emergency application over that obtained 50-car train. The release after an emerby a full service application? A.-About twenty per cent. 46. Q.-How long a time is required to apply the brakes on a 50-car train in emergency application and how does it affect the release? A.-It requires less than three seconds to apply the brakes in the emergency on a gency application is obtained in exactly the same manner as after a service application, but it requires a longer time owing to the high pressure remaining in the auxiliary reservoirs and to the lower brakepipe pressure, as compared with a fairly heavy service reduction. MOVEMENT OF TRAINS Two New Rulings. By G. E. COLLINGWOOD second answer. Now and then train Two inquiries respecting practice un- rules are given an interpretation which der the Standard Code of Train Rules adds complication and serves no good The above ruling is one of have been submitted to the American purpose. Railway Association and replies made those unfortunate interpretations. thereto, as follows: "Question.-A train scheduled from cur in Rule 4, under a constructive in A to D is detoured over a foreign road from B to C, these stations being intermediate the schedule being annulled between B and C, can the train resume its schedule at C on its return to its home road, or must an order be issued to enable it to do so? "Answer.-Form K, providing for the annullment of a regular train, states that the train annulled loses both right and class between the stations named, and must not be restored under its original number between those stations. The words, "day of leaving" which oc terpretation are held to mean and refer to the date on which the schedule is due to leave its initial station with respect to the train which is then on the road at the time of change of time-tables. This interpretation provides that the dates of the old and the new scehdules shall correspond, which furnishes clear and constructive action for all concerned. This has been the practical interpreation since 1906 when the rule was Therefore, it is apparent that beyond put in effect. One of the weak points of the stations named in the annulling or old Rule 4, the one in use prior to 1906, der, the train retains both right and was that it failed to take any notice of class, and, therefore, immediately upon the date of a schedule. This fact returning to the home road, can proceed caused much misunderstanding and finalon its original schedule without further ly caused the rule to be entirely disorders to that effect." "Question. What is the meaning of the words, day of leaving' in Standard Rule 4? credited. A condition of this kind requires rulings without substantial rule support. After the present Rule 4 was adopted, one of the committee, who assisted in framing the rule assured the writer that the date question, as well as all other points of difference, had been settled by the new rule, but if the present ruling is adopted by roads it means "Answer. The words, 'day of leaving' refer to the heading of the column where, under the number of the train usually appears the wording, 'daily' or 'daily, except Sunday,' etc. Unless a schedule on the preceding time-table corresponds so far as this heading is concerned with a schedule of the new time- a quick return to misunderstanding and table it cannot retain its train orders and assume the schedule of corresponding number on the new time-table." questionable procedure. The ruling simply adds a new complication in the matter of a new correspondence, that of The first question is answered strictly "days of the week on which a schedule in accordance with standard rules and is in effect," without adding one iota of commends itself to practical railroad value to the rule in the way of safe and men, but the same cannot be said of the efficient operation. The point involved by this ruling is one which took care of itself, while the date, the real test of the rule and the vital point to be considered from any angle, is now left to inference, or guess-work. The mean ing which the committee has attempted to attach to the words, "day of leaving," were clearly taken care of by the general rule of schedule validity. If the ruling did nothing more serious than this it could not be severely criticised, but it has a far more serious effect, that of robbing the rule of all reference to date correspondence. what they say and say what they mean, but unfortunately this ruling if accepted will make the rule mean something which it does not say. Note the wording of the rule is singular, "day of leaving," and the writer is certain that the framers of the rule did not intend that the wording should be given such an impotent interpretation. Until such time as the wisdom or necessity of the ruling can be shown, the writer will stand by the practical interpretation which will preserve the rule as a practical one and not add complicaTrain rules are supposed to mean tions to an already over-worked rule. and Answers Questions and The Westinghouse Air Brake. 1068. Air Compressor Groans."What causes the 9-inch pump to groan upon reaching the maximum pressure? It works ail right until the last few strokes, then it seems as though it was laboring under strain, making a chattering groan."-R. G. Answer. The condition referred to is where the governor diaphragm valve begins to admit air above the governor piston soon after any pressure is accumulated. It will occur with the SF type if the feed valve pipe connection is cut off, as would be necessary if this pipe were broken and plugged, because there would be no air pressure above the Answer. Where pressure is the same the diaphragm to aid the excess pressure friction increases as speed decreases and spring (limited to about 25 pounds) in is greatest at rest. Therefore, where resisting the upward pressure of the the speed is considerable between two main reservoir air under the diaphragm. dry surfaces that are being pressed to- This condition would also obtain with gether the resultant resistance is low, any type of governor if dirt under the compared with that at low speeds. This diaphragm valve or low adjustment of will be noticeable with any dry bearing on an engine or a car, the tendency to squeal or groan developing at the lower diaphragm valve will be more noticeable speeds. If the parts in contact can vibrate, as is sometimes observed with driver brakes, the sound will be a chattering squeal or groan. The cause of the trouble with the compressor in question is insufficient lubrication of one or both of the main pistons or their rod, possibly augmented by abnormal pressure. With the piston rod this excessive pressure can be caused by the stuffing box packing. If the latter is of a solid type, has become hard and has then been tightened, as to stop blowing, it will often press much harder on one side of the rod than on the other and thereby cause the undue pressure. A design of metallic packing having a strong wedging tendency is very liable to cause this action when dry. Where the trouble is in the stuffing boxes the groaning is more probable near the completition of the up-stroke. If a solid packing is used have it replaced, the air end first as it is more liable to get hard than the steam end. A thick, close fitting and well oiled swab on the rod is a requisite for good results. Where compressor must work hard to maintain the pressure the air end requires a little valve oil more frequently than is usually given it unless it can be supplied from the cab, as with the attachment to the main lubricator that is now on many locomotives. a the regulating spring kept the valve open at low pressure. The effect of a leaky if the governor vent port is choked, as with accumulated gum, as this prevents the escape of air admitted above the piston. With air admitted above the governor piston the tendency is to at once close the governor steam valve and stop the compressor, but to close this valve the air pressure, acting downward on the governor piston, must overcome the combined upward pressure of the spring under the piston and the steam pressure that is acting to force the steam valve open. Therefore, as the air pressure increases it will gradually. force the steam valve nearer to its seat and thereby reduce the compressor speed. At what amount it will limit the air pressure will depend on the steam pressure carried, the size and type of the compressor and on the amount of air required to supply the train, but will usually be along about 40 or 50 pounds. 1070. Relation of Pressure and Volume.- "Please explain the relationship between pressure and volume."-R. G. Answer.-Referring to air, the brief way of stating it is that they are inversely to each other, temperature remaining the same. To illustrate, assume a compressor air cylinder with the piston at the top of its stroke, that its packing rings are absolutely air-tight, that below the piston the cylinder is filled with 1069. Why Defective Governor Cause "free" air, meaning that at atmospheric Low Pressure. "Please explain why a pressure, and that the lower receiving pump will stop after about 50 pounds and discharge openings are plugged and of air pressure have been obtained? I air-tight. If the piston is then forced understand that a leaky pin valve in or down until the volume is one-half of what leaky feed valve pipe connection to the SF governor is the cause of it, but why it was the pressure will have raised to 2/1, does it stop at 40 or 50 pounds?"-R. G. or twice as much as before, assuming farther that we wait until the heat resulting from the compression is lost and the air thereby cooled to its temperature before compression. Pressures are designated as gauge and absolute. The first is that shown by an ordinary gauge and is the amount above atmospheric pressure. Absolute pressure is the amount above a vacuum. As atmospheric pressure at the sea level is 14.7 pounds, adding this to gauge pressure will give absolute pressure, and taking it from absolute pressure will give gauge pressure. Where approximate results are wanted atmospheric pressure is usually assumed to be 15 pounds, and we will so consider it. With the piston at the top of the cylinder there was atmospheric pressure below it, or 15 pounds absolute. Hence, with one-half the volume at mid-stroke and twice the pressure the latter is 30 pounds absolute or, subtracting the 15 pounds, 15 pounds gauge pressure. If the volume is reduced to one-eighth of the original amount the pressure will be 8/1, or eight times as great. This would mean eight times the 15 pounds atmospheric pressure or 120 pounds absolute, being 105 pounds gauge pressure. Reversing the operation, if the piston is now allowed to move up until the volume is doubled, or 2/1, the pressure will be one-half. Absolute pressure must be used as when compressing, so one-half of 120 pounds gives 60 pounds absolute or 45 pounds gauge. If, instead the smaller volume had been increased four times, or 4/1, the pressure would have fallen to one-fourth of 120, or 30 pounds absolute, being 15 pounds gauge. This leaves the piston at half-stroke and the pressure the same on expansion as in compression. We may either double the volume again, by allowing the piston to go to the top, or start from the smaller volume of oneeighth of the original, and let it return to the top, and the result will be the same. Twice the volume will mean one-half the absolute pressure of 30 pounds, being 15 pounds absolute and nothing gauge. Eight times the smaller volume will be oneeighth of 120 pounds, or 15 pounds absolute and nothing gauge. Temperature, though, must be the same after compression or expansion for the calculation to be accurate. Otherwise the effect of the change in temperature must be considered. Compressing heats the air, thus raising the pressure more, while expansion cools it, thereby farther reducing the pressure. 1071. Plain Triple Valve on Engine. "Why is a plain triple valve used on an engine?"-R. G. Answer. Because a quick action triple on the engine would too greatly increase the liability of undesired quick action. It would be nearer the brake valve than the tender triple is, and the latter, if quick action type, is more liable to produce undesired quick action than is a similar valve on a car. A quick action triple on the engine would have but one advantage over the plain type; namely, it would better insure desired quick action on the train in an emergency application made from the forward engine of a doubleheader. This can be equally well insured by a quick-action valve on each tender. Therefore, on the engine the expense and the annoyance would be greater with no appreciable gain otherwise. 1072. K Type Triple Valve Change. -"I observe that the quick recharge port j in the K triple valve has been omitted. The earlier style used to have this port in the slide valve, but the imWhat are the reaproved type has not. sons for omitting it?"-R. G. Like the change of the feed arrangement in retarded position (using a small groove in the face or seal of the piston, where it strikes against the slide-valve bush, instead of the abandoned, small port through the slide valve), this has simplified both manufacture and maintenance, desirable ends. 1073. Feed Valve Spring Tensions."What is the tension of the supply valve piston spring and of the regulating valve spring in a B-6 slide valve feed valve?" -R. G. Answer. The writer has not available the tension of these springs with each in place and extended as far as possible, but assumes that the information sought has to do with the bearing of the spring tension on the proper operation of the valve, which is as follows: The regulating valve spring tension is gine is a 2-6-0 type, equipped with plain insignificant, considering the power of automatic brake, G-6 brake valve and the diaphragm with even a slight difference in the air and spring pressures on its two sides, but enough to insure that gum on the valve stems will not prevent the valve from seating when the diaphragm allows it to. old style plain triple. It carries 70 and If The effect of the tension of the piston spring is shown, on an accurate gauge, by Answer. First we must determine the difference between the two hands, whether the auxiliary reservoir charges when, with the automatic brake valve in properly. Ordinarily this can be asrunning position, the pressures are being certained by opening its bleeder after it "pumped up" at moderate speed on a has had ample time to charge fully, notlight engine. With the earlier slide valve ing first whether the sound indicates full feed valves, B-3 and B-4, respectively pressure and, after the pressure has got single and duplex, this difference is about as low as it can (brake valve in running 7 or 8 pounds, meaning that the main position and compressor working) obreservoir pressure must be that much serving whether the continued flow is as above the brake-pipe pressure to keep the rapid as a clean feed groove should give. piston spring compressed and the feed A sure test is to temporarily apply a valve open. With the improved type, gauge in place of the bleeder and note C-6 for the single-pressure and B-6 for the results in charging and in applying. the duplex, about 12 pounds is required. If the brake does not charge properly One effect of this stronger spring with find whether it is due to some obstructhe B-6 and C-6 valves is to insure more tion in the triple valve or its branch pipe prompt closing, when full brake-pipe pres- or to leakage from its auxiliary resersure is attained, where the parts are voir. It will be one or the other. But dirty. The other is that not less than 20 even without this preliminary work pounds excess pressure should be carried simple test may show that the fault is to insure correct operation, where 15 not in the triple valve or auxiliary respounds would be adequate with the older ervoir. The latter is assumed to be the valve. The margin of 7 or 8 pounds over right size for the brake cylinders. For the amount necessary to open either valve 10-inch, is to care for slight errors in adjustment of feed valves and errors in gauges. To illustrate the latter, if 20 pounds excess pressure is indicated in running position, but in release position and pressures fully equalized, quickly accomplished on a light engine, the red hand on the gauge stands 4 pounds above the black one, the actual excess pressure carried is but 16 pounds. 1074. Feed Valve Lubricant.-"Which lubricant is best to use in a feed valve, oil or dry graphite?"-R. G. Answer. This has not been determined conclusively, but theory indicates dry graphite, employed sparingly. If oil is used very little should be applied, and that only to the face of the slide valve and on the top of the bush where the slide-valve spring bears. Much oil on the piston, or even a little oil where the fit is as good as when the valve is new, will prevent prompt closing and thereby tend to overcharge with a short brake pipe, as with a light engine. 1075. Driver Brake Trouble.-"Please explain through the columns of the Magazine why the driver brake will not set less than full service application, either with or without a train. The en a 12-inch or 14-inch diameter cylinders this reservoir should be 33 ther for the defect as this shows that The common cause is brake cylinder leakage. Where this is serious the air can escape fully or almost as fast as it is admitted. If almost as fast a pressure will gradually build up and an application will be had after a heavy reduction. |