Power

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Preface

^ It is the object of the series of lectures included in this

volume to point out the enormous effect that the substi- (o tution of mechanical power for hand and animal labor has had on the organization of society and the conditions of living, and by presenting the development of power machinery to show what sort of ideas have produced this result. The effect of power machinery is soon told and readily understood ; but it is not so easy, though far more important, to show how the men who are responsible for what has been done have thought and worked, and with what kind of things and with what reasoning those men must deal who are to take up the responsibility for future ' progress. The bulk of the subject-matter, accordingly,

^1^ is concerned with the apparatus and machinery for the

converting of natural energy in any of its available forms into useful work, together with the physical processes for the execution of which that apparatus was devised.

\j» hi* Li* r

I i

Contents

L The Relation of Mkchanical Power and Ma-

CHINERY TO SOCIAL CONDITIONS .... 11^

II. Means EMPLOYED for the Substitution of Power

II Means Employed For The Substitution Of Power

FOR THE LABOR OF MEN

In the story of the development of power machinery, the part played by the rods, shafts, cylinders, and other elements of the mechanism as arranged and rearranged, important as it is, is subordinate to the ideas or conceptions of the physical processes that each rearrangement of well-known parts is devised to carry out.

should be treated to give the most work, than to make a steam-engine that will run ; more important to know how combustible gas mixed with air should be treated to give an explosion with the highest possible pressure, than to make a chamber strong enough to hold the exploding mixture without breaking. GeneraUzing, it may be said that knowledge of what should be done is more important and of higher order than mere abiUty to make a mechanism that will work after a fashion.

Each process as it was conceived added a fact to man's understanding of physical nature, and in turn contributed to the discovery of the next. Air and water in motion, being capable of moving wheels with paddles, naturally lead a student to inquire how fluids, water, air, steam, etc., may be put in motion, a question which, once conceived, almost instantly answers itself, — by allowing them to escape from high-pressure chambers. The next logical step is to inquire how fluids may be prepared so as to have high pressures in chambers from which they may escape, and this leads to the discovery that water may be boiled in closed vessels by fire outside, or that explosions of powder and gaseous fuels may be caused to take place, or, more simply, that water may be led in pipes from the upper level of a waterfall to the lower level; and at once the three characteristic systems of power generation are understood, — water-power, steam-power, and gas-power systems. Experience with high-pressure fluid results in an understanding of its tendency to push apart the inclosing walls, one of which may be movable and on which the pressure may alternately act, as it moves back and forth, and there is in consequence developed the idea of another way of securing motion from fluids under pressure, besides the older one of jets striking paddle-wheels. An almost infinite number of combinations of mechanism parts and constructive details can be found to carry out each process, so that the processes are fundamental and the mechanisms incidental. It must not be understood, however, that these several parts may have infinite variety of form, or that they may be made of any convenient material, for there are limitations which must not be ignored. The mechanical elements must have such simple form as to be easily made by the shop tools and workmen ; both the form and material of each part must be suitable for the purpose in strength, stiffness, flexibility, or wearing qualities; and the whole machine must be neither too costly to produce or to keep in repair, nor require too skilful an operator to manage.

The problem of power-machinery development is, therefore, divisible into several parts: First, what processes must be carried out to produce motion against resistance from the energy of winds, the water of the rivers, or from fuel. Second, what combinations of simply formed parts can be made to carry out the process or series of processes. These two steps when worked out will result in some kind of an engine, but it may not be a good engine, for it may use up too much natural energy for the work it does ; some part may break or another wear too fast; some part may have a form that no workman can make, or use up too much material or time in the making; in short, while the engine may work, it may be too wasteful, or do its work at too great a cost of coal or water, attendance in operation, or investment, or all these together. There must, therefore, be added several other elements to the problem, as follows: Third, how many ways are there of making each part, and which is the cheapest, or what other form of part might be devised that would be cheaper to make, or what cheaper material is there that would be equally suitable. Fourth, how sensitive to care are all these parts when in operation, and how much attendance and repairs will be required to keep the machine in good operating condition. Fifth, how big must the important parts or the whole machine be to utiUze all the energy available, or to produce the desired amount of power. Sixth, how much force must each part of the mechanism sustain, and how big must it be when made of suitable material so as not to break. Seventh, how much work can be produced by the process for each unit of energy supphed.

In the early days of power generation all these elements of the power problem were not recognized, but they were developed and studied about in the order named, a fairly satisfactory solution of the first part pointing out the existence of the next and the necessity of studying it, — the solution of a new question reacting on the older so that new solutions of it appeared that could not be conceived before. It may fairly be said that this systematic study has been receiving attention for about a century and a half, but divided into periods as the study advanced to the higher stages. For example, it was not until 1860 that the seventh element of the problem was successfully treated for those power systems depending on the heat given out by fuel as the soiu'ce of energy. Although successful and commercially valuable steam-engines had been continuously produced for a hundred years, no one was able to calculate exactly how much of the heat in the steam might be converted into work by a mechanism ideally perfect, so that the goodness or badness of a mechanism could not be judged by any absolute scientific standard, but only comparatively. One engine might in operation produce a certain horse-power with less coal per hour than another, but no one could state positively why, which, of course, is the first step in rational improvement of economy; nor could the minimum possibiUties of coal consumption for a system be calculated, so that the comparative value of competing systems could not be judged. This sort of calculation is now an every-day affair, which every engineer is capable of carrying out, and is the basis of all modern designing and improvement. The fact that it took over a hundred years after building useful engines began to arrive at a scientific conception of the fundamental processes which were being more or less imperfectly executed in machines designed largely by rule of thumb is doubly significant of the high order of mental development necessary for this conception, when it is realized that the first and second elements of the problem appear to have been understood to a degree sufficient to produce working models some two thousand years before, since operative machines were built at that time, even though they were not much niore than toys.

The period of systematic and scientific power development is coincident with the true progress of the most basal of the several branches of natural philosophy, chemistry, physics, mechanics, thermodynamics, and the theory of elasticity of materials of construction; and there is no doubt that the steam-engine which was designed and built by workmen before these were formulated attracted the attention of philosophers who, in attempting to explain what took place in it, created a related body of principles by which future development was guided, and which are now the fundamental bases for the design of the future. Those men who became familiar with the natural sciences, and also with the shop methods of making machinery, and who brought both to bear on the problem of the production of machinery for specified conditions, combining the special knowledge of the scientist and shop mechanic, were the first mechanical engineers; and the profession of mechanical engineering, which is the term applied to this sort of business, was created out of the efforts to improve power systems, so as to make them more efficient and adapted to all classes of service, and to render that service for the least cost.

Nothing is more absorbingly interesting than the detailed history of power-system ideas, mechanism, and the economic production of both the machinery and the power itself, studied along with the parallel development of the natural sciences; but this is beyond the scope of these lectures, in which no more than the merest outline can be attempted, just sufficient to permit of, a little understanding of modern machinery.

As has been already said, one of the earliest understood ideas applied to power generation is that water in motion may, by striking paddles on wheels, move them and itself lose some of its motion, or that the energy of motion can be communicated from one body to another.

One of the earliest kinds of wheels based on this idea is shown in Fig. 16. The wheel was hung by its shaft, which was just a log of wood, over the surface of a fast-moving stream at such a height as would allow the paddles to dip into the water. This same fundamental idea, old as it is, is also one of the most modern, inasmuch as it is basal to the largest modern water and steam-turbines, for steam is a fluid that behaves much like water. It must not be understood that the basal idea consists in the dipping of paddles into a brook; this is a mere incident, a convenient way of carrying out the real, fundamental principle, which is that moving fluids have energy by reason of thejr motion, which energy can be imparted to wheels by bringing the original fluid to rest in a suitable way.

One of the largest water-wheels ever built, and which was designed to carry out as efficiently as possible this same idea, is shown in Fig. 17, as it appeared in the shop before shipment. The size can be appreciated by comparing it

with the men ^^ ^^

standing beside

it and on top of it. This wheel is at work below Shawinegan Falls in Canada, and develops 10,500 h. p., when supplied with water through an ll}-foot pipe from above the falls, the total effective drop being 140 feet. The vanes or curved partitions, equivalent to the paddles, areishown attached to the shaft in the pictxire of the runner, Fig. 18 Precisely the same basal principle or controlling idea is carried out, with suitable changes of structural detail, to adapt the mechanism to use steam instead of water in the steam turbine, shown in Fig, 19 as installed in the Potomac Electric Co. of Washington. Such machines as these are now built in sizes approaching 30,000 h. p. each.

In most of the modem turbines, which is the name applied to the most highly developed form of wheels designed to rob moving fluids, lite steam and water jets, of their energy of motion, there are involved many other principles or ideas, some of which are very old and some of recent conception. One of these, easy to understand, is concerned with the way in which the steam or water may be conveniently set in motion. Water, led from an elevated tank or pond by pipes to a lower level, exerts a pressure tending to burst the pipe, which is more powerful the greater the drop in level, and the pressure tends to make water flowing from a hole or nozzle move faster the greater that pressure is. Similarly, water, steam, or air, or any other fluid, confined in a chamber under pressure, will escape from that chamber through a nozzle in a jet which will have a velocity determined by the pressure. The quantity of fluid that can escape, as well as the energy of the jet, will depend on the size of the hole and velocity of the jet together. It has always been found most convenient, because of the concentration of energy that results, to devise means of getting the fluid under pressure, and then allowing it to escape to give it motion, instead of depending on substances naturally in motion. These jets of fluid may be allowed to play on vanes or paddles in a great variety of ways, giving different types of motors all known by the class name of impulse wheels, several of which, intended for water, are shown in Fig^ 20. Some of these have one nozzle and others many ; the vanes have different forms and are variously disposed on the wheels. It required many years of study, experiment, calculation, and comparison to discover just what curvature and angle should be given to these vanes and nozzles to secure high efficiency, for while any such combination as shown will run, there is only one best form for each kind, and the determination of that best form is the principal problem of the designer to-day. To such perfection has this work been carried that it is now possible to predict, within one or two per cent, how much of the fluid energy a turbine yet unbuilt will be capable of transforming into useful work. A pure impulse wheel designed to receive jets of steam is shown in Fig. 21, together with four nozzles from which the steam is escaping, striking the curved vanes of the wheel, and in passing through having its direction of motion changed to give the impulse or push.

A proper relation exists between the speed of the vanes, that of the

steam jet, and p^^ 21

the angles and

curvature that will allow the steam to leave with no velocity at all, its original energy of motion having been imparted to the wheel; and these things can now be determined with precision.

When the water issues in a fast-moving jet from a nozzle, the nozzle is pushed backward, just as a gun recoils as its projectile moves out, and this principle of reaction is used in both water-wheels and steam-turbines, either alone or associated with the impulse action. Some arrangements of mechanism working on this principle are shown in Fig. 22. In the first one the water flows outward through curved, hollow arms fixed to a hollow shaft through which the water is supplied, escaping from the outer edge or nozzle tangentially. The same action takes place but is less clearly seen in the other forms shown ; the water is, however, conducted to the working vanes or nozzles in different ways. These passages are more often a continuous row of slots than single nozzles, for the purpose of getting as much push as possible around the circumference. To all wheels in which the reaction of the jet rather than the impulse of striking vanes exerts the driving force, the class name of reaction wheels is appUed.

The antiquity of the reaction and impulse principles is shown by the records, in which it is said that one Hero, 200 B.C., or over two thousand years ago, made such a steam reaction turbine, shown in Fig. 23, in which a fantastic water vessel was heated by a fire, making steam which, flowing up two vertical standards, hollow, Uke pipes, entered a ball arranged to rotate on the ends of the standards. From the ball the steam escaped by nozzles tangentially, causing the ball to spin, to the mystification of the mass of the people, who believed that some spirit from the other world had been brought under command. A later, but nevertheless old, device, ^^^ ^^

dating from 1629 and credited to Branca, an Italian, is shown in Fig. 24. This is a pure impulse steam-turbine, coupled by toothed gearing to a shaft with lumps on it arranged to hft the pestles for crushing com or ore.

The simplest, oldest, and at once the most modern ideas for power generation are, then ; —

First, moving fluid properly directed may move wheels against resistance when it strikes vanes suitably formed.

Second, fluid under pressure may be made to acquire motion simply by escaping.

Third, jets of fluid escaping from nozzles or suitably formed passages in wheels may, by reaction of escape alone, turn those wheels.

To these principles minute and painstaking investigation, guided by progress in mathematics, mechanics, physics, and chemistry, which it no doubt assisted in stimulating as well, has added a vast body of principles of engineering, by means of which true design can be carried out, and turbines be built of predicted efficiency, of proper strength in all their parts, cheap and effective for all local situations.

While these three old principles of conversion of energy are all used in present-day turbine water-wheels and in steam-turbines, the idea underlying the more common form of steam-engine and that which may be said to have caused the industrial revolution referred to in the last lecture, the engine still most largely used on steamships and in factories and the sole dependence for locomotives, is different. It is this idea that also finds expression in all our gas, gasolene, and oil engines. This idea is based on the conception of fluid pressure as capable of exerting a push on pistons in cylinders. It was used, though not understood, by the savages, who made blow-guns, in which the hollow bamboo stick acts as a cylinder and the dart as piston; later also in powder-guns, where the gun-barrel is the cylinder and the projectile acts as piston. If a close-fitting but free-moving piston in such a cylinder be fixed to a rod, and water or steam under pressure be admitted to one end of the cylinder, the fluid pressure will push the piston if the other end of the cyhnder be open, and so move the rod.

When one end of the cylinder is open and the other closed for a working chamber, as in Fig. 25, and the closed end is fitted with two pipes, one for supplying steam, with a valve or cock to open and close communication between cylinder and supply, and the other for discharge, opening to the air, the cylinder is said to be single-acting. Closing both ends and passing the piston-rod through a close-fitting hole in one end requires the addition of another set of pipes and valves, and it is then called a double-acting cylinder, shown in Fig. 26. Two single-acting cylinders placed side by side, receiving steam from a boiler through one

SUPPLY.

SfNGLE ACTING

Fig. 25 valve, are shown in Fig. 27, as built by Leopold in 1725,

the up and down or reciprocating motion of the two piston rods working water-pumps, and the whole apparatus becomes a steam-pumping-engine. This early steam-pump uses steam at a pressure greater °°T' "2^ than the atmosphere, '

to push the piston to

the top of the cylinder, after which the steam supply

is cut off and communication with the air opened,

allowing the steam to

escape to the air as the

weight of the piston

forces it down.

This application of

the pressure idea is not

the oldest, nor was it as

widely used in its own

time as another one, in

which the steam at a

pressure about equal to

the atmosphere was

drawn into a cylinder,

and there condensed or

converted back to water

by cooling, the result^ ^la. 27

ing water of condensation occupying practically no volume compared with

the steam. The best example of the old style engine using this idea is that of Newcomen, Fig. 28. This machine had a single-acting cylinder, and the piston-rod had a chain running over the curved end of a beam to compel the rod to move in a straight hne, the other end of the beam having a weight sufficiently heavy to lift the piston, and draw into the cylinder steam from a sort of kettle having about atmospheric pressure, and, therefore, incapable of exerting any push on the piston, even when entering. At the top position of the piston the cylinder is full of steam which, having a pressure equal to the atmosphere acting on fiq. 28

the outside of the piston, has no tendency to move the piston one way or the other. Closing the steam supply valve and opening a valve in a water pipe between an elevated tank and the cylinder allows water to flow into the cylinder containing the steam, which is thereby condensed. The pressure at once falls in the cylinder to a value less than that of the atmosphere acting on the outside of the piston, the lowered pressure being called a vacuum. This vacuum, or deficiency of pressure within the cylinder below that of the atmosphere outside, allows the atmosphere to press down on the piston, movii^ it, with the rod, beam, and counterweight, back to the starting-point. The motion against resistance is, therefore, produced solely by the atmospheric pressure. There are many famiUar illustrations of this vacuum and atmospheric pressure action, commonly called suction; the ordinary act of drawing water into the mouth in drinking is a mild case, the muscular movement of the cheeks and chest producing a pressure in the mouth sUghtly less than that of the atmosphere, which forces the water inward. A still stronger suction or vacuum is required in drinking through a straw and in filling a syringe, while the ordinary barometer which measures the atmospheric pressure is only a vertical tube of mercury dipping into a cup at the bottom with a vacuum at its closed top. It is known that the most perfect vacuum resulting from the pxunping out of a glass bulb all the air it contained will enable it to suck water, as we say ordinarily, or more properly enable the surrounding atmosphere to push up water into it, through pipes from a level not more than thirty-four feet below it at sea level, which is equivalent to a pressure of 14.7 pounds on each square inch of surface. If, then, water be led into a vacuum chamber with an open pipe extending downward thirty-three feet or more into water, it would not fill the chamber but would run out, keeping the level always the same. This engine of Newcomen, which was used first in 1705 and continued at work in some places for seventy years, not only operated primarily on the vacuum, as engineers would say, or by atmospheric pressure, to be more scientific, but had a long pipe from the cylinder to allow the injected water and condensed steam to escape without assistance and automatically.

While Newcomen in his condensing atmospheric engine made use of the excess of atmospheric pressure over that of the vacuum produced by condensing steam, and Leopold made use of the excess of steam pressure over atmosphere, to do work in single-acting engines, James Watt combined the two pressure actions, getting as a result a double effect in his engine of 1784. This engine, shown in Fig. 29, marked the beginning of the building of steam-engines using the idea of pressure acting on a teciprocating piston, with mechanism to change reciprocating motion into the desired rotary motion, always under control. In it were incorporated ideas

basal to the modem locomotive, the standard horizontal and vertical engines for electric hght, street railway, and factory power stations, the modern pumping-engines for city waterworks, the blowing-engine for supplying air to. blast furnaces which extract iron from the ore, and a host of others, in almost infinite variety of detail in each of the several classes. Each of these, while having the essential pistons in cylinders, and cranks to give the rotary motion, valves and governors to control the steam, and all supplied with steam made in separate boilers from the combustion of fuel, yet has differences of structure and arrangement of parts, developed as time showed the necessity, to adapt the common essential elements to the special service. Thus, the locomotive of Fig, 30, in which the construction is clear, must contain all the elements of a complete plant supported on one frame, with as much weight on the driving wheels as possible to give adhesion. The whole machine must be rugged to stand the pounding on the rails, so all delicate mechanism must be avoided. It must be reversible, so mechanism is introduced to shift the valves by hand in addition to their normal automatic movement, and so on. The marine engine, which drives the ship, must be fairly well balanced and turn regularly without jerks, so as not to shake the ship, so that several cylinders, each with its own crank, are set side by side and the cranks set at different angles ; it must also have a light frame, so as not to reduce the carrying capacity of the vessel.

This construction is well shown in Fig. 31, illustrating the engines of the United States battlesliip Vermont in the shop of the Fore River Ship Building Co., Fore River, Massachusetts, The vessel herself is shown in Fig. 32. Questions of weight are of httle importance in stationary engines compared with steadiness and durability, but sometimes floor space is valuable, in which case a vei'tical engine of fairly heavy construction, such as shown in Fig. 33, is suitable. These engines drive the factory of Walter Baker Co. at Dorchester, Massachusetts, by electricity, the engines themselves driving electric generators, the current from which is transmitted through the factory to motors which do the work. When floor space is not valuable, the annoyance of stair climbing to reach high parts that need oiling can be eliminated and horizontal engines, such as shown in Fig. 34, substituted. The relation of engines and boilers in a large stationary electric plant, having combined vertical and horizontal piston engines, is well shown in Fig. 35, which is a cross-section of the Manhattan Elevated Railroad plant, as originally built, having a capacity of 50,000 h. p. It should be noted that the boilers are located on two stories to economize real estate, which is valuable, and the coal storage bins are placed just under the roof. Water for the condensers, located in the basement of the engine room, is supplied through tunnels leading to the river. The external appearance of the power station is shown in Fig. 36.

Two special classes of piston steam-engines, one for pumping water and the other for compressing air, and therefore called pumping-engines and blowingengines, are shown in Figs. 37 and 38. The former illustrates one of five Allis-Chalmers pumping-engines, for the Haekensack Water Company at New Milford, New Jersey, having an aggregate capacity of 72,000,000 gallons of water in twenty-four hours. The latter (Fig. 38) is a blowing-engine with a capacity of 30,000 cubic feet of air per minute at 30 pounds pressure, for the furnaces of the Republic Iron and Steel Co., and its great size is shown by comparing it with the man at the side.

To produce motion of an engine shaft from natural forms of energy, it has been shown that the first step is to so supply that energy as to get some fluid under pressure, if it is not so originally, and then to use that high-pressure fluid either to push on pistons or give itself a velocity by escaping from a nozzle, the jet impinging on vanes or reacting on the nozzle. This is true no matter how the fluid acquires the pressure.

In the water-power system advantage is taken of rivers in a hill country, and dams are constructed when necessary to collect rainfall and store water for use in dry seasons at a high level, and pipes are connected to conduct the water to a low level, at which point a pressure supply becomes available. On the other hand, in the steam system the pressure is produced by burning fuel under a boiler; while, in the gas-power system, not yet examined, the pressure is produced by explosion within the cyUnder itself, and the action of the hot high-pressure gases that result from it is always by direct pressure of these gases on a piston. Curiously enough, however, the high pressures obtainable by explosions of suitably prepared fuel were not at first directly used, but instead the heat of the combustion was made the means of getting the atmospheric pressure to act, just as the atniospheric steam-engine preceded that using high-pressure steam. In 1860 Huygens exploded gunpowder in a cylinder having a piston, the hot gases escaping from the cylinder through open valves which were closed as soon as the internal pressure equaled that of the atmosphere ; then the hot gases were cooled and in cooling lost pressure, producing a partial vacuum exactly as did the condensing of steam in Newcomen's cylinder. Atmospheric pressure forces the piston inward, giving motion, from the combustion of fuel directly without any steam intervention, but the effect is feeble and no successful gas-engine would ever have been built if study had stopped there. It required a lot of time to connect the idea of the common gun, using high gas pressure from the explosion of solid gunpowder fuel, with the piston engine idea. It did not come about until the realization that combustible gases mixed with air would produce an explosion resulting in high pressure, that could be used to act on a piston, and which could be controlled quite as well as steam. It is probable that the old notion of explosion being connected with destruction had a good deal to do with the delay. After a series of proposals deaUng with explosive gas and air mixtures, beginning about 1825, there finally was produced, but not before