Farm motors, steam and gas engines

Front matter

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Class JTeTj^ZS Hook -P ~T

COPYRIGHT DEPOSIT.

Preface To Second Edition

The first edition of this book was published in 1913. It was new in its field and the experience since gained in teaching farm motors has led to the present revision.

In this edition the chapters on gas and oil engines and on traction engines were enlarged, the steam engine chapters were rewritten and new chapters were added on automobiles and on animal motors. All other chapters were revised.

In the preparation of this edition, the author is particularly indebted to President J. H. Waters and to his colleagues N. A. Crawford, W. A. Buck, E. V. Collins and F. A. Wirt of the Kansas State Agricultural College. A. A. Potter.

Manhattan, Kansas, April 10, 1917.

Preface

In preparing this book it has been the intention to include the fundamental principles governing the construction, working and management of motors which are suitable for farm use. The motors treated include steam engines, gas and oil engines, traction engines, automobiles, water motors, windmills and electric motors.

The method followed in each chapter was to give:

1. the fundamental principles underlying the particular motor,

2. the principal parts of the motor,

3. auxiliary parts,

4. uses to which the particular type of motor is adapted.

5. selection, erection and management of the different machines. While this book was prepared primarily as a text-book for

students in agricultural engineering, the subject matter is so presented that it will be of equal value to farmers and to operators of various kinds of engines and motors. Much practical information is included regarding steam, gas and electricity, and the text is illustrated with over 275 cuts.

Some space is devoted to the more refined methods used in engineering practice for improving the economy of various motors. While many of these methods are not used at the present time in connection with farm motors, it is the opinion of the author that a knowledge of the best engineering practice is not only of considerable educational value, but will lead to the more perfect manipulation of the simple farm motors.

The successful rural engineer of the near future will be the man that applies proven engineering to the machinery and constructions used on the farm.

The author is particularly indebted in the preparation of this book to Professors E. B. McCormick, M. R. Bowerman, R". A. Seaton, and W. W. Carlson, of the Kansas State Agricultural College; to Professors Allen and Bursley of the University of Michigan; and to Mr. S. Yesner of Boston, Mass.

A. A. Potter.

Manhattan, Kansas, November, 1913.

Contents

Page

Preface v

CHAPTER I Farm Motors in General 1

Sources of energy — Principles governing the action of various mechanical motors — Animal motors — Comparison of various types of motors — Power used on farms — Comparative cost of power with various motors — Problems.

CHAPTER II Fundamental Principles and Definitions 6

Matter — States of matter — Motion — Force and pressure — Work, energy and power — Horsepower — Indicated horsepower — Brake horsepower — Draw-bar horsepower — Nature of heat — Temperature — Thermometers — Units of heat — Mechanical equivalent of heat — Specific heak — Specific gravity — Problems.

Chapter III

Theory of steam generation — Fuels — Combustion — Commercial value of fuels — Principal parts of a steam power plant — Classification of boilers — Return tubular boiler — Vertical fire-tube boilers — Water-tube boilers — Grates for boiler furnaces — Piping for boilers — Pipe fittings — Valves — Safety valves — Steam gages — Water glass and gage cocks — Water column — Steam traps — Feed pumps and injectors — Feed-water heaters — Chimneys and draft-producing systems — Firing — Rating of boilers — Management of boilers — Problems.

Chapter IV

Description of the steam engine — Action of the plain slide valve — Types of steam engine valve gears — Valve setting — Steam engine indicator cards — Losses in steam engines — Steam engine governors — Engine details — Lubricators — Steam separators — The steam lo- ' comotive or Buckeymobile — Steam turbines — Installation and care of steam engines — Problems.

x CONTENTS

Page

Chapter V

The internal-combustion engine — The gas engine cycle — Classification of gas engines — The four-stroke cycle — The two-stroke cycle engine — Comparison of two-stroke cycle and four-stroke cycle engines — Gas engine fuels — Gasoline and other distillates of crude petroleum — Alcohol as a fuel for gas engine use — Essential parts of a four-stroke cycle gas engine — Carburetors for gasoline engines — Carbureting kerosene and the heavier fuels — Cooling of gas engine cylinder walls — Gas engine ignition systems — Electric ignition systems for gas engines — The make-and-break system of ignition— The jump spark system of ignition — Ignition dynamos — Magnetos — Low-tension magnetos — High-tension magnetos — Timers — Automatic ignition for oil engines — Lubrication of gas and oil engines — Governing of gas engines — The gasoline engine on the farm — Selecting a gas engine — Installation of gas engines — Instructions for operating gas engines — Care of a gas engine — Problems.

CHAPTER VI Automobiles 122

Types of automobiles — Essential parts of a gasoline automobile Automobile motors — Clutches — Transmission gears — The progressive sliding-gear transmission system — The selective sliding-gear transmission system — The planetary transmission system — The friction drive — Differentials for automobiles — Universal joint — Front and rear axles — Steering and control systems — Brakes — Wheels and tires — Carburetors and gasoline feed systems — Ignition —Automobile lubrication — Automobile starting systems — Automobile lighting and accessories — Management of automobiles — Gasoline motor cycles — Problems.

Chapter VII

Fundamental parts of a traction engine — Steam traction engines — Boilers — Pumps — Feed-water heaters — Engine types — Reversing mechanisms for steam traction engines — Steering — Transmission systems and differentials — Gas traction engines — The gas traction engine motor — Carburetors for traction engines — Ignition for gas traction engines — Transmission systems and differentials — Type of traction — Uses of traction engines — Development of the gas traction engine — Economy of gas traction engines — Rating of traction engines — Operation and care of traction engines — Problems.

CHAPTER VIII Determining the power of streams — Types of water motors — Over

CONTENTS xi

Page

shot, undershot and breast wheels — Impulse water motors — Water turbines — The hydraulic ram — Problems.

Chapter IX

Types of windmills — Principal parts of a windmill — The wind-wheel — The rudder or vane — The governor — Windmill gearing — Windmill brake — Towers — Method of erecting windmills — Care of windmills — Power of windmills — Uses of windmills — Problems.

CHAPTER X Electric Motors, Generators and Batteries 236

Action of electricity — Units of electricity — Ohm's law — Incandescent lamps — Wires for conductors of electricity — Electrical batteries — Primary batteries — Storage batteries — The lead storage battery — The Edison storage battery — Methods of connecting batteries — The electric generator — Action of the electric generator — Direct and alternating currents — Principal parts of generators and motors — Classification of generators and motors — Series-wound generators — Series-wound motors — Shunt-wound generators — Shunt-wound motors — Compound-wound generators — Compound-wound motors — Various types of motors compared — Distribution of electric current — Electric meters — Fuses and circuit breakers — Switches and rheostats — Method of connecting motors — The electric motor on the farm — The farm electric light plant — Installation of electric motors and generators — Starting and stopping motors — Starting and stopping generators — Care of motors and generators — Problems.

CHAPTER XI Animal Motors 272

The horse — Selection of a draft horse — Capacity and power of draft animals — Selection of feed for the horse — The mule — The ox — Cost of animal power — Problems.

Chapter XII

Belts — Leather belts — Rubber belts — Canvas belts — Care of belts — Method of lacing belts — Pulleys — Method of calculating sizes of pulleys — Quarter-turn belt — Chain drives — Rope transmission — Friction gearing — Toothed gearing — Shafting — Problems.

Index 293

Chapter I Farm Motors In General

A motor is an apparatus capable of doing work. Not considering animal motors, which include men, horses and other animals, the mechanical motors available for farm use are: heat engines, including steam, gas, oil, hot-air and solar engines; pressure engines such as waterwheels and water motors; windmills; electric motors.

Sources of Energy. — The principal source of all energy is the sun. It causes the growth of plants which furnish food for man and animals. The great coal deposits are only the result of the storing up of the sun's rays in plants in bygone days. These rays are also responsible for the raising of water from sea level to mountain top, thus giving it energy which can be utilized to turn waterwheels and made to do useful work.

On the other hand, while the sun's rays are the fundamental sources of all energy, they can be utilized directly by man only to a very limited extent. The secondary sources of energy are the wind, waterfalls, carbon in different forms, such as coal, petroleum, or gas, and chemicals used in electric batteries.

Principles Governing the Action of Various Mechanical Motors. — All mechanical motors do work by virtue of motion given to a piston, to blades on a wheel, or to an armature by some substance such as water, steam, gas, air, or electricity. The first requirement is that the above-mentioned substance, often called the working substance, be under considerable pressure.

This pressure in the case of the water motor or waterwheel is obtained by collecting water in dams and tanks, or by utilizing the kinetic energy of natural waterfalls. The total power available in water when in motion depends on the weight of water discharged in a given time, and on the head or distance through which the water is allowed to fall. The head of water can be utilized by its weight or pressure acting directly on a piston or on blades or paddles on wheels.

Considering next the various forms of heat engines, work is accomplished by steam or gas under pressure, this pressure being obtained by utilizing the heat of some fuel or of the rays of the sun.

A motor utilizing the heat of the sun is called a solar motor or a solar engine. The action of this type of motor depends on the vaporization of water into steam by means of the rays of the sun, which are concentrated and intensified by means of reflecting surfaces.

In the case of the steam engine a fuel, like coal, oil, or gas, is burned in a furnace and its heat of combustion is utilized in changing water into steam, at high pressure, in a special vessel called a boiler. This high-pressure steam is then conveyed by pipes to the engine cylinder where its energy is expended in pushing a piston as in the case of the reciprocating engine. The sliding motion of the piston may be changed into rotary motion at the shaft by the interposition of a connecting rod and crank. Another method is to allow the high-pressure steam to escape through a nozzle, strike blades on a wheel and produce rotary motion direct, as in the case of the steam turbine.

In another type of heat engine, called a hot-air engine, air is heated in a cylinder by a fuel which is burned outside of the engine cylinder, and by its expansion drives a piston and thus does work.

In the case of gas and oil engines the fuel, which must be in a gaseous form as it enters the engine cylinder, is mixed with air in the proper proportions to form an explosive mixture. It is then compressed and ignited within the cylinder of the engine, the high pressures produced by the explosion pushing on a piston and doing work. These engines belong to a class called internal-combustion engines, and differ from the steam and hot-air engines, which are sometimes called external-combustion engines, in that the fuel with air is burned inside the engine cylinder, instead of in an auxiliary apparatus.

The windmill derives its high pressure for doing work from the moving atmosphere.

FARM MOTORS IN GENERAL 3

The electric motor converts electrical energy at high pressure into work; this electrical pressure or voltage is produced in an apparatus called an electrical dynamo, or generator.

Animal Motors. — The animal can be considered as a motor to which fuel is supplied in the form of food. This food furnishes energy required for the operation and maintenance of the various organs and processes within the animal body, as well as for the production of mechanical work. The animal body is, in fact, a combination of complex mechanisms, in every one of which heat is produced and work is performed.

Comparison of Various Types of Motors. — The solar motor is but little used on account of its high first cost and great bulk in relation to the small power developed.

In localities where the wind is abundant and little power is needed, the windmill is the most desirable and cheapest power. The greatest application of windmills is for the pumping of water for residences and farms, and for such other work as does not suffer from suspension during calm weather. Electric storage and lighting on a small scale from the power of a windmill has been tried in several places with fair success, but probably will not be adapted to any great extent on account of the high first cost of such an installation.

The water motor or water turbine is very economical if a plentiful supply of water can be had at a fairly high head, but its reliability is affected by drought, floods and ice in the water supply.

The hot-air engine, while not economical in fuel consumption, is well-adapted for pumping water in places where the cost of fuel is not an important item and where safety and simplicity of mechanism are essential. The hot-air engine, on account of its high cost, bulk and poor fuel economy, has been largely superseded by the oil engine, which uses gasoline or the heavier oils.

Of the other forms of heat engines, the internal-combustion engine, whether using gas or oil, is well-adapted for small and medium-sized powers, such as for farm use and irrigation work. The oil traction engine has also a very important field on the modern farm.

For the generation of electricity, and in large sizes, the steam engines or steam turbines will be found more suitable on account of their lower first cost and great reliability. The steam engine is also used successfully on large traction engines.

If a source of electric current is available at a low price, the electric motor is very desirable, as it requires little care and can be bought in sizes to suit all requirements.

Of the animal motors, the horse is the most important. Unlike mechanical motors, the horse is self -feeding, self -reproducing and self -maintaining. For very short intervals, animal motors are capable of considerable overload capacity, but are expensive, require constant care and can work effectively only for short periods of time. With animal motors, the amount of power under the control of one man is much less than in the case of mechanical motors. The mechanical motor requires fuel only when actively at work, while the animal motor requires feed at regular intervals whether working or not.

Power Used on Farms. — About 25 million horses and mules are available for power purposes on the farms of the United States. This represents available animal power to the amount of about 16 million horsepower. The power available in mechanical farm motors will probably exceed 10 million horsepower. The total amount of power used on farms thus represents more than 25 million horsepower, or the power which is available on farms is about one-third greater than the total amount of power used by all the manufacturing industries of this country.

Comparative Cost of Power with Various Motors. — Varying character and prices of both feed for animal motors and fuel for mechanical motors will affect the cost of power in different localities. Ordinarily, the power produced by animal motors is more expensive than that developed by the use of mechanical motors. Experiments indicate that with the horse as a motor, the cost of power per horsepower per hour will vary from 5 to Q}4 cts. With stationary gasoline engines, the cost of power will vary from 1J^ to 2}^ cts. per horsepower per hour; with kerosene fuel, from % to 1 ct.; with fuel oil, less than 1 ct. per horsepower per hour. With steam engines a horsepower per hour can usually be produced for about 1 ct.

Problems: Chapter I

1. What is a motor? Name four types of mechanical motors.

2. Name the principal source of all energy. Explain in detail.

FARM MOTORS IN GENERAL 5

3. What are the fundamental principles which govern the action of vari* ous mechanical motors ? Illustrate how the principle is applied in the case of waterwheels, steam engines, gas engines, windmills, electric motors.

4. Compare various types of mechanical motors as to their adaptability for use on the farm.

5. Discuss the relative advantages and disadvantages of mechanical motors and of animal motors.

6. How does the power available on American farms compare with the power used in the manufacturing industries of this country?

Chapter II Fundamental Principles And Definitions

Before a study is made of any motor, the fundamental conceptions of physics regarding states of matter, work, power and heat are essential.

Matter. — Matter is that which occupies space and, when limited in amount, it is called a body. Matter in any form consists of a great many small particles, called molecules, the relative position of which determines the state in which a substance exists.

States of Matter. — Matter exists in the solid, liquid and gaseous states.

In the case of the solid the relative positions of the molecules are fixed. A solid having a certain shape or form, whether due to natural or artificial causes, will retain that form, unless and until it is made to change the same by some external cause.

In the liquid, the relative positions of the various molecules are not fixed. The shape or form of a liquid depends, therefore, on the solid walls surrounding it, a liquid assuming the form of any vessel in which it may be placed.

In the case of a gas the various molecules struggle to occupy greater space. A gas can be greatly compressed by an external force, and will expand to a considerable extent, if it is given perfect freedom.

Motion. — Motion means change of place. If a definite amount of matter, called a body, is removed from one place to another, motion is produced.

Force and Pressure. — Anything which produces or tends to produce, modifies or tends to modify motion is called force. Force is measured in pounds. Pressure is the intensity of force and is equal to the total force divided by the area over which it acts. For example, a force of 1,000 lb. acting on a bo.dy whose dimensions are 5 by 2 in., will produce a pressure or intensity of force equal to the force divided by the area of the body in

square inches, or ' = 100 lb. In English and American practice, pressure is always expressed in pounds per square inch. Thus when a steam gage on a boiler is registering 80 lb., this means that the steam is capable of transmitting a force of 80 lb. for every square inch on which it acts. If it is allowed to act on a 12-in. piston, the area of which is 113.1 sq. in., the total force exerted on the piston is 80 time's 113.1 or 9,048 lb.

The pressure exerted by the atmosphere is called barometric pressure. The barometric pressure is 14.7 lb. per square inch at sea level and decreases as the altitude, or the height of the surface of the earth above sea level, increases. For each 2,000 ft. in elevation the pressure of the atmosphere is decreased by about 1 lb. The barometric pressure plus gage pressure equals absolute pressure.

Work, Energy and Power. — Work means force times distance through which it acts and is independent of time. If a body of 1 lb. is raised through a distance of 1 ft., the resulting work is 1 ft.-lb.

The capacity for doing work is called energy. Energy existing in a body at rest, as in the case of the raised weight, is called potential energy. Energy possessed by a body when in motion is called kinetic energy.

As an illustration, a cubic foot of water, weighing 62.5 lb. when at rest at a height of 100 ft., has potential energy of 6,250 ft.-lb. and this potential energy is changed into kinetic energy of work when the water is allowed to fall through that height. The water in the above example when allowed to fall through 10 ft. will be capable, on account of its kinetic energy, to do 625 ft.- lb. of work and will have a potential energy of 6,250 — 625, or 5,625 ft.-lb. when it comes again to rest.

Power takes into consideration the time required to do a certain amount of work and is defined as the rate of doing work. Thus if steam at a pressure of 100 lb. moves a piston 18 in. in diameter through a distance of 2 ft., the work done is 100 times 508.92 (the area of the piston in inches multiplied by the distance in feet) or 50,892 ft.-lb. The power of the engine, however, depends on the time that the steam requires to move the piston through the given distance and, if the motion is accomplished in 1 sec, the power of the engine is five times greater than if 5 sec. were required.

Horsepower. — If work is done at the rate of 33,000 ft.-lb. per minute, 1 hp. is said to be exerted. This means that an engine will have a capacity of 1 hp. if it can do 550 ft.-lb. of work in a second, 33,000 ft.-lb. of work in a minute, or 1,980,000 ft.-lb. of work in an hour. To determine the horsepower developed by any motor or engine, it is necessary to find the foot-pounds of work which the motor or engine is doing in a minute and divide this by 33,000. In the example of the previous paragraph if the piston passes through the distance of 2 ft. in }£o min.; the power of the engine in horsepower is

It is important to remember that power takes into consideration work and time. All animals, including man, are able to produce more power for a short period of time, while mechanical motors, whether driven by water, wind, steam, gas, or electricity can exert, with proper care, the power for which they are designed for an indefinite length of time.

Indicated Horsepower. — The term " indicated horsepower" (i.hp.) is applied to the rate of doing work by steam or by a gas in the cylinder of an engine, and is obtained by means of a special instrument, called an indicator. One form of this type of instrument, the Crosby, is shown in section in Fig. 1. It consists essentially of a cylinder (4), which is placed in direct communication with the engine cylinder, and in which moves a piston(8) compressing a spring above it and raising the arm (16). At the end of the arm is a pencil (23) which records graphically the pressure of the steam in the engine cylinder on the revolving drum (24). This drum (24) is covered with paper and receives its motion from the engine crosshead. From the diagram drawn on the drum of the indicator, the average unbalanced pressure is determined, and the horsepower is calculated from this and from dimensions and speed of the engine.

As an illustration: Given the average unbalanced pressure of the steam on a 12-in. piston, as obtained by means of an indicator, and called the mean effective pressure, 40 lb. per square inch; then the total pressure exerted by the steam is

Total pressure = 40 X 113.1 = 4,524 lb.

If the stroke of the piston is 13 in., the work done in foot-pounds per stroke is

If the engine speed is 250 r.p.m., the work per minute will be, if the engine is single acting,

Fig. 1. — Steam engine indicator.

Since 33,000 ft. -lb. per minute is 1 hp., the power of the engine when single-acting is

1,225,250

33,000

As steam engines are usually double-acting, an indicator card would have to be taken of the crank end, the unbalanced or the mean effective pressure determined for that end and the indicated horsepower calculated by the above method, taking into consideration the size of the piston rod. The total indicated horsepower of the engine is the sum of that calculated for the two ends.

Brake Horsepower. — Brake horsepower represents the actual effective power which a motor or engine can deliver for the purpose of work at a shaft or a brake, or transmit to a belt for stationary work, such as threshing or the driving of machines. An instrument for the measurement of the brake horsepower of motors, and called a Prony brake, is shown in Fig. 2. This brake consists of two wooden blocks BB which fit around the pulley P

Fig. 2. — Prony brake.

and are tightened by means of the thumb nuts NN. A projection of one of the blocks, the lever L, rests on the platform scale S. When the brake is balanced, the power absorbed is measured by the weight as registered on the scales, multiplied by the distance it would pass through in that time if free to move. If I is the length of the brake arm in feet, w the weight as registered on the scales, in pounds, and n the revolutions per minute of the motor, the horsepower absorbed can be calculated by the formula

2wlwn Brake horsepower = ~» ~~~

As an illustration, the scale reading of an engine running at 250 r.p.m. is 80 lb. If the length of the brake arm is 5)4 ft., calculate the brake horsepower developed.

Drawbar Horsepower. — The belt or the brake horsepower minus the power required to propel the weight of a traction engine or power vehicle is called the drawbar horsepower. Ordinarily, a traction engine will require about 50 per cent, of the total power developed by its motor, to move the traction engine. This means that the drawbar horsepower, available for plowing or for pulling implements, is about one-half of the total power developed by the motor.

Nature of Heat. — Heat is a form of energy and not a material substance. The heat of a body depends on the vibratory motion of the particles or molecules of which the body is built up; the greater the rate of motion of these molecules the higher is the temperature of the body.

Temperature. — Temperature indicates the relative heats of bodies, or the relative rates of motion of the molecules in bodies. Temperature is not a measure of the amount or quantity of heat in a body. Thus a small and a large piece of metal may be heated to the same temperature, but the large piece would possess the greater quantity of heat. Temperature is an indication of the sensible heat of a substance, or the heat intensity which can be revealed to the senses of an observer.

Thermometers. — A thermometer is an instrument by means of which the temperature of a substance is measured. As usually constructed, it consists of a liquid such as mercury or alcohol inclosed in a bulb at one end of a thin glass tube, the temperature changes producing sufficient variations in the expansion of the liquid to be read off on a scale attached to, or graduated on, the glass tube.

Thermometers are graduated in three different ways, which are called the three thermometric scales, the type of scale depending on the number of graduations, or degrees (° denotes degree), between the melting-point of ice and the boiling-point of water.

The scale mostly used in English-speaking countries is the Fahrenheit (F.). In this case the melting-point of ice is taken at 32° and the boiling-point of water at 212°. Thus the Fahrenheit degree (°F.) is }{ go of the interval between the two fixed points.

In scientific work the Centigrade scale is used in most countries. The Centigrade degree is Jloo of the temperature interval between the melting-point of ice and the boiling-point of water, these two fixed points being denoted 0°C. and 100°C. respectively.

Another scale, used only to a limited extent in certain countries of Europe is the Reaumur scale, which has the melting-point of ice at 0°R. and the boiling-point of water at 80°R.

The relations existing between the thermometric scales mostly used, i.e., the Fahrenheit (F.) and the Centigrade (C), can be expressed :

degrees C. = % (degrees F. —32) degrees F. = % degrees C. +32 Example: Convert 15°C. to the Fahrenheit scale and 400°F. to the Centigrade scale.

Table 1 can be used for converting Centigrade into Fahrenheit degrees and conversely.

Units of Heat. — Heat is measured in heat units. A heat unit is the amount of heat required to raise the temperature of 1 lb. of water 1°. The heat unit used in English-speaking countries is the British thermal unit (B.t.u.). The B.t.u. is defined as the amount of heat required to raise 1 lb. of water from 62°F. to 63°F.

When a certain illuminating gas is said to contain 600 B.t.u., this means that each cubic foot of the gas is capable of raising the temperature of 10 lb. of water through 60°F., or that it will raise the temperature of water so that the product of the weight of water and temperature rise (in °F.) is 600.