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Steam Engine Frequently Asked Questions

Modified on 2012/01/09 13:55 by Joel Havens Categorized as Steam Engines
Ques. What is a steam engine?
ANS. It is an apparatus for converting heat into mechanical power, or more plainly, an ingenious machine worked by steam.

Ques. What is a stationary steam engine?
ANS. An engine which is erected in a certain location and designed to remain in the same position, without change, or more plainly, it is an engine which does its work without changing its place.

Ques. What is a marine engine?
ANS. It is an engine designed for propelling steamships, either screw or side wheelers.

Ques. What is a locomotive engine?
ANS.. An engine designed to operate on iron and steel railways. With engine and boiler combined in one machine it becomes a " traveling engine."

Ques. Are there any other steam engines than these three?
ANS. Yes. Portable engines, hoisting engines, the steam hammer, the steam drill, pumping engines, blowing engines, steam fire engines, donkey, steering engines, etc.

Ques. Do these all operate on the same general principle or law, and what is that?
ANS. Yes. The underlying principle or law of nature regulating the building of all these is that which applies to the formation and expansion of gases. Water is changed into gas (steam) by the heat of combustion, and while such, is subject to the laws which govern the expansion, contraction, etc., of all gases.

Ques. Where does the power or energy which drives all steam engines come from?
ANS. From the coal or other fuel.

Ques. Does any of the power come from the steam, water or engine?
ANS. Not any. The power or energy comes from the heat and the heat comes from the burning of the coal. It is the property of an engine that it must continuously get back to a starting point and at each half revolution it gains a fresh supply of energy (heat) to be expended in its appointed work.

Ques. How many types or forms of steam engines are there?
ANS. Very many hundreds, if not thousands, but all operated upon the principles as stated.

Ques. What is the most numerous pattern?
ANS. The common slide valve, stationary engine.

Ques. What type of engines are now leading the advance in economy and effectiveness?
ANS. The automatic cut-off engines are fast superceding and replacing the common slide valve engines.

Ques. Upon what point are the maker, the buyer and the engineer of a steam engine all agreed?
ANS. Upon the matter of its " running" quality.

Ques. What could be considered a fair "running" requirement in a new engine, in the hands of a first-class engineer?
ANS. A satisfactory running engine is one which has the stationary parts of such strength and security that there is absolutely no movement at any point due to the reciprocating of the moving pieces. In an engine which is perfectly satisfactory in this respect, a slender rod with a squared end, such as a common lead pencil, can be placed in a standing position on a level surface at any point and remain there indefinitely without other support than its own base.

Notes.—There are very many places from which the slide valve engine will never be displaced, as, from places where fuel is cheap, such as saw and planing mills, etc.; also where an engine has to be started and stopped at frequent intervals, such as first motion hoisting engines.

Ques. What quantity of coal is now considered to be "good practice" per horse power, per hour?
ANS. Very few stationary steam engines have developed a performance of less than 2 pounds of coal per horse power per hour, and 5 pounds is a common consumption of coal for that amount of work. In marine expansion engines—multi-cylinder—the rate has been often reduced below i 1/3 lbs. per horse power per hour.

Ques. About how much of the heat generated in the furnace is utilized in useful work?
ANS. About ten per cent. Some engines upon careful measurement have shown only seven per cent. The waste of heat that forms such a large aggregate common to every steam engine begins at the furnace and only ends with the steam passing out of the exhaust port.

Ques. What attainments should be looked for in a modern steam engine?
ANS. Close regulation of speed; the least conduction of heat from the steam by the cooling of the cylinder; small clearances; free steam openings from steam chest to cylinder, to allow full boiler pressure to enter the cylinder up to the point of cut-off; free exhaust, allowing no back pressure through any fault of the engine; rapid motion of valve at point of cut-off to make such point decisive; tight valves, allowing no waste of steam by leakage; and last, but exceedingly important, the least possible friction in the valves and moving parts of the engine.

Note.—Whatever the grade of material of which the parts are constructed, whatever their strength, however perfect their design and finish, the engine fails of being wholly satisfactory if its running qualities are in any respect imperfect. An engine to be perfectly satisfactory should be capable of sustaining a maximum load without heating either in the main bearing, crank pin, crosshead pin, or guides; and, furthermore, it should do this without any noise of knocking as the centres are passed; likewise all the reciprocating parts should operate noiselessly and without jar or trembling.

Ques. What is the meaning of the term "cycle “?
ANS. If a substance like water or gas be subjected to various changes by the action of heat and finally brought back to its original condition it is said to have undergone "a cycle of operations."

Ques. What is the true measure of the efficiency of an engine?
ANS. The proportion of the heat converted into work in pushing the piston is the measure of the engine's efficiency.

Ques. How are steam engines rated?
ANS. By horse power. Ques. What is a horse power? ANS. 33,000 foot-pounds per minute, 550 foot-pounds per second, or 1,980,000 foot-pounds per hour.

Ques. What is a foot-pound?
ANS; One pound of force exerted through one foot of space.

Ques. Is it correct to say "horse power per minute," "horse power per hour," etc.?
ANS. No. If an engine is doing work at the rate of 50 horse power it is doing 50 horse power all the time. It is an error which is frequently made to assume that such an engine is doing 50 horse power per minute, for 50 X 60 — 3,000 horse power per hour.

Ques. What is a self-contained engine?
ANS. The self-contained engine is entirely dependent upon its own frame to hold all its parts together, and does not need a solid foundation.

note.—If the steam reaches the piston at 145 pounds above the atmosphere, the heat is about 363 degrees Fahr.; when expanded down to 30 pounds above the atmosphere, the temperature falls to about 247 degrees Fahr.; so that about 90 degrees of the heat generated has been utilized. This seems a small proportion, but it can never be made much greater. The losses from too much clearance, from initial condensation and re-evaporation of condensed steam towards the end of the stroke, may be reduced by intelligent engineering, but there are no prospects that the supreme loss of heat present in the exhaust steam will ever be overcome.

Ques. What is a "right-hand engine"?
ANS. An engine the fly-wheel of which is to the right, as looked at from the cylinder.

Ques. What is a left-hand engine?
ANS. An engine the fly-wheel of which is to the left, as looked at from the cylinder.

Ques. What is meant by an engine running " over "?
ANS. The top of the wheel running away from the cylinder.

Ques. What is meant by an engine running " under "?
ANS. The top of the wheel running toward the cylinder.

Ques. Which way are engines more generally run?
ANS. Over.

Ques. What advantages pertain to running an engine in this way?
ANS. The pressure of the cross-head is always downward upon the guide, for when the pressure is on the head end of the piston the thrust against the connecting rod which is pointing upward reacts to press the cross-head down upon the guides; and when the pressure is on the crank end of the cylinder, the cross-head will be dragging the crank, and as the crank is below the center line, it will still pull the cross-head down upon the lower guide. If on the other hand the engine is run " under," the thrust of the cross-head will be upon the top guide on both the outward and inward strokes, and unless the cross-head is nicely adjusted to its guides, and the guides are perfectly parallel under running conditions, the cross-head will be lifted when subjected to thrust, and fall by its own weight on the centers, making the engine pound.

Note.—The non-self-contained engine is one which is partly depending on the foundation to hold some of its parts in place, as for instance the outward pillow block and crank shaft. The foundations of such engines have to be particularly well designed. Most of the high speed and vertical engines belong to the former class, while the long stroke, slow and medium speed with girder or tangeye bed, and also soma vertical engines belong to the non-self-contained engines. In stationary engineering, there are more single high pressure engines used than any other kind. These, when of a good design and well taken care of, can be very economical.

Ques. When is it desirable to have an engine run tinder?
ANS. When it is impossible to so locate the engine as to give the proper direction to the belt from an "over' running wheel.

Ques. What is a "single valve" engine?
ANS. An engine in which a single valve controls the admission and distribution of steam for both ends of the cylinder; as in a common slide valve engine.

Ques. What is a "four valve engine?
ANS. An engine having a separate steam and exhaust valve for each end of the cylinder, as a Corliss engine.

Ques. What is a single acting engine?
ANS. An engine in which, like the Westinghouse, the steam acts on one side of the piston only.

Ques. What is a rotary engine?
ANS. It is one in which piston and crank are formed in one place connected to the shaft and rotating in a chamber. The piston instead of returning to its starting point continues turning in one direction. It is an ordinary engine which does not work upon the principle of expansion.

Ques. What is the meaning of the terms "automatic " and "automatic engine"?
ANS. Automatic means self-acting—in machinery, it describes certain movements commonly made by hand which are made by the machine itself. Hence, an automatic engine is a self-regulating engine.

Note. —
There is good reason for believing that the steam engine is now as nearly perfect as it will ever be made, unless someone discovers a new method of transmitting the power from the boiler to the driven mechanism. That some revolutionary method will be discovered is highly improbable, and so engineers must content themselves to go on improving on details and stopping leaks that defective designs leave open. Meanwhile, about 90 per cent, of the heat generated in the furnace will continue to pass out through the smokestack and exhaust port, and science will continue to look on, impotent to stop or lessen this immense waste of energy."

Ques. What are the reciprocating parts of the engine?
ANS. All those parts which move to and fro are the reciprocating parts; 1, the piston; 2, the piston rod; 3, the crosshead; and 4, the connecting rod. The connecting rod is attached to the crosshead, the crosshead to the piston rod, the piston rod to the piston and this latter is actuated directly by the steam pressure.

Ques. What is the action of these various parts?
ANS. They begin from a state of rest at the commencement of the stroke and are gradually set in motion, slowly at first, and faster and faster until the middle of the stroke, when they are moving with the same velocity as the crank pin. After that their motion is retarded until the end of the stroke, when they again come to rest and the same action is repeated. It thus becomes necessary for the crosshead to come to rest at the beginning and end of each stroke.

Ques. Into what two classes are engines divided with reference to the manner in which they are governed?
ANS. Throttling, and automatic cut-off.

Ques. Into what two classes may the automatic cut-off engines be divided?
ANS. The single valves, in which the point of cut-off is varied by changing the amount of travel of the valve, and the four-valve engines, in which the cut-off is usually effected by a detaching mechanism or trip under the control of the governor.

Ques. What is the difference in principle of operation between an automatic cut-off and slide valve throttling engine?
ANS. The automatic cut-off engine regulates its speed by cutting off the steam at an earlier point of the stroke; this allows the steam to work by expansion, increasing the economy; the pressure thus reduced in the cylinder by expansion will regulate the speed. The slide valve throttling engine regulates its speed by throttling the steam between the boiler and the cylinder.

Note.—The end of one stroke is the beginning of another, and two makes one revolution of the engine.

Ques. What particular advantages are claimed for vertical or upright engines?
Ans. A decrease in frictional resistance, especially on the pistons; an increased economy due to the thorough draining of the cylinders; they require less floor space for given power; they are more easily accessible in many of their parts, especially as to valves, stuffing boxes and pistons. Cylinders standing vertically do not corrode on their wearing surfaces, i. e., those parts sustaining the greater wear; their cylinders are less liable to accident from flooding with water from steam and exhaust pipes.

Ques. What are the special advantages claimed for the high speed engine?
ANS. It is said that in high speed engines the uniformity and smoothness of running is much better than it is in slow speed engines owing to the greater quickness of the action of the automatic governor with which they are equipped— hence also more perfect regulation; 2, the moving parts are comparatively lighter, with larger wearing surfaces; 3, they are more compact, using less space for the same power; 4, the direct action and simplicity of parts; 5, less in cost for the same power; 6, they are in line with modern advance.

Note.—That these advantages are becoming more clearly recognized with each year is evident from the development of the high speed engine since its first introduction. At the International Exposition in Vienna in i873, the average piston speed of the engines there exhibited was [about 350 feet per minute and the maximum about 420 feet per minute, while the same makers exhibited in i888 at the Vienna Industrial Exhibition, engines whose average piston speed was about 480 feet per minute and a maximum of nearly 700 feet per minute. At the International Exposition in Paris in i889, piston speeds of 780 feet had been attained and at the Electrical Exposition in Frankfurt, in i89i, the maximum was 875 feet per minute. In large engines to day, 900 feet per minute is not considered excessive, and we find even in small electric lighting engines of the type known as high speed engines, meaning high rotary speed, that between 700 and 800 feet per minute is the ordinary piston velocity.

Information Sources

  • New catechism of the steam engine 1902 pages 17-24

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