Part 3
Everyone who has made a tour of the Fair buildings at Chicago, brief though it may have been, has probably found one thing worthy of emphatic condemnation, and that is, the system, or perhaps more truthfully speaking, the lack of system, of ventilation. In none of the buildings is this more uncomfortably apparent than in Machinery Hall where, from the nature of the exhibits, the heat during some of the days is trying indeed, certainly sufficient to interfere materially with the pleasure and profit of sightseeing. The vast skylight area, with the sun beating down upon it, transforms the buildings into veritable hot houses with no means of egress for the heated air nor ingress for fresh air from without. The skylights unfortunately are set on a slope with the roof, whereas, had they been set vertically, and hung on vertical pivots, with ropes handy to turn their edges to the sun, a fair degree of comfort might have been secured. As it is, the atmosphere is overheated and confined, and in Machinery Hall, at least, the discomfort is much increased by the heat radiated from the large assemblage of engines and almost endless length of steam piping. One of the queer edicts that went forth from those in authority at the Fair was that all engines and all boiler fronts should be of immaculate white, much to the well-founded disapproval and annoyance of those builders who had taken special pains to make their exhibits attractive in appearance by such means as finely-finished jackets, nickel plated trimmings and the like. White paint has, therefore, been freely used, but scarcely with wholly pleasing results. Any one, in fact, might well have foreseen what this white color craze for engine decoration would bring about. Bright and clean as the white-painted engines certainly looked when everything was new, it took but a short time for the paint to blister more or less and peel off, and for oil and grease to further disfigure it, and give the originally brilliant white a rusty, dirt-streaked aspect. Those of the engines which were left as the builders sent them—and there are a few of them—certainly shine by contrast, and present an effective and businesslike appearance.
Not a few of the engines shown depart from the ordinary, well-known lines of design, and give the impression that they were built specially for exhibition at the fair. A goodly number of makers, however, show simply their standard types, which have been on the market for longer or shorter periods.
Prominent among the special designs of which several illustrations have already been given in the preceding papers, is a 1200 horse-power, double tandem compound engine, built by Messrs.
McIntosh, Seymour & Co., of Auburn, N. Y. The high pressure cylinders of this engine measure eighteen, and the low pressure cylinders, thirty-two inches in diameter, while the stroke amounts to three feet. A speed of 112 revolutions per minute is maintained. The sectional view, which is given of one of the pairs of cylinders, will help to give a better idea of some of the principal details of the design.
/Fig. 3.jpg) |
Between the high and low pressure cylinders there is what the builders call their split connecting head and metallic packing sleeve. This sleeve is lined with compressed Babbitt metal, and is bored out to exactly fit the piston rod, which runs in it. The self-adjusting block, as is shown in the section through the tube, takes up wear, should any occur, from the weight of the rod and pistons. The bearing surface of the piston rod on the packing sleeve is nearly as great as that of the cross-head, and forms a good method of guiding the pistons and supporting their weight, allowing them to be suspended exactly central in the cylinders. The piston rod being steered at two points, that is, the pack1ng tube and the cross-head, at some distance from each other, makes the running of the engine very smooth. The packing sleeve also does away with all stuffing boxes between the two cylinders, and is arranged so that it can be pushed into the high-pressure cylinder by loosening up the packing gland. By removing the distance pieces in the split connecting heads, the low-pressure cylinder heads can thus be slid away from the low-pressure cylinders, and the latter are made easily accessible without disturbing the high-pressure cylinders in any way. All the cylinders are provided with relief valves of special design, which can be set to open automatically at any desired pressure, and at the same time can be opened by hand, serving as cylinder cocks.
The main valves of the engine are of the piston type, with the two ends extended to meet in the centre, so that when one of them is opened on the steam end, the port connects, not with the steam chest, but with the central space in the valve, ports being cut through from this space to the exterior to connect with the steam chest proper. On the outside of the valves in the steam chests ride simple sleeves which serve as auxiliary cut-off valves, and arc directly under the control of the governor, being, thus, automatic in their action. The main valve on each cylinder is driven by a fixed eccentric. The main valve seat consists of a ring, or rather two rings, made in one piece and connected by several bridges across the port-opening which the space between them forms. The seat is crescent shaped, split and adjustable to fit the valve, by the stem which extends to the upper side of the steam chest, where it can be turned by a box wrench. The adjustment can be easily and quickly made.
The governor is very similar to the governor used on the single cylinder engines built by the same firm, except that the eccentric, instead of being moved across the shaft, is simply rotated about it by the action of the governor weights, correspondingly changing the point of cut-off. A plate spring is used in the governor. Both sides of the engine are operated from the same governor through the intervention of a rock-shaft, which extends across and drives the cut-off valves on the further side.
An especially noteworthy feature of these engines is found in the fact that auxiliary shafts are used to carry the governor and eccentrics, and also the transmission gear wheel driving the condenser. These auxiliary shafts are driven by means of drag links which, in turn, receive their motion from extensions of the main crank pins, the object of the whole arrangement having been to reduce the sizes of the different parts of the valve gear and to correspondingly decrease their friction. The governor, in virtue of this feature of the design, also is brought down to a smaller size than usual, and is more sensitive and will act more quickly than 1f it were mounted on the main shaft. The cut-off valves are, to a certain extent, cylindrical grid-iron valves, as will be understood from the sectional view. The high pressure cylinders are provided with steam jackets, and the receivers between the cylinders are filled with copper heating coils, presenting a large amount of heating surface, and tending to give perfectly dry steam at the entrance to the low pressure cylinders. The builders argue that the cause of inefficiency of steam jackets on high pressure cylinders, as ordinarily made, is lack of proper circulation through the jackets, and that a very rapid circulation is necessary to render them operative. By the present arrangement the temperature of the steam in the receiver being much lower than that in the coil, a very considerable amount of condensation takes place in the receiver coil, and as this is fed from the high pressure cylinder jacket only, a brisk circulation is insured in the latter. The pipes from the high-pressure cylinders to the receivers are also fitted with steam separators to catch any water, which may be carried along by the passing steam.
The main shaft of the engine is made of hammered wrought iron, measures fourteen inches in diameter in the main bearings, sixteen inches in diameter between them, and weighs about 33,000 pounds. The main bearings, which are twenty-four inches long, are provided with water jacket shells lined with Babbit metal. The lower one in each case is machined on the outside to the shape of a true sphere, and the bed frames are recessed to correspond. In this way a ball and socket bearing is formed for each journal, insuring uniform distribution of pressure over its surface.
Through bolts, tightened up after the bearings have been allowed to align themselves properly, fasten the latter securely to the frame. The shells are provided with cheek pieces for taking up wear horizontally, and can be slid around and taken out in a few minutes by jacking up the shaft enough to take the weight off the bearings. The lower cross-head guides also are water-jacketed, being cored out for this purpose. They are separate from the frame. Underneath the bearings, and cast in the frame, is a large oil-settling chamber. Bronze rings are placed on the shaft at the end of the journals, which throw all oil fed to the bearings into channels and lead it into this settling chamber, which is provided with a gauge glass showing the amount of oil in it. A small eccentric on the drag link shaft above mentioned drives an oil pump, the suction pipe of which is connected with the oil-settling chamber, while the delivery pipe feeds the oil to the upper sides of the journals. This oiling device appears to be eminently satisfactory in its operation. The oiling, it will be understood, is continuous and automatic, and the bearings are kept practically flooded. The engine frames extend out under and support the high-pressure cylinders, and the latter are bolted to them, but still are free to move longitudinally to compensate for expansion and contraction of the cylinders with varying temperatures. The fly-wheel is not the least interesting part of the engine, being cast in four pieces, with two sets of arms; in fact, it is practically made up of two wheels, placed side by side upon the shaft and bolted together. Each of these four pieces is cast separately, planed up, and bolted together by reamed bolts, the splits in the rim of each half being placed opposite each other. The wheel is prevented from bursting by twenty-four three-inch bolts at the rim, and sixteen two and five-eighth inch bolts at the hub. This, of course, does not include bolts holding the hub and rim together laterally. The rims are provided with broad internal flanges in the centre and at the edge for stiffening the wheel and preventing oil from getting on the belts. The wheel is sixteen feet in diameter, and seventy-eight inches broad, and weighs 62,000 pounds. The total weight 0f the engine is 250,000 pounds.
/Fig. 4.jpg) |
/Fig. 6.jpg) |
The
Ball & Wood Company, of New York, show, altogether, five engines, the exhibit being made up of two of their simple automatic engines, with sixteen by sixteen-inch cylinders, rated at 150 horse-power each; two tandem-compound engines with extended base, cylinders measuring thirteen by twenty by sixteen inches, and also rated at 150 horse-power each; and one cross-compound engine of 200 horse-power, with cylinders measuring fourteen by twenty two by twelve inches. The engines are connected by belts to sixteen Brush dynamos, which furnish current for arc lights used in the Exposition grounds. General and detail views of the cross-compound and of one of the tandem-compound engines are given in this number. A feature of these engines which at once attracts attention is the arrangement of the low-pressure valves. It will be observed that the valve chest on the low-pressure cylinder is cylindrical in shape, and is placed transversely to the axis of the cylinder, and directly underneath it. In the sectional view, small arrows in the passages indicate the direction of the flow of the steam, and larger arrows in the moving parts show the direction of their motion. The valve chest is made very large in diameter, so that the steam ports are short and direct. Two double-ported valves, with arc-shaped faces fitting the bore of the valve chest, are placed opposite each other and are mounted loosely on a central valve stem which drives them both and allows both to be held in contact with their faces by steam pressure. Steam is admitted from the valve chest over the edge on the end of the valve, and also through the port in the valve, thus giving a very rapid and wide opening. At the same time the exhaust from the other end of cylinder, has a very direct passage to the condenser. The valve stem carries on its outer end a rock arm which receives motion from a simple crank pin on the outside of the balance wheel, thus dispensing with an eccentric and having all the parts easily accessible. The whole valve mechanism is made very simple by this arrangement, the number of parts is small, and the valves, as already intimated, give a wide and quick opening and follow up their wear with steam pressure. The clearance also is small owing to the short and direct ports, which, moreover, are so located, as will be understood from the illustration, that they readily drain away water accumulations from the cylinder and reduce the chances of accident from such accumulations.
/Fig. 5.jpg) |
The valve on the high-pressure cylinder is substantially the same as that used in the Ball engine, described in the preceding paper. An additional view of it is given here, together with a view of the inside of the high-pressure valve chest. It may not be amiss to repeat that the valve is made in two parts, with telescopic sleeves connecting them and allowing the valve faces, which are opposite each other, to be held against their respective seats by steam pressure. The steam, it must be remembered, is admitted to the interior of sleeves and thence through the ports into the cylinder, from which it is exhausted past the ends of the valve into the steam chest and out through the exhaust pipe at the bottom. The diameter of the sleeves, of course, determines the amount of pressure with which part of the valve is held to its seat. A judicious choice insures just enough pressure for good contact and not enough to cause undue friction and wear.
/Fig. 7.jpg) |
The main features of the governor of the engine are well shown in the annexed engravings. The hub of the governor wheel is shown with the eccentric A bolted to its outer end, and forming practically part of it. The eccentric strap B is made in halves, and is held in place on the eccentric by a flange on one side and a plate, C', on the other. The governor weights are connected by links, D, to studs in the sides of the eccentric strap, so that the strap and the plate Care turned slightly around the eccentric by the radial movement of the weights. Motion for the valve is taken from the crank pin, E. Since the radial movements of the weights turn the plate C around its centre, which is eccentric to the shaft, the pin E naturally is moved through the arc of a circle whose centre is the centre of the plate. The curved path of the crank pin E is made to give almost a constant lead to the valve until a very early cut-off is reached, when the lead rapidly disappears. It will be seen that only two moving surfaces are interposed between the shaft and the road, which actuates the valve. Of these the crank-pin if is practically the only wearing surface, as it is the only one constantly in motion relatively to the surfaces with which it is in contact. The other, the eccentric strap, moves on the eccentric only when the weights change their position.
/Fig. 8.jpg) |
A further contribution to the high-speed, automatic engine exhibit is made by the
New York Safety Steam Power Company, of New York, one of whose centre-crank engines, slightly different in point of valve detail from the company's standard type, is shown driving some electrical machinery. In this engine, as in the one just described, a relatively small degree of clearance is secured by having the steam ports close to the ends of the cylinder. Unlike the standard type engine, which has only one main valve, the engine on exhibition has two main valves, or, perhaps more correctly speaking, the main valve is made up of two parts, the detail view shown being a longitudinal section through one of them. Each of the parts has its separate valve stem, and the two stems, in turn, are connected and driven by one eccentric rod as shown in the general view.
The valves are of the balanced piston type and are controlled with corresponding ease by the governor. The paths of the live and exhaust steam in getting to and from the cylinder need no special explanation; the sectional view tells its own story.
The main valve stem which works the two valves through the intervention of the two subsidiary stems connected, as already stated, by a crosspiece, passes through an accurately squared cross-head, which slides in a long squared guide, firmly fixed to the engine frame. This cross-head has a steel pin projecting from one side, which takes the eccentric rod; thus but one pin-journal is employed between the valve stem and the eccentric.
In the governor two eccentrics are used. The main eccentric has a slotted arm, which projects radially and is hung upon a pin, or shaft, having a bearing in the governor frame, as shown above. The secondary eccentric shaft, located below, carries two arms, which are connected by links to the levers supporting the governor weights; the other end of the shaft is a small eccentric, which fits into a block which has vertical play between guides affixed to the arm of the main eccentric.
/Fig. 11.jpg) |
The action of the governor is as follows: When the engine is at rest, or is moving at a speed so slow that the tension of the spring overcomes the centrifugal force of the weights, the centre of the main eccentric is at its extreme point distant from the centre of the shaft, and the valve has its greatest travel, the steam being allowed to follow the piston to nearly seven-eighths of the stroke. As the engine increases in speed, and the centrifugal force of the weights overcomes the tension of the spring, the cam is slightly turned to its block, and throws the centre of the main eccentric nearer and nearer to the centre line of the crank, until the desired speed is attained. When the limit of its throw is reached, the travel of the valve is only equal to the lap and lead of the valve. The leverage being great, and the eccentricity of the cam being very slight, but little force is necessary to partly rotate the cam and move the main eccentric.
On the other hand, the resistance of the cam to any opposite force is so great that, when connected, the main eccentric cannot be shifted, except by reason of the movement of the weights and lever connections of the cam shaft. The swinging of the eccentric causes the lead to increase as the travel of the valve shortens. The speed of the engine may be varied either by change in the tension of the one spring employed, or by change in the position of the weights, or both. The direction in which an engine shall run is also within the control of the engineer, and the changes necessary to reverse can be quickly made. The governing mechanism is an independent part of the governor wheel, complete in itself, and can be applied without much trouble to any other wheel, should it become necessary or desirable to make a change in size.
The engine frame is cast in one piece, embracing all the bearings of the engine, and a drip pan extends around the bottom edge to collect oil and water drippings and carry them to a common point of discharge. The engine shown at the Fair has a 15½ x 16-inch cylinder, runs at a speed of 250 revolutions per minute, and is rated at 150 horsepower.
The exhibit of the
Bass Foundry and Machine Works, of Fort Wayne, Ind., consists of one of their regular cross-compound Corliss condensing engines, rated at 300 horsepower. The engine, which is driving dynamos for incandescent lighting, is worked in connection with a Wheeler surface condenser, and has sixteen and thirty inch cylinders, with a stroke of forty-two inches. The driving pulley is sixteen feet in diameter and has a forty-two inch face. The cut-off in both the high and the low-pressure cylinder is under the control of the governor. The engraving, which is given of the engine shows all its principal features quite clearly, and makes a more detailed description unnecessary.
One of the features of the transportation facilities at the Fair is the Intramural Railway, which, as is generally known, is operated electrically. The current for the line is supplied by a gigantic 2,000 horse-power multi-polar railway generator, built by the
General Electric Company, of New York, and driven by a correspondingly imposing cross-compound condensing engine of the Reynolds-Corliss type, made by the
E. P. Allis Company, of Milwaukee, Wis. The engine and generator, while not, strictly speaking, one of the regular exhibits, form an interesting addition to the Machinery Hall display, and reference to them in connection with the present account of the World's Fair steam engines is, therefore, not inappropriate. They are set up in the Intramural Railway powerhouse, and enjoy the distinction of being the largest combination of this kind in the world. The generator itself is a twelve-pole compound wound machine. Each pole is first wound in usual spool fashion and then securely bolted to the massive iron field constructed of two enormous semi-circles of cast-steel, bolted together the lower of which is provided with supporting feet. This field is fifteen feet in diameter, and weighs considerably over 80,000 pounds. The breadth is just three feet. The armature is of the iron clad, ventilating type; that is to say, each of its separate windings is buried in its individual mica-lined slot in the exterior surface of the laminated body. The armature is wound on a cast iron spider weighing over f1fteen tons, which is rigidly keyed to the ponderous shaft of the immense engine. The diameter of the armature is ten and a half feet; its breadth, over three feet, and its weight, over thirty-five tons. The shaft to which it is keyed is two feet in diameter, and weighs fifty-f1ve tons. The commutator is seven feet six inches in diameter. The temperature of the armature, under full load, will not rise over 40 C. above the average temperature of a room.
The brush holders, of which there are twelve sets, corresponding to the twelve poles, are of a novel design. They are carried on an outside brush holder yoke, supported on one side of the field magnet frame, and are moved into position conveniently by means of a special shifting gear, operated by a hand wheel. The brushes are easily accessible from a staircase passing over the revolving shaft. The generator is entirely independent of the engine, with the exception of the armature, which is f1tted to the shaft.
The efficiency of this enormous creation is claimed to be ninety-six per cent. In its mechanical construction special provision was made for allowing a wide fluctuation of load and speed without affecting the efficiency of the machine. The number of revolutions per minute at which it runs is seventy-five. It is wound for 600 volts.
The engine driving this mammoth generator, and to which brief reference has already been made above, has a high-pressure cylinder thirty-two inches in diameter, and a low-pressure cylinder sixty-two inches in diameter, the stroke being sixty inches. Both engine and generator run at a speed of seventy-five revolutions per minute. The weight of shaft and its load is about 160 tons. The fly-wheel is twenty-five feet diameter and weighs eighty-two tons. A thirty-two by sixteen-inch Reynolds vertical air pump and condenser, fitted with a Corliss valve gear, works in connection with the engine, which is specially heavy in design and so arranged that either side is capable of handling 2,000 horsepower in case of necessity.
The exhibit of Messrs.
Russell & Company, of Massillon, Ohio, comprises six automatic engines. One of these is a double tandem-compound, four-valve engine, measuring 15x24x24 inches, and running at a speed of 125 revolutions per minute. It has a balance wheel measuring 120 by 60 inches, and weighing 36,000 pounds, and the total shipping weight of the two engines complete amounts to 89,172 pounds. The engines will develop 600 horsepower, with a claimed water consumption, accounted for by the indicator, of 14½ pounds per horse-power per hour running non-condensing. The admission and cutoff valves are triple-ported, balanced slide valves, balancing being effected by admitting steam between the valve faces, leaving narrow strips or bridges for the valves to ride on. Actual contact of surfaces is prevented, and the valves are really carried between layers of steam, making their movement a very easy one. The cutoff valves slide on the backs of the main valves, and are operated by a separate eccentric, which is connected to the governor so as to cut-off proportionately to the load. The extreme range of cut-off extends from 0 to ¾ stroke. The cut-off eccentric, as usual in governing arrangements of this kind, fits loosely on the engine shaft and is connected with the weight arms in such a manner that it is moved around the engine shaft, either forward or backward, as the weights change their position, thereby cutting the steam off earlier or later in the stroke as the governor, or more properly the weights, adjust themselves to the load. When the cut-off eccentric is rotated forward, that is around the shaft in the direction the engine runs, the steam is cut off earlier in the stroke; when the eccentric is rotated backward the steam is cut-off later in the stroke.
/Fig. 14.jpg) |
The exhaust valves are cylindrical in shape and are operated through wrist-plates by the same eccentric that works the main steam valves, but their connection to the wrist-plates is such as to insure a "dwell" at the time of steam admission, and a correspondingly rapid motion at the time of release. This makes the maximum travel of the exhaust valves occur at a time when the pressure upon them is very small and insures smooth working. The whole valve gear, it will be understood, is designed so that the cut-off valves of both high and low-pressure cylinders are under the control of the governor.
A second compound engine, shown by Messrs.
Russell & Co., is of their single valve type, with 30x20½-x20inch cylinders, and running at a speed of 180 turns per minute. This engine will develop 200 horsepower on a claimed consumption, as accounted for by the indicator, of eighteen pounds of steam per horsepower per hour when running condensing, and twenty-two pounds when running non-condensing. The main features of this engine are well shown in the sectional view of the cylinders and valve chests. In addition to this engine there are two simple, 17 x 24-inch, four-valve automatic engines, running at 150 turns per minute, and essentially the same, so far as valve details are concerned, as the four-valve, double-compound engine already described. Each of these engines will develop 200 horse-power, with claimed water consumption, as in the preceding case, of eighteen and twenty-two pounds per horsepower per hour when running condensing and non-condensing respectively.
/Fig. 15.jpg) |
A fifth engine, exhibited by the same builders, is a simple 13 x 18-inch single valve automatic engine, running at 235 turns per minute and designed for an economic load of 100 horse-power, the water consumption claimed for this engine being twenty-two pounds per horse-power per hour when condensing and twenty-six pounds when non-condensing. The valve of this engine takes steam from underneath and is held to its seat by enough steam being admitted into the chest to accomplish this purpose without overloading it. The steam is admitted to the cylinders through "carry-over" double ports, and the exhaust is accomplished through a "D" passage.
Part 4
An interesting and most valuable outcome of the steam engine exhibit at the Fair will probably be found in the results of the series of tests which it has been proposed to make in connection with a number of the engines. Among these will be, to begin with, the quadruple expansion Allis engine referred to in the first of these papers. This engine represents probably the most advanced design in the steam engine line and, as pointed out by the sub-committee of jurors having the proposed trials in hand, no public determination of the possibilities of such an engine as to economy has been made up to the present time. It will, therefore, be eminently consistent with the educational interest of the Exposition that a careful and thorough investigation of its performance be instituted. The next engine to be considered in the trials would be that built by Messrs.
Fraser & Chalmers of Chicago, and described further on, the engine being a representative example of a modern, triple-expansion engine of the Corliss slow-speed type. The Buckeye triple expansion engine, described in the May number of this magazine, would also be tested as an example of a two-valve engine with a shaft governor. Further, the German engine exhibited by
E. Schichau, also previously described, and belonging to the vertical, triple-expansion type, would be tried as an example of foreign, continental practice, while the
Galloways compound engine would be taken as a representative English design. A vertical Allis engine, remaining to be described, would follow in the list, embodying a novel principle calculated to give economy under variable loads. This principle lies in the valve gear, which is operated so as to preserve a f1xed initial pressure and cutoff, whatever the amount of load. Whenever the load is less than that corresponding to this cut-off, the resulting increase of speed causes the governor to shut off altogether the supply of steam, and, as in some gas engines, no further admission occurs until a reduction of the speed below the normal causes the governor again to open the admission valve. The novelty of this principle is thought sufficient to warrant a test, and it would be made in a series covering several loads. Next would come the Westinghouse steeple- compound, double-acting engine, illustrated and described in this number, one of the features of which consists in the use of a large clearance volume in the high pressure cylinder, so as to restrict the range of pressure and temperature during expansion. Tests would also be made of the 500 horse-power Ball compound engine, as representative of one class of high-speed, automatic engine of the common type; of a Willans vertical compound engine of English make; and of a number of others not yet particularly specified.
/Fig. 17.jpg) |
Of the
Fraser & Chalmers engine, referred to in this list, a general view is given on the opposite page. The engine, which is rated at 1,000 horse-power and runs at a speed of 64 revolutions per minute, is of the four-cylinder, triple expansion design, having one high-pressure cylinder, 20 inches in diameter; one intermediate cylinder, 34 inches in diameter; and two low-pressure cylinders, each 34 inches in diameter, the stroke of all being 60 inches. The purpose of this arrangement of cylinders is, of course, to equalize the turning moment and the strains and power exerted on each crank as far as possible. All the cylinders are steam jacketed on the heads as well as on the sides. The valve gear is of the regular
Fraser & Chalmers Corliss type. The cut-off gear of the high-pressure cylinder is always under control of the governor, but the novelty appears in the cut-off gears of the remaining cylinders.
If there are no sudden changes of load, the cut-off should be constant in the other cylinders in order to secure a uniform, minimum drop of power between these cylinders, the cut-oft depending upon the size of the receiver and cylinders; but if the load were suddenly and largely reduced there might remain steam enough in the receivers to cause the engine to speed up or run away even if all the steam were cut off from the high-pressure cylinder. On the other hand also, with the sudden imposition of a great increase of load the increased admission of steam in the high-pressure cylinder might not be sufficient to maintain the speed of the engine. To guard against these contingencies the cut-offs of the intermediate and low-pressure cylinders are connected with the governors by means of oil cataracts. A slow motion of the governor will not affect the intermediate or low-pressure cylinders, the cut-off cams being held in position by springs; but any sudden motion of the governor transfers itself instantly to the cut-off cams, which, after this influence has passed, again slowly recede to their normal position. In short, the cut-offs of the intermediate and low-pressure cylinders are changed only in cases of emergency, and not long enough to reduce the economy of the engine. The connecting pieces between the cylinders are made in halves so that they may be taken apart for convenience in examining cylinders and pistons. The engine is of course used condensing, but the condenser in this case is not of the
Fraser & Chalmers design, but one furnished by the
Conover Manufacturing Company of New York, for exhibition in connection with this engine.
One of the most attractive and novel engines on exhibition is the "Dick & Church" four-cylinder triple-expansion engine of the double tandem, cross-compound type, built by the
Phœnix Iron Works Company, of Meadville, Pa. This engine is substantially a combination of two of their tandem-compound engines, illustrated in the May number of this magazine, and the description, which was there given applies largely to the general features of each side of the present design, with the exception that on one side the intermediate cylinder is substituted for the high-pressure cylinder of the regular tandem engine, being secured to the small, or high-pressure bed. The two low-pressure cylinders are placed in the rear, each being carried on a sub-bed. Each side of the engine has substantially the same valve gear as the regular tandem compound engine, and the governor is also substantially the same. This valve gear is placed on the inside. The governor is made double and is placed in the intermediate wheel. It is so cross-connected that the two sides of the engine are compelled to act together, the one governor controlling the valves of all four cylinders, thus insuring close regulation and the proper distribution of load, temperatures and initial thrusts throughout the whole range from friction load to full load. The steam passes from the high-pressure cylinder to the intermediate cylinder on the opposite side, and from this cylinder it is carried by a branched pipe to both of the low- pressure cylinders. These intermediate pipes are connected with the under side of each steam chest, and are kept as high as practicable to prevent the formation of dangerous water traps between cylinders. A neat platform, with steps at the rear, is placed between the engines and over the intermediate pipes. This gives ready and convenient access to the valve gear, cross-head and guides, throttle valve and other parts, and two oil cups, one on each front corner post of the platform railing with pipes leading to all the parts requiring lubrication, including the eccentrics and the pins and bearings of the governor, enable the engineer to keep all working parts thoroughly lubricated while the engine is in motion. The observer cannot fail to note that the cross-connected intermediate pipes, which in most cross-connected engines are such a disfigurement, as well as an obstruction, are entirely hidden by the platform. The cylinders, steam chests, cylinder heads and intermediate pipes have non-conducting coverings, with metal outside lagging. The two sides of the engine are placed close together, but at the same time ample space is provided for all the parts and easy access to all of them. That the engine is compactly built is evident from the fact that, although rated at 525 horse-power, with a maximum capacity of 750 horse-power, it only occupies a floor space of 17 feet 8 inches in width, by 27 feet 7 inches in length, measured clear of the wheels. The high-pressure cylinder is 15 inches in diameter; the intermediate, 24 inches, and the two low-pressure cylinders each measure 26 inches, while the stroke of all is 18 inches. The wheels are 108 inches in diameter, the two outside ones having 26-inch faces, while the centre one has a 38-inch face. The working speed is 200 revolutions per minute. The engine presents a graceful appearance, at the same time impressing the observer with a sense of its massiveness and the great amount of power stored in such compact space, coupled with extreme simplicity of construction.
/Fig. 20.jpg) |
/Fig. 22.jpg) |
Two engines are exhibited by the
Atlas Engine Works of Indianapolis, Ind., one of them representing a single and the other a double, tandem-com pound design. The cylinder dimensions are the same in each, 14x24 inches, with 30-inch strokes. Both engines are designed to run at 150 revolutions per minute, the single tandem-compound engine driving ten 50-light Thomson-Houston dynamos, while the double engine is connected to one of the large Westinghouse, 10,000-light incandescent dynamos, their rating being 500 and 1000 horse-power respectively. With the exception of the high-pressure cylinders, these engines are samples of the single valve automatic heavy-duty engine, which the makers have been building for several years. This engine has several notable features, among which are the massive bed-plate, the main bearing, with removable boxes, the peculiar form of cross-heads and the automatic dead wheel governor. This governor, like those of other builders, controls the engine by changing the throw and angular advance of the eccentric, but is so arranged that the action of the weights and springs is reinforced by the inertia of a heavy loose wheel, which gives it unusual power. The valve is a flat slide perforated by steam and exhaust ports, and relieved from pressure by a massive pressure plate. To meet the demand for engines of higher efficiency, the builders have compounded these engines, by adding high-pressure cylinders. These are of the four-valve type, there being separate steam and exhaust valves for each end. The cylinders are supported by feet on the foundations at the back of the single valve cylinders, which serve as the low-pressure cylinders. The high and low-pressure cylinders are connected by a distance piece so designed as to permit the removal of both cylinder heads and pistons without disturbing the connection.
/Fig. 23.jpg) |
The striking feature about the high-pressure cylinders is found in the valve gear, which is of a novel and unusual kind. The rather high speed at which the engines were designed to run, of course, precluded the use of the regular Corliss, or any form of releasing valve gear. The designer was, therefore, compelled to devise a positive motion which would accomplish the same results and be unaffected by the speed. This he has succeeded in doing in a very simple and effective manner. The valves are of a form for which the builders obtained a patent several years ago. They are like the Corliss, except that, like the seats, they are provided with a number of ports. This gives them the property of the well-known gridiron valve. The valve seats are sleeves or bushings forced into bored holes in the cylinder, and are removable when worn or injured. The ports are cut in the valves and seats by an index-milling machine, so that perfect correspondence is secured. At the same time, on the outer ends of the valve and seat, the ports are marked with the cutter, which affords a convenient and accurate means of ascertaining the set of the valves when the covering bonnet is removed. The valves have stems and supporting bonnets like in the Corliss arrangement, but instead of the usual catch blocks on the valve stem cranks, the crank pins carry steel cam rollers, about 2¼ inches in diameter by 1½-inch face, on anti-friction roller bearings. Instead of the Corliss wrist plate, there is a sliding piece supported by brackets on the cylinder between the valve bonnets. The stem of the low-pressure valve is prolonged through a stuffing box at the back of the steam chest and connects by means of a drop latch with a wrist on the sliding piece. This gives the sliding piece, when the engine is running, a reciprocating motion variable in extent with the throw of the eccentric of the shaft governor. On the sliding piece is mounted a set of cams which engage the rollers of the valve cranks and operate the valves. The cams are fastened to the sliding piece by bolts passing through slotted holes, which permit their adjustment. The steam valve cams are made in two parts so placed with reference to each other as to form a groove embracing the roller on the valve crank. This groove has two level portions joined by an incline.
/Fig. 25.jpg) |
Into the ends of the two parts of the cam are screwed studs connecting them by a yoke, the stem of which passes through a lug on the sliding piece. The nuts on the studs permit adjustment of the two parts of the cam to take up lost motion, and the nuts on the yoke stem provide for adjusting the whole cam when setting the valves. The motion of the cam slide is such that at the end of a stroke of the piston, the cam roller is just at the top of the incline of the cam groove. While the engine is passing the centre, the cam slide moves far enough to carry the roller down the incline and to open the valve. When cutting off at the shortest point, the cam slide moves only far enough to give the valve its full opening, and the eccentric, passing its centre, reverses the motion of the slide and immediately closes the valve. When the load requires a longer admission of steam, the governor increases the throw of the eccentric and the cam roll passes beyond the incline of the cam and runs upon the lower level, holding the valve wide open until, by the return motion of the slide, the incline is again reached, which shuts the valve and cuts off the steam. The roller then runs upon the upper level, holding the valve shut until the end of the return piston. The exhaust valve cranks are double-armed, one arm of each carrying a cam roller and the other two being connected by a parallel rod, which compels the pair of valves to move together. The opening of one valve shuts the other. The length of the parallel rod may be adjusted by means of right and left threads at the ends, so that the lap of each valve is greatest on the closing side. The effect of this is to close one valve just before the other opens, and the compression and release may by this means be made to occur at the desired points. The exhaust cams consist of a single piece each, acting on the upper side of the valve crank roller. Each cam opens the valve at its own end of the cylinder and closes the one at the other end. The effect of this arrangement is that while the point of closure of the steam valves varies as determined by the governor, the exhaust valves, though operated by the same eccentric, have a uniform motion, opening and closing at the end of each piston stroke. Indicator cards taken from one of these engines show the distribution of steam to be nearly perfect. By means of the drop-latch the cam slide may be disconnected from the eccentric, and a starting bar is provided by means of which the valves may be worked by hand to back the engine off the centre in starting. The whole arrangement is neat in appearance and noiseless in action.
/Fig. 24.jpg) |
While the
Westinghouse Machine Company of Pittsburgh have at the Fair a number of their well-known "Junior," "Standard" and regular compound engines, the chief interest of their exhibit lies in six steeple-compound engines of an entirely new type recently developed by them, the engines being double and not single-acting like the other Westinghouse engines, and each being rated at 1ooo horse-power, which is the smallest size of this type to be turned out. The general and sectional views and the end elevation of one of these engines, which accompany this paper, clearly explain the main features of the design. The low-pressure cylinder is mounted above the high-pressure cylinder and has a flat slide valve. The high-pressure valve, on the other hand, is of the piston type, and the exhaust from the lower end of the high-pressure cylinder passes up through the inside of the valve on its way to the upper cylinder. In order to afford adequate cushioning for a valve so large and heavy as this one, the designer provided a special cylinder for the purpose, shown at the right of and below the high-pressure valve chest in the vertical section. The high-pressure eccentric, it will be noticed, is mounted on the outside of the crank case, next to the governor wheel, as in the regular Westinghouse compound engines, the motion being transmitted to the valve rod proper through several rocker arms and a connection with the cushioning cylinder plunger in the manner shown. The cushioning medium in this cylinder may be either air or steam, and when steam connections are made to the cylinder, it may be used as a starting cylinder for the high-pressure valve, connection of the latter with its eccentric being temporarily broken by a special disengaging gear provided for the purpose.
/Fig. 26.jpg) |
/Fig. 27.jpg) |
The low-pressure eccentric which, unlike the automatically governed high-pressure one, provides for a fixed cutoff, is mounted inside of the crank case and connects with a cross head from which two rods lead off to the low-pressure valve, straddling that on the high-pressure cylinder. The engines are all direct-connected to Westinghouse electric generators, and run at a speed of 200 revolutions per minute. The high and low-pressure cylinders measure respectively twenty-two and one-half and thirty-seven inches in diameter, and have a stroke of twenty-two inches.
Information Sources
- Part 1,Cassier's Magazine, by George L. Clark, May 1893 pgs. 215-232
- Part 2,Cassier's Magazine, by George L. Clark, Jun 1893 pgs. 333-344