auxiliary reservoir. In service application, the auxiliary reservoir pressure is sent gradually to the brake cylinder in such divided quantities as may be desired by corresponding reductions in the train pipe pressure; while in an emergency application, the emergency valves and larger passageways pass the auxiliary reservoir pressure almost instantly to the brake cylinder.

A. Yes; but while the emergency application is being produced as above described, the train pipe pressure is being

vented at each triple, actuating the following triple and causing quick serial application on all triples throughout the train.

Q.-653. Ports J and M. then, discharge train line pressure to the atmosphere, when vent valve 71 is suddenly and widely opened, thereby making a considerable train pipe reduction whose impulse is felt on the following car, and produces quick serial application throughout the train?

A. Yes. The quantity of train pipe pressure vented into passage H cannot escape through port M as rapidly as it enters the passage, so it pushes piston 137 to emergency application position, and port J is thereby made to offer additional exit capacity. The exit opening offered by ports M and J in emergency application make a sufficient reduction in train pipe pressure to actuate the following triple.

Q.-654. Then the duty of port M is to discharge sufficient train pipe pressure in emergency application to actuate the following triple?

A. Its only duty is to vent train pipe pressure from passage H to the atmosphere, which, with the assistance of that portion of pressure vented from port J, after it has forced piston 137 to emergency position, makes the desired reduc tion to throw the next adjacent triple into emergency.

Q.-655. Could not port J perform this work alone without assistance from port M?

A. Not satisfactorily. In the earlier form of this valve, port M was omitted; but experience proved that port J could not discharge train-pipe pressure in sufficient quantity to apply the brake and hold it on. The auxiliary reservoir pressure, in supplying the brake cylinder, would reduce lower than the pressure remaining in the train pipe, thus releasing the brake, which, as train pipe pressure continued to escape through engineer's valve, would reapply in the service. Port M, however, has sufficiently added to the exit capacity of passage H, that sufficient vent is now had and effective application is assured. Again, port M quickly carries off the train-pipe leakage past a defective vent valve which might otherwise push a tight or clogged piston 137 into emergency position.

Q.-656. After a light service application has been made, can the emergency application be had?

A.-No. As main piston 128 travels full stroke in both service and emergency applications, the pistons 128 and 129 have been closed together, pushing the pressure in space G out through port F, thus annulling an emergency application until after the train pipe has been recharged, pistons 128 and 129 separated, and space G refilled. Emergency application can only be obtained when the pistons are separated and space G filled. Otherwise, vent valve 71 cannot be forced off its seat.

Q.-657. Inasmuch that auxiliary res

ervoir pressure alone goes to the brake cylinder in both service and emergency applications, and no train pipe pressure, would not the full service be almost equally as effective as the emergency?

A.-No. The service is much slower, and the serial application being impossible in this case, the full service application would not be nearly as effective as the emergency.

Q.-658. If two or three non-venting triples are together in a train, will the venting of this triple carry the impulse through those cars to other venting triples beyond?

A. It is doubtful, and would depend largely upon the condition of the triples. Q.-659. What points should be observed in the maintenance of this triple?

A. The vent piston should be removed from the seat, middle portion of the valve case, known to repair men as vent valve seat, both pistons placed in a bath of light oil to cut the gum around packing rings, the rings worked with a light pressure with the finger until free in grooves and then, keeping plenty of light oil under the rings, turn them until all signs of dirt disappear. Clean the cylinders, feed grooves, slide valves and seats thoroughly, being careful to remove all lint left by cleaning cloth. Lubricate the slide valve seats with just enough oil to cover the surface, and the cylinder for the main piston with as much oil as will hang to its walls, without free oil in bottom of cylinder. Insert the piston, being very careful not to double up spring on back of main slide valve, and work the piston in its cylinder about twenty times. Then examine the ring carefully to see that it shows a perfect bearing on its circumferential surface, and if it does, turn the packing ring so that its opening will be somewhere in the bottom third of the piston and return the piston to its place. Lubricate the vent piston cylinder the same as the main cylinder. Clean port F with pointed match or toothpick, and attach the vent piston to the vent valve seat. Place the vent valve seat in position on triple valve body, and then push the vent piston into its cylinder. Clean all other parts of triple valve thoroughly without using oil, and put them together dry after replacing all defective rubber seats.

Q.-660. Might not the shell or extended cylinder on the main piston 128 be distorted or sprung out of round, causing piston 129 to bind, work jerky

and cause emergency application at all times, even when a service was desired?

A. Yes, careless and unskilled workmen have done this. Sometimes it is done by twisting and prying when taking the triple valve down, dropping the piston, and by awkardly catching the shell in a vise. Care should be taken in doing this work. The cap 126 and middle piece 130 should be lifted off carefully, and pulled straight out, thereby drawing out piston 129 without injury to itself or the shell cylinder. Care should be also taken in laying down the middle piece 130, not to bend the piston 129, which will then bind in the middle piece and in its shell cylinder, thus making applications uncer

tain and erratic.

watch in taking apart and cleaning the Q.-661. Are there not other points to triple?

A. Yes. As the cap 126 and middle piece 130 stick together when taken down, due to the rubber gasket between them, care should be taken in separating them, else the stem of piston 129 will be bent. Repairmen and cleaners should not hammer and twist on the cap to loosen it from the triple valve body, for this will tend to bend the piston, thus causing the triple to go into emergency when service application is attempted. In replacing the main piston and the slide valve care should be taken that the large slide valve has not been reversed. When in its proper position the cavity in the valve should be toward the piston end. Caps 119 and 141 and plate 127 should be securely fastened when replaced.

Q.-662. What would happen if cap nut 141 were not securely tightened or the emergency valve leaked?

A. It would leak away auxiliary reservoir pressure the same as a slightly opened bleeder cock in the auxiliary, and causes the brake to release.

Q.-663. Suppose the check valve leaked or the cap nut 119 were not securely tightened and leaked?

A. Brake cylinder pressure would leak away and reduce braking force as does a leaky leather piston packing in the brake cylinder.

Q.-664. Although it is not necessary to disconnect the train pipe to clean the operative parts of the triple, is it not advisable to disconnect and inspect and clean the strainer?

A. Yes. The improved drain cup in the train pipe has proved that it reduces the amount, but does not entirely exclude the dirt which usually finds its way to the triple valve.