CHAPTER IV

Engineering conditions in 1860. I meet Mr. Allen. Mr. Allen’s inventions. Analysis of the Allen link.

Before resuming my narrative, it seems desirable to present a brief sketch of steam engineering conditions forty years ago.

The science of thermodynamics had been established on the foundation laid in the experiments of Joule, determining with precision the rate at which, through the medium of water, heat is converted into dynamical force. This science was, however, as yet without practical results. The condensation of steam in the cylinder from the conversion of its heat into mechanical energy was unregarded. The same was true also respecting the far greater loss from the changing temperatures of the surfaces with which the steam comes in contact in alternately entering and leaving the cylinder. The action of these surfaces in transmitting heat from the entering to the exhaust steam without its doing any work was imagined by very few.

In the United States economy of steam was sought only by mechanical means—by cutting off the admission of the steam at an early point of the stroke in a single cylinder and permitting the confined steam to complete the stroke by its expansion. By this means a large saving of steam over that consumed in earlier practice was effected, and with this gain the universal disposition was to rest content.

America was eminently the land of the cut-off system, an early application of which was on steamboats. The earliest device for this purpose was the elegant Stevens cut-off, which still keeps its position on the class of boats to which it was first applied, though commonly modified by the Sickles improvement. In thissystem the exhaust and the admission valves are operated by separate eccentrics on opposite sides of the engine, and all the valves have the amount and rapidity of their opening and closing movements increased by the intervention of wiper cams, those for the admission valves being very long and giving a correspondingly greater enlargement of opening. The valves were double poppet valves, moving nearly in equilibrium in directions vertical to their seats. This cut-off was found to be capable of improvement in one important respect. The closing motion of the valve grew slower as the valve approached its seat, and while the piston was moving most rapidly much steam passed through the ports at a lower pressure, and so a great part of its expansive value was lost. This was technically termed “wire-drawing.” To remedy this defect Mr. Sickels invented his celebrated trip cut-off. The valve, lifted by the Stevens wiper, was liberated by tripping the mechanism, and fell quickly to its seat, which it was prevented from striking forcibly, being caught by water in a dash-pot. The steam was thus cut off sharply and the economy was much improved. The pressure used in this system was only about 25 pounds, the vacuum being relied upon for the larger portion of the power.

On the Great Lakes a pressure of 60 pounds was commonly employed, and the valves were the four cylindrical rotating slide valves afterwards adopted by Mr. Corliss. What was called the cut-off was made by a separate valve located in the steam-pipe somewhere between the engine and the boiler.

On the Mississippi and its tributaries, much higher pressures were carried, condensers were not used, and the admission and release of the steam were generally effected by four single poppet valves, lifted by cams against the pressure of the steam.

On land engines Mr. Sickels’ invention of the trip cut-off stimulated inventors to a multitude of devices for working steam expansively. Of these the one of enduring excellence proved to be that of Mr. Corliss. He applied the trip cut-off to the rotating slide valve, and arrested the motion of the liberated valve by an air-cushion. This proved a satisfactory method, as the valve, moving in directions parallel to its seat, did not need to be stopped at a determinate point. Mr. Corliss applied the governor to varythe point of liberation of the valve, and so produced a variable cut-off, which effected a large saving of steam and regulated the motion of the engine more closely than could be done by a throttle valve outside the steam-chest. This was by far the most prominent of the numerous forms of automatic variable cut-offs, to all of which it was supposed that the liberating feature was essential.

In England, when the steam was worked expansively, it was cut off by a separately driven valve on the back of the main slide valve, the point of cut-off being fixed; and the regulation was effected by means of the throttle. This system was also largely employed in this country.

The compound engine was unknown in the United States. I once saw at some place in New York City, now forgotten, a Wolff engine—a small beam-engine, which had been imported from England. It was visited as a curiosity by several engineers, and I remember Mr. Horatio Allen, then president of the Novelty Iron Works, remarking, “It is only a cut-off.”

In the south of England the Wolff system was used to a limited extent. I was much interested in the McNaught system, devised, I think, by the same Scotchman who first applied a rotating paper drum to the Watt indicator. The cotton and woolen mills, as their business grew, felt the need of additional power, but dared not employ higher steam pressures in their cylinders, because the beam centers of their engines would not stand the additional stress. McNaught provided an additional cylinder to carry a higher pressure, and applied this pressure directly to the connecting-rod end of the beam. The exhaust from this cylinder was taken into the old cylinder at the old pressure. This latter cylinder then exerted the same power it always had done. The stresses on the beam centers were not increased, but the power of the engine was doubled, and only a little more steam was used than before. This method of compounding was known as McNaughting, and became common in the manufacturing districts of England and Scotland.

There was one feature which was common to all engines in America and Europe, both ashore and afloat, and of whatever make or name, except locomotives. That was the piston speed, which varied only from 200 to 300 feet per minute. This last wasthe maximum speed, to which every new engine, however novel in other respects, was made to conform.

I come now to the turning-point in my career, and the reflection forces itself upon me, how often in the course of my life incidents trivial in themselves have proved afterwards to have been big with consequences; and how events, sometimes chains of events, beyond my control, of which indeed I had no knowledge, have determined my course. The same must be the case in the lives of many persons, and the thoughtful mind cannot look back on them without being impressed by the mysterious interrelations of our being.

One morning in the winter of 1860-61, Mr. Henry A. Hurlbut, of the firm of Swift, Hurlbut & Co., wholesale dealers in hats at No. 65 Broadway, and who was interested in my governor manufacture, called upon me to tell me that a friend of his, Mr. Henry A. Burr, manufacturer of felt hat bodies at the corner of Frankfort and Cliff streets in New York, had been having trouble with his engine. He thought my governor was just what he needed, and asked me to accompany him to Mr. Burr’s office, where he would give me the advantage of his personal introduction. In the interview with Mr. Burr which followed, I did not have an opportunity to say a word. After Mr. Hurlbut had explained the object of our visit, Mr. Burr replied that he had had a great deal of trouble with the regulation of his engine, and had thought seriously of getting a Corliss engine in the place of it; but two or three weeks before the builders of the engine had sent him a very skillful engineer, and since he came there had been no further trouble, so he should not need my governor. He invited us to see his engine, in which—since it had been taught to behave itself—he evidently took much pride. We found a pair of beam-engines of 5 feet stroke, running at 25 revolutions per minute, made by Thurston & Gardiner of Providence. They had the usual poppet valves and the Sickels cut-off. This was made adjustable, and was regulated by the governor. At the time of our entrance, Mr. Allen, the new engineer, was engaged on the scaffold. Mr. Burr called him and he came down, and at Mr. Burr’s request explained to us the variable liberating mechanism and what he had done to make it work satisfactorily. The regulation did not appearto me to be very close, and I made a determined effort to induce Mr. Burr to substitute one of my governors. I showed him a cut of the governor, and pointed out its combination of power and sensitiveness, but all in vain. He was satisfied with things as they were, and I went away crestfallen, having lost not only the sale of a governor, but also an opportunity for a triumph in a very important place. But I did not know to whom I had in fact been talking.

As we were leaving, Mr. Allen asked me if I would call some time and see him—he had something he thought I would be interested in. I called soon after. He told me he had a plan for a variable cut-off with positive movements, which he thought would avoid defects in the liberating gear. He had had it in his mind a good while, but did not think it could be used, because the governor could not handle the block in his link so as to maintain uniform motion, and he had been inclined to abandon the idea; but when he heard me describing my governor to Mr. Burr, it occurred to him that that governor would do it, and he would like to explain his plan to me. He had no drawing, not a line; the design existed only in his mind. He put down his ideas, as he fitly expressed it, with chalk on the engine-room floor, and that rude sketch represented the perfect system.

When his plan came to be analyzed, it was found that everything had been thought out and provided for, with a single exception afterwards provided by Mr. Allen, as will be described. But the wonder did not stop there. Mr. Allen had remedied the defect in the link motion of making a narrow opening for admission when cutting off early, by employing a four-opening admission valve of unique design at each end of the cylinder, and also by greatly enlarging the opening movements.

The four-opening valve required four seats in one plane, and it was important that these should be as narrow as possible. For this purpose Mr. Allen employed the Corliss wrist-plate movement to reduce the lap of the valve, and, by an elegant improvement on this movement, he made it available also to enlarge the openings. This improvement consisted in the employment of two rockers having a common axis and separate driving-arms, as well as driven arms, for each valve. The driving-arms were made tovibrate a long way towards their dead points, and the increased opening movement in arc thus obtained was imparted directly to the valve. This combination of an enlarged opening with a reduced lap was perhaps the most surprising feature of Mr. Allen’s system.

The four-opening equilibrium valve, afterwards invented by Mr. Allen and since 1876 always employed, requires but two seats in one plane. These could therefore be made wider. The division of the driving-arm was then dispensed with, and the enlarged openings were obtained by increasing the length of the driven arms.

That this remarkable system of ports and movements should have been elaborated in the mind of a man who had no knowledge of mechanics except what he had absorbed in engine-rooms must stand among the marvels of inventive power.

The accompanying diagram represents the lines put down by Mr. Allen on his engine-room floor and since retained, except that it is now adapted to the more simple movement, with a single driving-arm on the rocker, as previously described.

The eccentric is formed on the shaft coincident with the crank of the engine, so that the two arrive at their dead points simultaneously.

The angular vibration of the line connecting the center of the eccentric with the trunnions of the link is the same as that of the connecting-rod.

The connecting-rod of the length always used by me, namely, six cranks, makes the piston velocity at the head end of the cylinder 40 per cent. greater than at the crank end. By this construction the valve velocities were made to vary in the same ratio.

A connecting-rod five cranks in length would increase this difference in piston velocities to 50 per cent., and one four cranks in length would increase it to 66 per cent.

After Mr. Allen had explained his plan to me, I expressed my confidence that my governor would meet its requirements, and observed that it would enable a variable cut-off engine to be run as fast as a locomotive. Somewhat to my surprise, he replied that he wanted his cut-off compared with the liberating cut-off turn for turn; that it had an advantage which he thought would cause it to be generally preferred at the same speed.

RELEASE AND COMPRESSION¹⁵⁄₁₆ OF THE STROKEPORTER-ALLEN ENGINE.DIAGRAM OF ADMISSION-VALVE MOVEMENTS.TO VALVE ATCRANK ENDMEAN POSITION OF ROD¹⁄₂ CUT OFF³⁄₈ CUT OFF¹⁄₄ CUT OFF¹⁄₈ CUT OFF¹⁄₂ CUT OFF³⁄₈ CUT OFF¹⁄₄ CUT OFF¹⁄₈ CUT OFFRADIUS OF LINKTO VALVE ATHEAD ENDA. POINTS OF ADMISSION AND CUT-OFF.FOR DISTINCTNESS OF REPRESENTATION, THE THROWOF THE ECCENTRIC IS SHOWN ¹⁄₄ THAT OF THE CRANK.IN PRACTICE IT IS ONLY ¹⁄₁₂ THAT OF THE CRANK.The Diagram Drawn by Mr. Allen on his Engine-room Floor.

The Diagram Drawn by Mr. Allen on his Engine-room Floor.

John F. Allen

I was then ignorant of his state of mind on that subject, or of what had produced it. I learned these afterwards, and will state them here. In one of our interviews, in reply to my question as to what had led him to make this invention, he told me it was his experience when he was engineer of the propeller “Curlew,” a freight-boat running on Long Island Sound, between New York and Providence, which had a Corliss engine. He became impressed with what he thought to be a serious defect in the liberating system. The governor did not control the point of cut-off, but the point of release; this point being at the beginning of the closing movement of the valve, while the cut-off took place near the end of that movement. When the engine was worked up to nearly its capacity, as was the case in a ship, the port was opened wide, and quite an appreciable time elapsed between the release and the cut-off. During this interval the piston advanced considerably, and if the engine ran fast enough it might get to the very end of the stroke before the cut-off took place. He said that in smooth water they had no trouble, but in the open ocean, going around Point Judith, it was always rough, and sometimes in stormy weather the screw would be thrown quite out of the water, and the engine, having no fly-wheel, would race most furiously. The faster it ran the further the steam would follow, and was pumped out of the boiler very rapidly. Springs were employed to accelerate the closing movement of the valves, but in these cases they seemed to be of little use, and were continually breaking. He saw that this difficulty could be avoided only by a positive motion gear which would enable the governor to control the point of cut-off itself; and, accordingly, he set himself to work to devise such a system. We know now that this judgment, formed from observations made under very exceptional conditions, was not well founded. The difficulty in question does not practically exist in engines having fly-wheels and the present improved liberating gear, and running at moderate speeds; but the experience naturally made a deep impression upon Mr. Allen’s mind, and led to the invention of the positive motion system.

This he did not tell me at the time, so that I was at a loss to understand his reluctance to admit what was really the great value of his invention. However, I told him I would be willing to attempt its introduction, provided he would allow me to apply it at once to a high-speed engine; that being a field into which the liberating system could not enter. We had quite an argument on this point. I told him his invention interested me only because it would enable two or three times the power to be obtained from a given engine without additional stress on any part, the fly-wheel to be reduced in size, and the means for getting up the speed of machinery to be largely dispensed with. I represented to him also that a high-speed engine ought to be more economical and to give a more nearly uniform motion.

He finally agreed to my condition, and I took him directly to the office of Mr. Richards and engaged him to make an analysis and drawing of Mr. Allen’s system under his direction, and soon afterwards gave him an order for the plans for an experimental engine, 6×15 inches, to make 160 revolutions per minute.

As the diagram of the link motion was at first drawn, the center of the trunnions vibrated in an arc which terminated at pointsonthe line connecting the center of the engine shaft with the ends of the rocker arms, and which in thediagramon page 48 is named “radius of link.”

I determined to work out this link motion myself on a large scale. For this purpose I drew a diagram in which the throw of the eccentric was 4 inches, and the distance from the center of the shaft to that of the trunnions of the link in their mid-position was 12 inches. I made a three-point beam compass. Two of these points were secured permanently on the beam, 12 inches apart. As one of these points traversed the path of the center of the eccentric, the other could be made to traverse the arc of vibration of the trunnions of the link.

I divided the former into 40 equal divisions measured from its dead points, making needle-holes in the circle, in which the taper compass-points would center themselves accurately. The paper was firm and the points of division were fixed with extreme care; and they lasted through all my experiments. I then set out 20 corresponding divisions in the arc of vibration of the centerof the trunnions. These showed distinctly the modification of the motion at the opposite ends of this vibration as already described.

The third point was adjustable on a hinged beam which could be secured in any position. I drew two arcs representing the lead lines of the link, or the lines on which the link would stand when the eccentric was on its dead points. The third point was now secured on its beam at any point on one of the lead lines, when the other points stood, one on the dead point of the eccentric and the other at the end of the trunnion vibration.

The apparatus was now ready for use, the corresponding points on the circle and the arc being numbered alike. By setting the first two points in any corresponding holes, the third point would show the corresponding position of that point of the link at which it was set. I thus set out the movements of six different points of the link, the highest being 12 inches above the trunnions. These represented the movements of the valves of the engine when the block was at these points in the link. The apparatus being firm, it worked with entire precision. To my surprise, it showed much the larger valve opening at the crank end of the cylinder, where the movement of the piston was slowest. That would not do; we wanted just the reverse.

I called Mr. Allen in and showed him the defect. After considering it a few minutes, he said he thought it would be corrected by lowering the trunnions, so that their arc of vibration would coincide with the line of centers at its middle point, instead of terminating on it. This was done, and the result was most successful. The lead was now earlier and the opening wider at the back end of the cylinder, as the greater velocity of the piston at that point required, and the cut-offs on the opposite strokes more equal. The link has always been set in this way, as shown in thediagram.

From this description of the link motion, it will be seen that the correct vertical adjustment of the trunnions of the link was an important matter. To enable this adjustment to be made with precision, and to be corrected, if from wear of the shaft-bearings or other cause this became necessary, I secured the pin on which these trunnions were pivoted to the side of the engine bed in the manner shown in the followingfigure. To hold the wedge securely, the surface of the bed below was reduced, so that the wedge wasseized by the flange. The correct position of this pin was determined by the motions given to the valves.

VERTICAL ADJUSTMENTOF SUSTAINING PINFOR TRUNNIONSOF THE ALLEN LINK

I now took a more prominent part myself in steam-engine design. I had got an idea from Mr. Sparks that took full possession of my mind. This was the exceedingly unmechanical nature of the single or overhanging crank. The engines of the “New York,” built by Caird & Co., of Greenock, were among the first of the direct inverted-cylinder engines applied to screw propulsion. They were then known as the steam-hammer engines, their leading feature being taken from Mr. Nasmyth’s invention. I am not sure but Caird & Co. were the first to make this application. The forward engine had a single crank. The vital defect of this construction became especially apparent in these vertical engines of large power. The stress on the cap bolts during the upward strokes and the deflection of the shaft alternately in opposite directions over the pillow-block as a fulcrum were very serious. Mr. Sparks told me that on his very first voyage he had a great deal of trouble with this forward bearing, and it caused him continual anxiety. He got into such a state of worry and apprehension that as soon as he reached New York he wrote to the firm: “For God’s sake, never make another pair of engines without giving a double crank to the forward engine.” The reply he got was, to mind his own business: they employed him to run their engines; they would attend to the designing of them. He told me not long after that he had the satisfaction of seeing every ship they built except his own disabled,either by a broken shaft or broken pillow-block bolts. He attributed the escape of the “New York” from a like disaster to his own extreme care. They did, however, adopt his suggestion on all future vessels, and, moreover, added a forward crank and pillow-block to the engines already built. This they evidently found themselves compelled to do. I saw this addition afterwards on the “Bremen,” sister ship to the “New York.” The added pillow-block was supported by a heavy casting bolted to the forward end of the bedplate.

I went everywhere visiting engines at work and in process of construction, to observe this particular feature of the overhanging crank, which was universal in horizontal engines. In this class of engines, running slowly, its defective nature was not productive of serious consequences, because no stress was exerted on the cap bolts and the shaft was made larger in proportion to the power of the engine, as it had to carry the fly-wheel. But I was astonished to see the extent to which the overhang of the single crank was allowed. Builders seemed to be perfectly regardless of its unmechanical nature. First, the crank-pin was made with a length of bearing surface equal to about twice its diameter; then a stout collar was formed on the pin between its bearing surface and the crank. The latter was made thick and a long hub was formed on the back of it. I was told that the long hub was necessary in order to give a proper depth of eye to receive the shaft. This being turned down smaller than the journal, so that the crank might be forced on up to a shoulder, the eye needed to be deep or the crank would not be held securely. Finally, the journal boxes were made with flanges on the ends, sometimes projecting a couple of inches. Altogether, the transverse distance from the center line of the engine to the solid support of the shaft in the pillow-block was about twice what it needed to be. I also saw in some cases the eccentric placed between the crank and the pillow-block. Fifteen years later I saw a large engine sent from Belgium to our 1876 Exhibition which was made in this manner.

I determined at once that such a construction would not do for high-speed engines, and proceeded to change every one of these features. The single crank could not be avoided, but its overhang could be much reduced.

OLD AND NEW CRANKSAND JOURNAL BOXES.THE CRANKS ARE SHOWN INTHE VERTICAL POSITION.CRANKS AND TOP AND BOTTOMBOXES ARE SHOWN IN SECTION.

OLD AND NEW CRANKSAND JOURNAL BOXES.

THE CRANKS ARE SHOWN INTHE VERTICAL POSITION.

CRANKS AND TOP AND BOTTOMBOXES ARE SHOWN IN SECTION.

The followingsketchesshow the changes which were then made, and all of which have been retained. The inside collar on the crank-pin was dispensed with and the diameter of the pin was made greater than its length, the projected area beinggenerally increased. The shank of the pin was made larger and shorter, and was riveted at the back. Instead of turning the shaft down smaller than the journal to receive the crank, I made it with a large head for this purpose. The keyway could then be planed out and the key fitted above the surface of the journal, and the joint was so much further from the axis that but little more than one half the depth was required in the crank-eye.

Mr. Corliss had already discarded the flanged boxes. He also first made this bearing in four parts. The wear in the horizontal direction, the direction of the thrust, could then be taken up. For this purpose he used two bolts behind the front side box only. I modified his construction by making the side boxes wider and taking up their wear by wedges behind both of them, thus preserving the alignment. One wedge could also be placed close to the crank. The dotted lines show the width of the side boxes and the location of the wedges. The shaft was made with a collar to hold the bearings in place, and was enlarged in its body. The substitution in place of the crank of the entire disk carrying a counterweight completed these changes. This was the fruit of my first lesson in high-speed engine designing, which had unconsciously been given to me by Mr. Sparks. The oil passage in the pin was added later, as will be described.

I had another piece of good luck. I happened one day to see in the Novelty Iron Works the hubs being bored for the paddle-wheels of the new ship for the Collins line—the “Adriatic.” These were perhaps the largest castings ever made for such a purpose. I observed that they were bored out only half-way around. The opposite side of the hole had been cored to about half an inch greater radius, and three key-seats were cored in it, which needed only to be finished in the key-seating machine. The idea struck me that this would be an excellent way to bore fly-wheels and pulleys. As commonly bored, so that they could be put on the shaft comfortably they were bored too large, their contact with the shaft could then be only on a line opposite the key, and the periphery could not run perfectly true.

I adopted the plan of first boring to the exact size of the shaft and then shifting the piece about an eighth of an inch, and boring out a slender crescent, the opposite points of which extended alittle more than half-way around. The keyway was cut in the middle of this enlargement. The wheel could then be readily put on to the shaft, and when the key was driven up contact was made over nearly one half the surface and the periphery ran dead true. I remember seeing this feature much admired in London, and several times heard the remark, “I should think the key would throw it some.”

To prevent fanning I made the fly-wheel and pulley with arms of oval cross-section. These have always been used by me. They have done even better than I expected. They are found to impart no motion to the air, however rapidly they may be run.

Flanges on the Eccentric.Flanges on the Strap.

Flanges on the Eccentric.

Flanges on the Strap.

As already stated, the Allen valve-gear required the position of the eccentric to coincide with that of the crank, so that these should pass their dead points simultaneously. To insure this and to make it impossible for the engineer to advance his eccentric, which he would be pretty sure to do if he could, I made the eccentric solid on the shaft. This also enabled me to make it smaller, the low side being brought down nearly to the surface of the shaft. The construction, moreover, was substantial and saved some work.

All eccentrics that I had seen were flanged on each side to keep the strap in place. I observed the oil to work out freely between the flanges and the strap. This action would of course be increasedin high-speed engines. So I reversed the design, as shown in the above sections of these two bearings at the top of the eccentric, putting the flanges on the strap instead of on the eccentric.

It will be seen that the more rapid the speed the more difficult it becomes to keep the oil in the first bearing, and the more difficult it becomes for it to get out of the second one. I ought to have adopted the same construction for the main shaft journal, but in all the years I was making engines it never occurred to me. I contented myself with turning a groove in the hub of the crank, as shown to prevent the oil from getting on the disk.

The problem of crank-pin lubrication at high speed at once presented itself and had to be met. I finally solved it in the mannerpartially shownon page 54. A wiper was bolted on the back of the crank, and from it a tube entered the diagonal hole in the pin. This always worked perfectly. This wiper and the oil cup are shown on page 230. Other devices have been employed by various makers of high-speed engines, but I always adhered to this one. It has the advantage of being equally applicable to double-crank engines. Aside from the above features, the design for my exhibition engine was made by Mr. Richards.

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