VOL. 36 No. 5

Plate III-Duplex Pump (UpStroke of High-Pressure Piston).

Plate III of the New York Air Brake Series of the Locomotive Firemen's Magazine Educational Charts shows a sectional and perspective view of the duplex pump, with the high-pressure air piston making its up-stroke, and with the lowpressure air piston at rest at the upper end of its cylinder.

The colors used with this plate are red, indicating main reservoir; dark brown, indicating air pressure of about 45 pounds; orange, indicating atmospheric pressure; blue, indicating live steam; and light blue, indicating exhaust steam.

These are the same colors that were used in Plate II, and these same colors will be used for the remaining plates that show the duplex pump, and their significance will be the same, so that it will not be necessary again to state in the description what pressures these various colors indicate.

Glancing at the plate it will be observed that the low-pressure piston, at the upper end of its stroke, is being held stationary by the steam pressure underneath it in the low-pressure steam cylinder; that the tappet plate 1 D P 20 has engaged the button head on the end of the tappet rod 1 D P 7, and, glancing farther down into the steam valve chamber, it will be seen

MAY 1904

that the slide valve 2 D P 5, attached to the end of this tappet rod, has been moved upward.

The slide valve 2 D P 5, in the position shown, has uncovered the steam port leading from this steam chamber to the lower end of the high-pressure steam cylinder A, and has brought the steam port leading from the upper end of steam cylinder A into communication with the exhaust cavity in this slide valve, and the steam exhaust passage leading to the atmosphere; the arrows and light blue color indicate that the steam is exhausting from cylinder A, above the high-pressure steam piston, through the exhaust cavity in the slide valve, into the exhaust pipe and thence to the atmosphere.

The opening of the steam port leading to the lower end of steam cylinder A, and the opening of the steam port leading from the upper end of cylinder A, permits the live steam to enter cylinder A, under the high-pressure steam piston, and the exhaust steam to escape from above this piston; thus the live steam entering at the lower side can force the high-pressure steam piston, together with the air piston, upward. While the high-pressure piston is making its up-stroke the lowpressure piston remains stationary with live steam pressure underneath it.

Glancing at the air end of the pump, it will be observed that the lower air inlet valve 2 D P 9 and the lower intermediate

air inlet and discharge valve 2 D P 11 are raised from their seats, thus providing a passageway from the atmosphere into the lower end of the high-pressure air cylinder C, through which air from the atmosphere may flow to follow the high-pressure air piston and fill the vacuum which it forms in the high-pressure air cylinder, as it moves upward and as indicated by the coloring.

The air pressure in front of the highpressure piston is equal to that in the main reservoir; and the arrows, as well as the coloring, indicate the course which the air is taking as it is being compressed ahead of the advancing high-pressure piston and is being discharged through the upper final air discharge valve 2 D P 11 into the air discharge pipe and the main reservoir.

Upper intermediate air inlet valve 2 D P 11 is on its seat, and is held to its seat, as indicated, by main-reservoir pressure. This valve in the position shown prevents main-reservoir air from leaking back into the low-pressure air cylinder.

The upper air inlet valve 2 DP 9 is held upon its seat by gravity, and the pressure that remains in the air passage and clearance spaces above the low-pressure air cylinder.

The lower final discharge valve 2 D P 11 is held upon its seat by the main reservoir pressure, and by gravity, and prevents main-reservoir air from passing back into the lower end of the high-pressure air cylinder.

From this plate it will be learned that when the high-pressure piston is making its up-stroke and the low-pressure slide valve 2 D P 5 is in position to open the steam port leading from its chamber to the lower end of the high-pressure steam cylinder A, and to establish communication between the upper end of the highpressure steam cylinder and the exhaust port and passages leading to the atmosphere, that the high-pressure slide valve 2 DP 5 is in position to uncover the steam port leading to the lower end of the low-pressure steam cylinder, and to establish communication between the upper end of this cylinder and the exhaust port and passage leading to the atmosphere.

In the air end we learn that the lower air inlet valve and the lower intermediate air inlet and discharge valve are both raised from their seats, while the corresponding valves in the upper end of the pump are on their seats; that the upper final discharge valve is raised from its seat and the lower one is upon its seat.

Adhesive Weight of a Locomotive.

There is perhaps no more variable factor in locomotive design than that expressed by the word adhesion. It is so variable, in fact, and influenced by so many causes, that close calculation is necessary when an engine is in the drawingoffice stage. Among these elements that demand earnest attention, in order that close results may be attained, are increase of tractive force due to decrease of wheel diameter and increase of cylinder diameter by wear; and condition of the rail, whether dry, wet or greasy; and here climatic conditions must be considered. Arrangement of the wheels also exerts a wide influence in weight distribution, as in the case of engines having trailing truck wheels. The location of these wheels near to, or far from, the drivers, decreases or increases, respectively, the weight on the drivers, and therefore the adhesive weight. This fact has been ignored in some recent engines, and it has been found to operate to their serious disadvantage in starting a train.

In order to overcome this preponderance of weight on the trailing truck the equalizer with an adjustable fulcrum is sometimes used, by which the weight is varied to suit conditions, within narrow limits, except in instances when the traction increaser is used. The best examples of a fixed equalizer fulcrum on the Atlantic type of engines is found on the Pennsylvania E-3 class, where the wheel base of the trailing truck is of such length as to give an adhesion that holds the engine to the rail under maximum piston effort. This is the result of careful calculation, in which it is probable that actual, and not estimated, weights were used to locate the center of gravity of the engine. The effort of the long wheel base whereby the adhesive weight is increased, is to make a greater curve resistance, but this may be provided for in ordinary cases by lateral motion without resort to the radial devices sometimes employed.

In determining the wheel loads there can be no more unsatisfactory method than that of rough estimates of weights, as was made evident not so long ago in the design of a six-wheel switch engineone of the simplest possible problems of the kind, and involving only an equable distribution of wheel loads. Careless work in locating the center of gravity of the engine resulted in a wheel location that placed 6,000 pounds excess of load on one axle.

Of equal importance to the load distribution is the ratio of adhesive weight to tractive effort, but the impression is forced that the latter is of secondary importance, when practice is seen to follow no standard of proportions, but is shown to even transpose the ratios for freight and passenger engines. Instances are too numerous where new freight power has a ratio of adhesive weight to tractive force, of four and less, and passenger engines a ratio of five. Climatic conditions cannot be wholly responsible for such a palpably mixed state of things, which, if it resembles anything, looks very much like guess work.

The English designer knows how to approach the problem of wheel loads, and gives much attention to that feature of his power, more especially to the end that his load on drivers shall be close to the slipping point, rather than above it, preferring to sacrifice weight that is of questionable utility; and the reason for this is not all traceable to right-of-way restrictions. His engines are therefore never burdened with a load which is useless except at starting, but they seem to maintain their good name for efficient perform

ance.

This is seen in the latest examples of the English Atlantic type, built for the Northeastern Railway, and illustrated in London Engineering. These engines are practically the limit in size for that road, having 20x28-inch cylinders, and weighing 161,280 pounds, with 87,360 pounds on the drivers, and 36,960 pounds each on leading and trailing trucks. The ratio of adhesive weight to the 23,200 pounds of tractive effort is 3.76 to 1-which strikes one as representing some thought to the factors that make or mar the success of a locomotive.

The American Railway Master Mechanics' Association formulated some values a few years ago having direct bearing on these ratios, and they are on record in the proceedings of that body. It may not be out of place to say that they are of the same value as applicable to our power today that they were when presented to the association.-Railway and Engineering Review.

The Storage Air Brake System.

To the public at large there is no more important application of compressed air than the air brake. The safety and increased speed directly resulting from its use cannot be calculated. Its success in the operation of steam cars was naturally

followed by its application to street transit service, particularly after the rapid development of the electric street car. The conditions on the steam railway have so far precluded any storage air system. Steam is comparatively plentiful and the amount needed to operate a small air compressor is insignificant compared with the total amount generated. With the adoption of air brakes on the electric street car it was natural that the same general plan should be followed, the motive power, electricity, being utilized to operate a small air compressor. Conditions on a steam railway and street car line differ materially. The slower speed and the shorter trip of the latter make it possible to carry the supply of compressed air needed for one trip without necessitating a storage reservoir of impracticable size. This fact has been recognized for some time, but certain features of the subject have heretofore prevented the general adoption of the new system.

Special interest is shown therefore in the action of the St. Louis Transit Company, of St. Louis, Mo., in establishing a system of storage air brakes on all its The operation of this plant will be awaited with great interest, as its success or failure will have a great influence on the future equipment of the modern street railway.-Compressed Air.

cars.

Locomotive Draft.

The proper burning of fuel in a locomotive depends as much on the drafting of the engine as it does on the skill of the fireman and the co-operation of the engineer.

The steaming qualities of an engine in the front end arrangement, and a “poor may be entirely spoiled by a small change steamer" may be made into a "good steamer" in like manner. has been said about the proper way to A great deal fire an engine, but the drafting of the engine has received but little attention. In looking over the work book the report most often found is "Engine does not steam." This is crossed off at once, because it is impossible in most cases to locate the trouble without watching the burning of the fire.

The object of these papers is to give an explanation of locomotive draft that will enable firemen and engineers to make an intelligent report of all cases where an engine is improperly drafted.

The draft of a locomotive is the current of air passing through the firebox.

There is a direct passage of air through a locomotive from the atmosphere through the ash pan, grates, fire and firebox, through the flues and front end and out the stack. Exhaust steam from the cylinders passes through the exhaust passages in the saddle, through exhaust stand and nozzle and out the stack, the front end being so arranged that the exhaust will form a jet and will enter the stack somewhere near its base. This exhaust steam passing at high velocity through the front end and out the stack has a tendency to carry with it the air and gas in the front end in a manner somewhat similar to a train at high speed picking up dust and papers and carrying them along.

This emptying of the front end of air and gas simply means that the passage of exhaust steam from cylinder to stack reduces the front end pressure below atmospheric pressure, or, in other words, creates a vacuum in the front end. Whenever there is less pressure in the front end than there is outdoors the air from outdoors is going to try to get in the front end. If the front end is tight, the only place air can enter to it while the engine is working steam is through the ash pan, grates, fire, firebox and flues, creating a current of air through the firebox and fire and producing the artificial, or forced draft, of our locomotives.

The draft produced by a blower is somewhat similar to that produced by the exhaust steam. The pipe from the blower extends into the front end to a point directly under the stack, and its end turns up so that when steam passes through it the jet will pass up through the stack. In order to get proper combustion of fuel the draft must be even all through the fire and strong enough to give the proper air supply for the burning. To accomplish this, certain draft appliances are arranged in the front end, and these must be properly adjusted to give best results. The exhaust stand and nozzle must be placed central and in line with the stack, so that the exhaust jet will be properly directed. If the exhaust nozzle is low a petticoat pipe is placed between it and the stack, to keep the exhaust jet from spreading outside of the base of the stack. Sometimes the petticoat pipe is left out and a flare made at the base of the stack, which serves the same purpose.

In

The action of the draft on the fire in most instances is so strong that sparks are carried with the gases and products of combustion into the front end. order that these sparks may be broken up and cooled off before being thrown out of the stack, a deflector plate (sometimes

called a draft sheet or diaphragm) extends outward a few inches from the front flue sheet above the level of the flues, and then turns down at a sharp slope, the bottom edge coming near enough to the bottom of the front end to cause the sparks to be carried well forward. A netting is fitted in the front end to prevent any sparks passing out of the stack unless they first pass through the netting. The mesh of the netting is small enough so that the danger of sparks starting fires is practically done away with.

The majority of roads today use a front end patterned after the Master Mechanic's standard, i. e., one having a deflector and petticoat pipe. With such a front end the draft through the flues is regulated mainly by the position of the deflector plate; the force or intensity of the draft is regulated by the size of the nozzle and the position of the petticoat pipe.

In order to have an even burning fire the draft through the flues should be equal. This even pull through the flues can be gotten by adjusting the movable slide on the bottom of the deflector plate up or down, as the case indicates. If the fire burns too fast near the flue sheet the draft through the bottom flues is too strong and the plate should be raised. If the fire burns too fast near the door the draft through the upper be lowered to equalize the draft through flues is too strong and the plate should

the flues.

The supply of air to the fire is governed by the intensity of the draft.

The exhaust jet must fill the stack near the base, otherwise the draft will be seriously interfered with.

The petticoat pipe is placed so that the opening between the nozzle and the bottom of the pipe is about the same as that between the top of the pipe and the base of the stack.

Speaking generally, if the petticoat pipe is properly placed, an increase in the size of the nozzle reduces the intensity of the draft, and a reduction in the size of the nozzle increases the intensity of the draft.

It must be remembered that a small nozzle increases the back pressure in the cylinders and reduces the power of the engine.

A bridge in the nozzle has a tendency to spread the exhaust jet and fill the stack better, giving a better draft in some cases, especially on an engine having a large stack and a high nozzle. When a bridge is used the opening of the nozzle should