Compound steam engine

“ In the case of power plant work, it is now the practice to use compound engines for the large sizes, while triple expansion engines are more commonly employed in pumping stations. Many designs of multiple expansion engines are provided with chambers between the cylinders, called receivers. In engines of this type the exhaust is frequently reheated in the receivers by means of brass coils containing live steam. In the case of a cross-compound engine, a receiver is always used. ”

“ The next important step in maritime progress, following the adoption of iron and the screw, was taken about 1870, when the compound engine came into general use. Though the compound engine had been used on a small vessel in France as early as 1829, it was first extensively adopted as the result of the rapid development in steam navigation which took place in the seventies. In the compound engine the steam, instead of being used in only one cylinder in passing from the boiler to the condenser, exerts its force in two or three cylinders, and even in four, in the quadruple expansion engines. ”

“ Steam at a very high pressure enters the high-pressure cylinder, expands and escapes at a lower pressure into a larger cylinder where it again expands and does more work. A compound engine is more economical in steam than a simple engine, and therefore requires a smaller boiler to develop the same horse-power, so that when we consider the weight of water and fuel for a given time, together with the weight of the boiler and the engine, the engine motor with a compound engine is lighter than a simple engine. ”

“ One of the greatest reasons for the increased speed of these new ships was the introduction of the compound engine. It was in 1854 that John Elder, a Briton, adapted the compound engine to marine uses. This improvement, by utilizing more thoroughly the expansive power of steam, increased at one stroke the power developed by engines without increasing [Pg 90] the supply of steam. The principle of the compound engine is simple. Steam escaping from the single cylinder of a simple steam engine still retains a part of its pressure—that is, a part of its power to expand. ”

“ The demand for increased speed led to higher steam pressure and greater engine speed. The range of economical expansion in one cylinder being limited, the tri-compound or triple-expansion engine was designed to utilize the increased boiler pressures. The gain was two-fold. The new engines, using a higher pressure of steam, were lighter than their predecessors of equal power and they were also more economical. ”

“ The highest type of modern steam engines is to be found in the compound multiple-expansion engine, in which three or more cylinders of different diameters with corresponding pistons are so arranged that steam is made to act first upon the piston in the smallest cylinder at high pressure, [115] and then discharging into the next larger cylinder, called the intermediate, acts expansively upon its piston, and thence, passing into the still larger low pressure cylinder, imparts its further expansive effect upon its piston. ”

“ It may be said that, all things considered, therefore, losses of heat in the steam-cylinder are least when the steam enters dry, or moderately superheated, where the interior surfaces are kept hottest by the steam-jacket or by the hot-air jacket sometimes used, and where piston-speed and velocity of rotation are highest. [115] The best of compound engines, using steam of seventy-five pounds pressure and condensing, usually require about two pounds of coal per hour—20,000,000 foot-pounds of energy at the furnace—to develop a horse-power, i. ”

“ I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner as the pressure of the atmosphere is now employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the open air after it has done its office. ”

“ They do come together, however, at last, and then follows the excitement of the trial. There is nothing more striking in the history of the construction of a steam engine than this, that there can be no partial or private tests of the work by the workmen in the course of its progress—but every thing remains in suspense until all is complete, and the ship and the machinery are actually ready for sea. The immense and ponderous masses which constitute the elements of the mighty structure are hoisted slowly on board and let down into their places. ”

“ Imagine the effect on an engine which is putting out its whole strength and getting full charges of fuel, if the belt suddenly slipped off and it were "allowed its head." A burst fly-wheel would be only one of the results. The steam-engine is easily controlled by the centrifugal action of a ball-governor, which, as the speed increases, gradually spreads its balls and lifts a lever connected with a valve in the steam supply pipe. Owing to its elastic nature, steam will do useful work if admitted in small quantities to the cylinder. ”

“ The reduction of coal-bunker capacity is largely compensated by the increase of economy secured by superheating, by increased expansion, elevation of piston-speed, and the introduction of surface-condensation.
A good marine steam-engine of the form which was considered standard 15 or 20 years ago, having low-pressure boilers carrying steam at 20 or 25 pounds pressure as a maximum, expanding twice or three times, and having a jet-condenser, would require about 30 or 35 pounds of feed-water per horse-power per hour ”

“ It is one of the remarkable things in the history and development of mechanism, that in this day of perfected steam engines, the inventors of our time should go back and utilize the principles employed in the first recorded steam engine, namely, the turbine. Instead of pressure exerting a force against a piston, as in the reciprocating engine, the steam acted by impacting against a moving surface, and by obtaining more or less reaction from air-resistance against a freely discharging steam jet or jets. ”

“ For small horsepowers, such as are required for pumping, feed grinding, churning, etc., the gas engine is so much more convenient and so very much cheaper in operation than the small steam engine that it is safe to say that within a very few years the gas engine will have completely displaced the small steam engine. In fact, the discovery of the gas engine permits the same economies for the small engine that the progress in steam engineering has made possible for the large steam engine. ”

“ The steam-engine is a machine of reciprocating, converted into rotary, motion by the crank. The progress of mechanical engineering during the nineteenth century is measured by the improvements of the steam-engine, principally in the direction of saving fuel, by the invention of internal combustion or gas-engines, the application of electrical transmission, and, latest, the practical development of steam turbines by Parsons, Westinghouse, Delaval, Curtis, and others. ”

“ To be sure Watt, the mathematical instrument-maker, had invented the double-acting steam-engine, but few had been manufactured, and those in common use were "atmospheric" engines, known as "Newcomen's" engines. A pumping-engine had a long, vertical cylinder, with arrangements for admitting steam at the top. The weight of the piston, piston-rod, and pump-rod, which ran down a shaft to the lowest point in the mine, being balanced by a counter-weight on a sort of well-sweep, the steam, admitted by hand, forced the piston to the bottom of the cylinder. ”

“ A steam-engine, doing the same work, would be ready for action at all times, could be applied, when not driving the vessel, to raising the anchor, working the pumps, and to ventilating the ship, while the fire would also serve to cook with. The engine would occupy less space and weight than the men, would require less aliment, and that of a less expensive kind, etc. He would make the boiler safe against explosions by bands of iron ”

“ Aside from the economy secured through using superheated steam, there is an important advantage arising through the fact that it materially reduces the erosion of the turbine blades by the action of water that would be carried by saturated steam. In using saturated steam in a steam turbine or piston engine, the work done on expanding the steam causes condensation of a portion of the steam, so that even were the steam dry on entering the turbine, it would contain water on leaving the turbine. ”

“ If the properties of steam are present to your mind, you will perceive at a glance that the economic working of Newcomen's engine seems to require two irreconcilable conditions. When the piston descends, the cylinder is required to be cold, otherwise it meets some steam there, still very elastic, which retards the operation very much, and diminishes the effect of the external atmosphere. ”

“ The steam-engine itself, which supplies us with such unbounded power, owes its present perfection to this most admirable means of giving to metallic objects the most precise and perfect geometrical forms. How could we, for instance, have good steam-engines if we had not the means of boring out a true cylinder, or turning a true piston-rod, or planing a valve face? ”

“ Nevertheless, as the transportation of passengers on railroads is found to be attended with less liability to loss of life or injury of person than their carriage by stage-coach, it will be found, very probably, that the general use of steam in transporting freight on common roads may be attended with less risk to life or property than to-day attends the use of horse-power.
The Steam Fire-Engine is still another form of portable engine. It is also one of the latest of all applications of steam-power. The steam fire-engine is peculiarly an American production. ”

“ When the engines were first made, the steam escaped into the atmosphere, and made comparatively little noise; it was found difficult then to produce steam in sufficient quantity to keep the engine constantly working, or rather to obtain an adequate rapidity of current in the chimney to give sufficient intensity to the fire. To effect a greater rapidity, or to increase the draught of the chimney, Mr. Stephenson thought that by causing the steam to escape into the chimney through a pipe with its end turned upward, the velocity of the current would be accelerated, and such was the effect ”

“ The superior simplicity and lightness of the high-pressure engine must now be apparent, and these qualities recommend it strongly for all purposes in which the engine itself must be moved from place to place.
The steam-engine therefore consists of two distinct parts,—the boiler, which is at once the generator and magazine of steam, and the cylinder with its piston, which is the instrument by which this power is brought into operation and rendered effective. ”

“ When this difficulty has been overcome, and that it will be overcome there can be no manner of doubt, gas engines will rapidly displace the steam engine, because a gas engine with a gas producer, producing gas from any ordinary coal with the same ease as steam is produced from a boiler, will be much safer, and will use one-half the fuel of the very best steam engines for equal power. The first cost also will not be greater than that of steam. The engine itself will be more expensive than a steam engine of equal power, but the gas producer will be less expensive than the boiler at present. ”

“ The governor is usually attached to a throttle-valve in the steam-pipe, an arrangement which is not the best possible under variable loads, but which produces no serious loss of efficiency when the engine is driven, as at competitive trials, under the very uniform load of a Prony strap-brake and at very nearly the maximum capacity of the machine. The most successful engines have had steam-jacketed cylinders—always an essential to maximum economy—with high steam and a considerable expansion. ”

“ But that this step will be greatly aided by any material change in the marine steam engine in the very near future is not probable, the difficulty is now not with the engine but with the boiler; forced draught and the higher pressures call imperatively for a new development in the steam producer; leaky tubes and joints and a rapid deterioration through the effort to keep up the high pressures necessary for the successful performance of the new type of engine are the shortcomings which must be successfully combated before we can make another great advance. ”

“ The high pressure steam engine in its stationary form is almost ubiquitous in America. In all great iron and steel works, in all factories, in all plants for lighting cities with electricity, in brief, wherever in the United States great power in compact form is wanted, there will be found the high pressure steam engine furnishing all the power that is required, and more, too, if more is demanded, because it appears to be equal to every human requisition. ”

“ The steam-engine is the finest example of the mechanical art. A thousand parts make up the whole, all of which move together in harmony. The most violent storm never disorders them. The piston moves, the crank turns, the steam rises, and is condensed. It is nothing but the Marquis of Worcester's kettle boiling over, Papin's rod or piston, Watt's crank, improved by later inventors. ”