## Dimensioned Lumber

The lumber industry uses two different sizes, nominal size and actual size. The nominal size is the dimensions of the lumber after it is sawed. The actual size is the size of the lumber after the surfaces have been finished. Finishing removes material, therefore the actual size is smaller than the nominal size, Table 24.1. Lumber is purchased using the nominal size, but the actual size must be used for beam calculations. An additional term may also be used and that is rough sawed or unfinished....

## Introduction

In some applications, such as a push lawn mower with a vertical crankshaft engine, the power is used at the location that it is produced. The blade is attached directly to the end of the crankshaft. Most machines require a more complex system for transporting the power from the source to the load. In addition, many machines require that the power produced by the motor or engine be modified and or transported to another part of the machine. These modifications could include changing the speed of...

## Displacement

Displacement is the cylindrical volume that a piston displaces as it moves through one stroke. It is equal to the area of the piston multiplied by the length of the stroke. Displacement is one of the factors that determine the amount of horsepower an engine will produce, the greater the displacement, the greater the volume of air and fuel that is burned during combustion, which means more power. Expressed mathematically, piston displacement is where PD Piston displacement in cubic inches (in3)...

## Using Units in the Metric SI System

A major problem with the customary units is that there is no logical relationship between units. For instance, there is no obvious reason why the standard mile is 5,280 ft. The metric system was created in the late 18th century by the French to address this problem. One of the advantages of the SI system is that all of the units are based on natural phenomena. For example, a meter is the distance light travels, in a vacuum, in 1 299,792,458th of a second. The U.S. agricultural industry is based...

## Costs of Machinery

This section discusses those elements that contribute to the cost of owning and operating agricultural machinery. An understanding of the types of costs and their impact on the profitability of the enterprise improves our ability to make meaningful decisions regarding the management of agricultural equipment. It is best to base decisions on the actual costs of the machine. Good managers will record the annual costs for machines, but unfortunately the total costs are not known until a machine...

## Odometer

An odometer is a mechanical device that records revolutions. An odometer wheel has an odometer and a drive train that records the distance traveled, Figure 12.1. The common odometer wheel counts the revolutions of a wheel and shows the distance traveled on a multiple dial readout, Figure 12.2. The dial can be designed to produce readings in whole feet, decimal feet, feet and inches and meters. The principle of an odometer wheel is circumference of a wheel times the number of FIGURE 12.2....

## Tractor Power Ratings

Different power ratings are used to evaluate the size of tractors and engines. It is important to remember that manufactures like to advertise their engine power with the highest possible number to make them competitive in the marketplace. The useable power is usually less than the advertised power. The type of value used to express the power must be known before the useable power can be determined, Figure 7.1.

## Four Stroke Cycle

The four-stroke cycle engine, commonly called 4 cycle engine, is one of the two common types of engine cycles used for both spark and compression ignition engines. In 4 cycle engines, the eight events occur during four strokes of the piston or two revolutions of the crankshaft. The four strokes are called Study Figure 5.2 and the following description of the events. During the intake stroke, the intake valve opens, and the piston travels from the top of the cylinder (TDC) to the bottom (BDC)....

## System Capacity

System capacity is the maximum amount of water that an irrigation system can deliver on a continuous basis. Different units are used to describe system capacity. These are acre-feet (ac-ft, that is, the amount of water it will take to cover one acre, one foot deep), acre-inch (ac-in), gallons per minute (gal min or gpm), and cubic feet per second (ft3 sec or cfs). The required pumping capacity of an irrigation system depends on the area to be irrigated (ac), the depth of water to apply (in),...

## Types of Engines

The two primary categories of engines are the spark ignition (Otto-cycle) and the compression ignition (Diesel-cycle). In the spark ignition engine, the fuel is metered and introduced into the engine by either a carburetor or an injection system, Figure 5.5. When a carburetor is used, the fuel is metered by jets and orifices in the carburetor and added to the air as it flows through the venturi of the carburetor. Mixing occurs as the fuel-air mixture moves through the intake system and into the...

## Lever Resultant

A lever is a rigid bar, straight or curved, capable of being rotated around a fixed point (fulcrum). When a fulcrum and a bar are used, two different forces exist, the applied force (Fa) and the resultant force (Fr). The forces, bar, and fulcrum can be used in three ways, called classes, Figure 4.1. FIGURE 4.1. Three classes of levers. FIGURE 4.1. Three classes of levers. The principle of levers can be expressed mathematically as Force Arm Force Arm V Applied V Applied Resultant Resultant Class...

## Trapezoid

A trapezoid is a four-sided figure with only two parallel sides. Note that the height must be measured perpendicular to the parallel sides, Figure 13.14. The area of a trapezoid is determined by the equation where A Area h Height (distance between the parallel sides) a Length of one parallel side b Length of the second parallel side. Problem What is the area (ac) of a trapezoid with parallel sides of 300.0 ft and 450.0 ft, and with a height of 120.0 ft Solution (using conversion to acres)...

## Metes and Bounds

The metes and bounds system is based on a verbal or written description of the boundary using land marks visible at the time. The description includes a point of beginning (POB), such as a rock, tree, stake, or post, and lengths and bearings of successive lines from this point. Lengths may be paces or in units of chains, poles, or rods. As the technology available for surveying improved, these units were replaced by feet and inches, decimal feet or metric measurements. The bearings may be...

## Sizing a Pneumatic System

The capacity and the horsepower requirements of pneumatic conveyors depend on eight factors 1. The horizontal distance that the material is moved. 3. The vertical distance that the material is moved. 4. The number of bends in the pipe. 5. The elevation above sea level. 6. The temperature of the outside air. 7. The type of material being conveyed 8. The moisture content of the material. To size a pneumatic system the effect of each of these factors must be accounted for. Table 20.3 is an example...

## Objectives Of Leveling In Agriculture Engineering

Be able to list the criteria for selecting tractors and machines. 2. Be able to determine optimum machine size. 3. Be able to calculate ownership and operating costs of agricultural equipment. 4. Understand ways to reduce the costs of owning and operating tractors and machinery. 5. Understand the concept of break-even use (BEU) for a machine. 6. Be able to calculate BEU for a machine. 7. Understand the importance of regular maintenance of agricultural machinery.

## Surveying Equipment

The equipment used in leveling consists of a leveling instrument and a leveling rod. The most common type of level is called an engineer's or a dumpy level. The leveling instrument is a telescope containing both vertical and horizontal crosshairs and one or more spirit levels (bubble in a liquid-filled tube) to indicate when the instrument base is horizontal. The entire assembly, consisting of the frame, telescope and spirit level, can be leveled by turning the three or four leveling screws...

## Performance Efficiency

Performance efficiency refers to the quality of work done by a machine. The importance of a performance evaluation is not the same for all machines. For example, the quality of the job for primary tillage, like plowing, is not as critical to the profitability of the farming enterprise as the quality of the job for a combine. In addition, it would be very difficult to mathematically evaluate the quality of plowing. For a harvesting machine, performance efficiency is a measure of the actual...

## Series Circuit

In a series circuit the electricity has no alternative paths. All of the electricity must pass through all of the components in the circuit, see Figure 26.1. For the electricity to leave and return to the source it must pass through all three loads, resistors. In a series circuit the total resistance of the circuit is the sum of each resistance where the unit or resistance in the Ohm (ft). Rt R1 + R2 + R3 + + RN The total resistance of the circuit in Figure 26.1 is Rt 2.5 ft + 3.2 ft + 4.0 ft...

## Circuit Protection

An important part of any circuit is the over current protection fuse or circuit breaker. Over-current devices are used to prevent the conductors from overheating. Remember when electricity passes through a resistance, heat is produced and a voltage drop occurs. As the electrical load on a circuit increases, the heat produced increases and the voltage drop increases. An electrician determines the total amperage capacity of the circuit and then installs the appropriate over-current protection. In...

## Grounding

To simplify the earlier discussion of circuits only two conductors were used, hot and neutral. To meet current wiring codes a complete wiring system uses at least three conductors hot, neutral, and ground. The ground conductor (equipment ground) is attached to the case of metal-cased tools and it must provide a complete low resistance circuit to the earth, Figure 26.10. This is usually accomplished by attaching it to the grounding bar in the service entrance panel. If a short occurs between the...

## Combining Machines

All agricultural machines are a combination of these five simple machines. The analysis of the forces on a complex machine exceeds the objectives of this text, but Figure 4.17 is an example of how two or more of these machines can be used together. This example is also useful for discussing the problem solving process. The first inclination is to try and solve for the amount of weight first. If this approach is FIGURE 4.17. Two machines working in combination. FIGURE 4.17. Two machines working...

## Diagrams and Sketches

Some problems involve the determination of a quantity of items, such as the number of nails per sheet of plywood or the number of studs in a wall. In solving these types of problems it usually is helpful to draw a sketch or a diagram. Problem How many posts are needed to build a fence 100 ft long with posts 10 ft apart Solution For many people the first response would be 10 but a diagram, Figure 1.1 shows that the correct number of posts is 11. This is an example of a situation where a wrong...

## Precision Accuracy and Uncertainty

It is important to understand three characteristics of numbers in solving agricultural problems precision, accuracy, and uncertainty. Precision refers to the size of the unit of measure used to obtain the number. For example, if a sack of feed is weighed on a scale measuring to the nearest 0.1 lb, the weight is not as precise as it would be if the smallest unit of measure was to the nearest 0.01 lb. The accuracy of a number refers to the number of decimal places obtained in the answer. The...

## Electrical Terms

To understand electricity and how it functions, it is important to understand common electrical terms and their definitions. Current Current is the movement of electrons through a conductor. The amount of current moving is determined by the voltage divided by the resistance. Alternating current (AC) One of two types of electric current, alternating current does not exhibit constant polarity or a constant voltage. The voltage builds to a maximum value in one polarity, declines to zero, builds to...

## Theoretical Power

In the previous chapter, theoretical power was defined as the calculated horsepower based on the bore, cylinder pressure, and engine speed. Figure 5.8 shows a typical cylinder pressure curve for a naturally aspirated engine. During the intake stroke the pressure is below zero, atmospheric. The pressure starts to rise as the compression stroke occurs and jumps rapidly at combustion. During the power stroke and exhaust stroke, the cylinder pressure gradually drops back to zero. The average...

## Force

Force is that action which causes or tends to cause motion or a change of motion of an object. To describe a force completely, its direction of action, magnitude, and point of application must be known. What is commonly referred to as a force is really two forces, as forces are never present singly, but always in pairs. The two parts are called action and reaction. They are always of equal magnitude, but in opposite directions. In this text, the weight of an object will be considered a force....

## Principles of Testing

Because of the important role tractors play in agricultural production, accurate information is a must for efficient management of the modern farm and ranch. Any information is usable, but the main objective of testing is to provide standardized results so that comparisons can be made between different models and different years. The primary purpose of tractor testing standards is to establish the test conditions and the rules of behavior for the manufacturer and the testing station. It should...

## Sprocket Sizes

Roller chains and sprockets, Figure 6.3, have two advantages over belts and pulleys. They are capable of transmitting greater amounts of power, and because it is impossible for the chain to slip, the sprockets stay in time. The equation used with pulleys can be used to determine sprocket sizes by replacing the diameter of the pulley with the teeth for each sprocket. For sprockets, FIGURE 6.3. Roller chain and sprockets. FIGURE 6.3. Roller chain and sprockets. Problem A hydraulic pump will be...

## Measuring Distances

Several methods and devices can be used for measuring distance. The principal ones are 3. taping or chaining 6. electronic distance measuring (EDM) One of the decisions that must be made when preparing to measure a distance is selecting the method or device to use. The following sections will discuss each of these devices and help the user make that decision. First, it will be helpful to review the common units of distance (displacement). The common English units are as follows 1 foot (ft) 12...

## Recording Field Notes

Engineers and surveyors have developed a standard practice for recording surveying information because it is important that the notes be clear, complete and easy to read. Professional surveyors use electronic instruments when every possible. These instruments record the data and down load it to a data collector or computer for post processing and or use. On electronic instruments the manufacturers of the equipment establish the process and form for collecting and recording the data. For small...

## Significant Figures

The principle of significant figures is important because the precision of a number should not be increased by mathematical computations. Calculators routinely carry 7 to 14 decimals places on screen and or in memory even though the accuracy and precision of measurements are only two or three places. It is usually necessary to determine the number of digits that should be kept in a number after mathematical computations. The rules for determining significant digits are different for exact and...

## Type of Service

The type of engine service is determined by the load-intermittent or continuous. An intermittent load on an engine is a load that varies in torque and speed for example, tractors in tillage operations are subject to intermittent loads. Continuous loads provide little variation in the torque and speed demands placed on the engine irrigation pumps are an example of a continuous load. Some manufacturers may indicate the type of service for the rated power. If not, the engine should be derated for...

## Electricity

Electricity is the flow of electrons from one atom to another. Scientists believe that electricity was first noted when ancient people discovered the attraction between an amber rod and other materials. An understanding of electricity begins with the atom. Electrons travel in orbit around a nucleus composed of protons and neutrons. When an atom has the same number of protons and electrons, it has no charge. When it has more electrons than protons, it has a negative charge, and if more protons...

## Objectives

Be able to list and describe the events that occur in an internal combustion engine. 2. Be able to describe how a spark ignition (Otto-cycle) engine differs in operation from a compression ignition (Diesel-cycle) engine. 3. Be able to diagram and describe the events that occur in sequence during each stroke of a four-stroke cycle engine. 4. Be able to diagram and describe the events that occur in a two-stroke cycle engine. 5. Given the bore, stroke, number of cylinders, and clearance volume, be...

## Mathematical Problem Solving

Mathematical problem solving is the process by which an individual uses previously acquired knowledge, skills, and understanding to satisfy the demands of an unfamiliar situation. The essence of the process is the ability to use information and facts to arrive at a solution. There are two characteristics of problem solving that must be remembered when solving problems using mathematical processes. 1. The mathematical process does not always give you the answer just more information so that you...

## Three Sides

The second type of triangle is one where the lengths of the three sides are known, Figure 13.10. This method for determining the area of a triangle is easier to use because the only measurements are the three sides of the triangle. The shape of the triangle doesn't influence the difficulty in completing the measurements. The primary limitation of this method is the requirement of measuring the length of all three sides. This method cannot be used if one or more of the side lengths cannot be...

## PTO Power

Power take-off power (ptohp) is a rating of the power available at the power take-off of an agricultural tractor. Power take-offs are used to supply rotary power to many different types of machines such as balers, pumps, and mowers. To determine PTO power either power equation using torque can be used. where hp horsepower To torque (lb-ft) N speed (rpm) where kW kilowatts To torque (Nm) N speed (rpm).

## Pulley

A pulley is a modification of a first or second class lever. A single pulley does not produce any mechanical advantage, just a change of direction in force, Figure 4.13. If the power loss to friction is not ignored, then a single pulley has a mechanical advantage of less than one. When pulleys are combined in pairs, a mechanical advantage is produced. This use of pulleys is commonly called a block and tackle, Figure 4.14. The amount of mechanical advantage produced by a block and tackle is...

## Seasonal Need

Seasonal water demand is the amount of water (in inches) that a crop must have during one growing season for maximum production. The seasonal water demand will vary from season to season, and for each crop and region. Table 19.4 contains some typical values for three regions of the United States. Knowledge of the seasonal water demand for a crop in a given area is useful for determining the contribution of irrigation to the cost of production and the total amount of water that will be needed....

## Air Conditioning

In some types of buildings, ventilation may not be adequate to maintain the optimum temperature. The amount of heat produced by the animals, the processing, outside temperatures and so on, may exceed the ability of the ventilation system to maintain the desired temperature. In these situations, air conditioners are used. Historically many different systems were used to condition the air. Cooling with ice, pumping well water through a radiator, evaporative cooling, or drawing air through...

## Time of Concentration

The time of concentration for a watershed is defined as the time required for water to flow from the most remote point of the watershed to the outlet. The peak rate will occur when the entire watershed contributes to the runoff. The peak runoff flow is influenced by many factors. For the purposes of this text, the only factors that will be considered are slope and length of the drainage way. Obviously, if the drainage way is short and steep, the water will arrive at the outlet quickly and the...

## Voltmeters

Two characteristics of circuits must be remembered in using voltmeters (1) Voltage is the measurement of a potential between two points so the reading on a voltmeter is the difference between the connection points. To reduce the effect of adding a voltmeter to the circuit, the meter is constructed with a very high internal resistance. (2) Anytime that electricity flows through a resistance heat is produced and the loss of energy causes the voltage to decrease. This decrease is called the...

When a load is applied to a simple beam, the beam tends to bend. As the beam bends or flexes, the fibers along the bottom surface of the beam are stretched (put in tension), and the fibers along the top surface of the beam are pressed together (compressed). It is important to remember that the opposite is true for a cantilever beam. with a cantilever beam, the top stretches and the bottom is compressed. As the fibers of a beam stretch, a stress is set up in the fibers. When beam loading and...

## Erosion Control

The best philosophy for erosion control is that it is better to prevent erosion than to try to correct it. There is no best solution for erosion control that will work in all situations. Erosion prevention and control must be developed for each site using the resources that are available. On cultivated land, the best methods to use are those activities that will reduce the effect of wind and water on the soil particles. For the prevention of water erosion it is important to provide as much...

## Throughput

The concepts of theoretical and effective capacity also are applicable to throughput capacity. Throughput is based on time, but because throughput usually refers to the flow of material through a machine, the units may be different from those used for capacity. For example, the performance of a hay baler could be evaluated using units of bales per hour or tons per hour. Problem What is the throughput of a baler if it baled 150.0 tons in one week while operating an average of 6.0 hr per day...

## Metric Problems

Problem Determine the theoretical capacity for a 20.0-m wide cultivator traveling at 9.6 km hr. km 1,000 m 1 ha 9.6 x 20.0 m x --x Problem What is the effective capacity for the cultivator in the previous problems if the operator wasted 0.75 hr per 10.0 hr working day Solution The first step is to solve for the time efficiency. output Efficiency ( ) x 100 input Problem How many hours will it take to cultivate 20.0 ha with an 8.0-m cultivator traveling at 10 km hr Assume a field efficiency of 85...

## Electronic Distance Measurement EDM

EDM instruments determine lengths based on the time that it takes for an energy wave to travel from one end of a line to the other and return. They have replaced the difficult and painstaking task of taping for accurate measurement of horizontal distances. They also can measure distance over bodies of water or other inaccessible terrain as long as they have a clear line of sight. Some require a reflective surface to bounce the beam back, some are reflector less. Others use a second unit to...

## Foresight

A foresight (FS) is a rod reading taken on any point of unknown elevation. In differential leveling, there is only one foresight for each instrument setup, whereas profile leveling may have several foresights per instrument setup. The FS is subtracted from the HI to find the elevation of an unknown point. In Figure 15.3, the foresight rod reading, 3.21 ft, is subtracted from the instrument height, 105.01 ft to determine the elevation at the unknown point, 101.8 ft.

## Moisture Management

Water and its addition to or removal from agricultural products and materials is an extremely important topic in nearly all aspects of agriculture. The moisture contents of grain, feed, or hay to be bought or sold, of crops to be dried, or of meat and dairy products to be processed are but a few examples of products where moisture must be carefully managed. Moisture may be added to or removed from the product depending upon the desired final condition. Moisture is removed from products by...

## Setting up a Surveying Level

Many different types and variations of levels are used for surveying. The following procedure for setting up an engineer's level will also work with most other types. When not in use, the instrument is housed in a case for protection. To be used, it must be removed from this case and carefully threaded on the tripod head. The tripod legs are set about 4 ft apart and pushed firmly into the ground, thereby FIGURE 15.7. Reading the rod using a target. providing a stable base for the instrument and...

## Pulleys

Parts of a V-belt system. FIGURE 6.1. Parts of a V-belt system. the diameter of the driver pulley times the speed of the driver pulley is equal to the diameter of the driven pulley times the speed of the driven pulley. Expressed mathematically the pulley equation is where D Diameter of a pulley N Pulley speed in revolutions per minute. This statement is true because the linear speed (feet per minute) of the belt remains constant. If we identify D1 as the diameter of the driver...

## Capacity

The trend in agriculture has been to larger farms. This trend has increased the demand for machines with larger and larger capacity. A previous chapter discussed that the options for increasing capacity are using a wider width, operating at a faster speed (both requiring more power) and increasing efficiency of operation. It also is important to be able to complete the operation in a timely fashion. Unfortunately, information on the timeliness of agricultural operations is limited. Some...

## Rvalues and Uvalues

Two different numbers are used to describe the insulating properties of construction materials R-values and U-values. The R-value is a number that represents the thermal resistance of a material. The lvalue is a measurement of the thermal conductivity of a material. In the customary units, a lvalue of 1 means that 1 BTU hr of heat will flow per square foot of area per degree difference in temperature on each side of the material. The term BTU stands for British Thermal Unit, and is the amount...

## Break Even

Rate of 21.00 per acre the cost for an annual use of about 60 acres per year it is more economical to hire work. At annual use of over 60 acres per year it is more economical to own the machine and do the work yourself. This same method can be used to determine the beak-even point for costs with units different than dollars per acre. For the process to result in good information the custom rate and the total costs must be in the same units. The BEU can be determined by the following equation...

## Storage of Biological Products

The term biological products has been used throughout this chapter because products such as grains, fruits, and vegetables are living organisms. Because they are alive, there are minimum requirements for moisture, temperature, and air to maintain their viability but the life of the product can be extended if the temperature or moisture or air is modified during storage. The challenge for managers of many such products is to extend the storage life of the product without damaging its viability,...

## Belts and Pulleys

Two different techniques can be used to change the direction of rotation, Figure 6.4. Notice that twisting the belt changes the direction of rotation. This technique is acceptable if the pulleys are some distance apart, the belt is operating at slow speed and it is not transmitting a large load. The belts will rub at the center and these three conditions will increase the amount of friction at that point. The friction produced from rubbing will shorten the life of the belt. The addition of a...

## Two Types of Erosion 1851 Water

The amount of erosion caused by water is dependent on four factors climate, soil, vegetation, and topography. The impact of climate is related to the amount and the intensity of rain. The greater the annual rainfall the greater the potential for water erosion and as the frequency of intense storms increases the greater the potential for water erosion. The contribution of soil to erosion relates to the size of the soil particles and the moisture content of the soil. Sandy and organic soils have...

## Depth of Water to Apply

Seasonal water demand and peak daily use vary considerably from crop to crop and from one field to the next. Deciding when to irrigate and how much water to apply are the two most difficult decisions to make in managing irrigation systems. Many different methods have been developed to help answer these two questions. The following discussion will explore some of the factors influencing these decisions and present one method for determining how much water to apply and the irrigation interval....

## Common Sources of Error

The accuracy of leveling can be greatly improved if several common errors are controlled 1. Instrument out of adjustment Anytime that the instrument is bumped or otherwise moved, it must be releveled. It is a good practice to check the leveling bubble both before and after reading the rod. Note resetting the level may change the instrument height. It must be checked, and if different or all or some, of the measurements will need to be repeated. 2. Rod not plumb The rod must always be held plumb...

## Handling Liquid Waste

Handling of liquid or slurry waste from buildings involves scraping or flushing the waste from where it is dropped by the animal to a pit or a storage tank. Once collected, the waste is treated and or disposed. Open feedlot waste is handled as runoff-carried waste, with natural precipitation carrying the liquid or the slurry, flowing from the pens into a drainage and collection system for subsequent removal or treatment and disposal. Liquid waste usually is handled by pumping, and is disposed...

## Compression Ratio

The compression ratio is the ratio of the total volume in a cylinder to the clearance volume. The clearance volume is the volume of the combustion chamber when the piston is at TDC, Figure 5.7. The total volume is the clearance volume plus the displacement. The compression ratio is an engine characteristic related to engine efficiency, that is, the ability of the engine to convert energy in the fuel to useful mechanical energy. The greater the compression ratio, the greater the potential...

## Insulation

Insulation is any material that reduces the rate of heat transfer by conduction. All building materials have some resistance to the movement of heat, but some, insulation, are more resistant than others. A common characteristic of insulation materials is low density (pounds cubic foot, kilogram cubic meter). Expanded polystyrene, which has a low density, has a higher thermal resistance than concrete, which has a very high density. Also, as the density of a material increases, for example, by...

## Psychometric Chart

A psychometric chart is a graphical representation of the seven physical properties of air. These physical properties are defined and described as follows 1. Dry-bulb temperature (dbt) The dry-bulb temperature is the temperature of air measured with a standard thermometer. Dry-bulb temperatures (and all other temperatures) usually are expressed in degrees Fahrenheit ( F) with customary units or degrees Celsius ( C) with SI units. 2. Wet-bulb temperature (wbt) The wet-bulb temperature is...

## Hydrologic Cycle

Climatological concerns involve more than the effects of pressure and air masses on the weather. The conservation of soil and water is based on an understanding of the hydrologic cycle. Figure 16.4 illustrates the movement of water in, on, and above the earth. The earth is a closed system in which all of the water circulates from one form to another. A study of the cycle can begin at any point, but we will start with precipitation. Precipitation is caused by the condensation of water vapor in...

## Calibrating Row Crop Planters

Row crop planters are used to plant crops in wider rows than those planted by grain drills. Row crop planters are commonly used to plant large seeds, such as corn, soybeans, and sunflowers, but are used for small seeded vegetable crops such as radishes. Row crop planters will have a speed hopper, a metering unit, a seed tube, a furrow opener and some type of closing or press wheels. Additional hoppers are sometimes used for fertilizer or insecticides, Figure 8.5. The common metering units for...

The over-current devices (fuses and circuit breakers) in the service entrance panel of a building are designed to protect the circuits from shorts and excessive current. The starting current of electric motors is greater than the operating current. In addition, when an electric motor is overloaded it will attempt to rotate until the electricity is disconnected or the lock-up torque is reached. Both of these situations can cause an excessive current in the motor circuit. The over current devices...

## Handling

Because of differences in shape, size, and consistency, each product must have a handling system capable of moving that specific product. The designer of a handling system also must consider product perishability and the desired form of the finished product. A harvester designed to harvest tomatoes for the fresh vegetable market will be different from one designed to harvest tomatoes used for catsup. Because of the prevalence of grains across the United States, they will be used to illustrate...

## Recurrence Interval

Another important aspect of rain is how often a storm of a specified intensity and duration may be expected to occur. The recurrence interval is defined as the number of years (on the average) before a storm of a given intensity and duration can be expected to recur. A storm that would be expected on an average of once in 25 years is said to have a 25-year recurrence interval, or is called a 25-year storm. It is important to remember that this is all based on the laws of probability, or chance,...

## Motor Nameplate Data

The National Electrical Manufacturers Association (NEMA) has developed a standardized system of identifying the important characteristics of motors. The standards do not specify a shape or location for the nameplate, and nameplates may not all contain the same information but the information that is important for motor selection will be included, see Figure 28.5. The following list of terms covers some of the information that can be found on motor nameplates Manufacturer The company name and...

## Power Transmission Through Power Trains

Power is transmitted through a power train. Study Figure 6.8 again. Can you predict how much power is available at either shaft A or shaft B The answer 50 horsepower is correct. If we assume no frictional losses in the power train, we will get out all of the power we put in. This can be demonstrated by using the horsepower equation to solve for the power available at shaft A.

## Complex Power Trains

Many machines use power trains that are more complex than what has been discussed up to this point. Figure 6.7 represents a power train designed to allow an engine or motor to supply the power for two different components. These components are attached to output shafts A and B. This figure illustrates the application of direction and speed of rotation for more complex power trains. Problem What are the speed and the direction of rotation of shaft A and shaft B in Figure 6.7 Solution In this...

## Surface

In surface irrigation, water is applied by allowing it to flow over the surface by gravity or through drip valves (a process called trickle or drip irrigation). The common gravity systems are flood and furrow. Flood systems require relatively flat land and the water is distributed in level borders or contoured levees. Land for furrow irrigation can have a small slope. For level borders and contoured levees, the water usually is delivered by surface ditch. Ditches can deliver water for furrows,...

## Units Cancellation

Some problems are more complex than the examples we have used, and many do not have patterns or previously developed equations. Equations can be developed for some of these problems, but an alternative approach is units cancellation. Problems of this type will usually involve several quantities. All of these quantities, except n, will have a unit such as feet, pounds, gallons, and so on. Units cancellation follows two mathematical principles (1) the units of measure associated with the numbers...

## Leveling Terms 1531 Bench Mark

A bench mark (BM) is an object whose elevation above mean sea level is known or assumed to be known. A bench mark must be an object that is dimensionally stable because it is the reference point for all of the elevations for a survey. If the bench mark elevation is accidentally changed, all surveys that used it must be redone. Bench marks allow a survey to be repeated at a later date and permit a surveyor to tie elevations from the current survey to elevations established in previous surveys. A...

## Company Name

The company name should be considered in machinery selection. Manufacturers spend years and multitudes of resources establishing a reputation. A company's reputation is based on the quality and durability of its products, service to its customers, or a combination of both. It is important to know if a manufacturer will stand behind its product and warranties. The importance of selecting tractors and machinery from reputable companies cannot be overstated. In some situations, the best economic...

## Areas of Standard Geometric Shapes

One of the most common applications of surveying is to measure the area of a lot, field, farm, or ranch. When a high level of accuracy is required, a professional engineer or a land surveyor should be employed. If this level of accuracy is not required, many areas can be determined with nothing more elaborate than a steel tape and the application of area formulas from geometry. The area of an irregularly shaped field can be found by subdividing it into standard shapes, determining the areas of...

## Two Stroke Cycle

Parts of a two-stroke cycle engine. FIGURE 5.3. Parts of a two-stroke cycle engine. The spark plug Ares, the piston reaches top dead center (TDC), burning occurs, and pressure builds rapidly in the cylinder. This is called the ignition and power event. As soon as the piston moves away from the head far enough to expose the exhaust port, the cycle begins again. If you count the movements of the piston, you will find that it has traveled two strokes or one revolution of the...

## Gear Sizes

It is common to use gears in power trains when the shafts are very close together, when a large amount of power is being transmitted or in transmissions where selectable speed ratios are needed. The sizes of gears are determined in the same way as those of chains and sprockets. The sprocket equation can be used without modification. In some situations when the speeds of the driver and driven shafts are known, pulley, sprocket, and gear sizes can be determined by using speed ratios instead of...

## Determining Areas of Irregular Shaped Fields Using Standard Geometric Shapes

Very few agricultural fields or lawns are standard geometric shapes. They may not be as complicated as the field illustrated in Figure 13.15, but the principles FIGURE 13.15. Example of determining the area of an irregular shape. FIGURE 13.15. Example of determining the area of an irregular shape. Determining Areas of Irregular-Shaped Fields Using Standard Geometric Shapes for determining areas are the same. The total area is the sum of each individual area. The key to efficient calculations is...

## Rounding Numbers

Rounding is used to eliminate figures that are not significant. When the digits to be rounded are to the left of the decimal point, the digits are replaced by zeros. For example, if you need to reduce the area of an acre, 43,560 ft2, to two significant digits, round to 44,000 ft2. When the digit being dropped is greater than 5, add one to the next digit remaining. When the digit being dropped is less than 5, the first remaining digit is unchanged. If the digit being dropped is exactly 5, leave...

## Calculating Voltage Drop

To maintain the heat produced by electricity passing through a resistance at the designed level, national standards, primarily the National Electric Code, limit the voltage drop allowed in a circuit. For most circuits this is 2 or 3 . Voltage drop is the term used to describe the reduction in voltage that occurs as electricity flows through a resistance. Voltage drop occurs because materials resist the flow of electricity the critical issue is to ensure it does not become excessive. The amount...

## Horsepower

Although power is a basic unit, in agriculture the more common unit is horsepower. Different measures of horsepower are used. For example, when discussing tractors, you may use engine horsepower, brake horsepower, drawbar horsepower, or power take-off horsepower. In the following section we will investigate the principles of horsepower. Horsepower is an arbitrary unit that was developed by James Watt to promote his early steam engines. He watched horses pulling loads of water out of mine shafts...

## Drawbar Power

Drawbar power (Dbhp) is power measured at the point implements are attached to the tractor, drawbar or 3 point hitch. During tractor testing a load cell is placed between the tractor and a load. The drawbar pull and the speed of travel are recorded and used to calculate drawbar power. Using measurements of pull (pounds) and speed (miles per hour) eliminates the PTO power equations. Because force is measured in pounds and velocity (V) measures both distance traveled and the time required to...

## Determining Areas of Irregular Shaped Fields Using Trapezoidal Equations

Occasionally it becomes necessary to determine the area of a field or other property that has one irregular-shaped boundary. This is a very common problem when one of the boundaries is formed by surface water. In this situation, the area can be determined by dividing the shape into a series of trapezoids and summing the individual areas. In situations where the trapezoids can be laid out so the heights are the same, the trapezoidal summation equation can be used. Problem What is the area...

## Screw

The screw is a modification of the inclined plane combined with a lever. The threads of a screw or a bolt are an inclined plane that has been rolled into the shape of a cylinder. A lever is used to turn the threads, which causes the load to move along the cylinder. An example of this principle is the screw type jack. Figure 4.16 illustrates this principle as it is used in a jack, where the jack handle is the force arm. The same principle applies to a bolt and nut. In the case of a FIGURE 4.16....

## Variable Costs

Variable costs are associated with the operation of a machine and occur only when the machine is used. The term operating costs frequently is used to describe variable costs. Variable costs are usually figured on an hourly basis, but they can be figured using acres, bales or any other appropriate unit. The common variable costs are 1. Repairs and maintenance (RM ) The costs of repair and maintenance are related to the type of machine, the purchase price and the hours of use. The repair and...

## Electric Motors

An electric motor is an energy conversion device like internal combustion engines, but instead of using the energy in a liquid fuel they use energy supplied by electricity. An electric motor requires an interaction between the rotating parts and the stationary parts. Two common types of interaction are conduction and induction. The principles of a conduction motor will be used to explain the function of electricity motors. Electricity flowing through a conductor induces an electrical magnetic...

## Principles of Calibration

In Chapter 1, two characteristic of mathematical problem where discussed. Both of these must be applied when calibrating dispensing machines. It would be a rare occurrence for a dispensing machine to distribute the desired amount of material. In this case perfection is not expected. Therefore levels of acceptability must be established. The amount of error that would be considered acceptable varies for each machine and situation. In some cases guidelines or standards have been established, but...

## Moisture Content

The moisture content scales are usually located on the right side of the chart. To locate a value for moisture, move horizontal to the right from the state point, Figure 23.3. A psychrometric chart from the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) or similar group will contain all of seven of these scales. Figure 23.4 is a low precision chart that can be used for learning about psychrometrics and solving the sample problems, but an ASHRAE chart should...

## Converting Tractor Power Ratings

Manufactures can use anyone of the four power ratings to advertise their tractors. When manufactures use engine or brake power to rate a tractor they are not providing any useful information because the useable power will be less than that. When the tractor is rated by engine or brake power, the PTO power will be less because of the losses in the power train. The drawbar power will be less because there are additional losses in the transmission and drive train and a tractor is not able to apply...

## Stationary Calibration

Both bulk and singulating row crop planters can be calibrated stationary by following the procedure used for stationary calibration of fertilizer applicators and grain drills. When the stationary method is used, the seeding rate is calculated by dividing the seeds planted per revolution of the drive wheel by the simulated acres covered per revolution of the drive wheel, when the stationary method is used or This equation can also be written as where R seeding rate (seeds ac) sd number of seeds...

## Mobile Calibration

Mobile calibration methods are the same for air seeders as for grain drills. One difference is the number of rows that must be collected. Air seeders are so large that it is not practical to collect all of the rows. Recommendations for the number of rows that should be collected vary, but 25 is a general recommendation. The appropriate number of seed hoses are disconnected from the individual seed tubes and connected to a bag or other collection device. The seeder is driven a fixed distance,...

## Areas of High and Low Pressure

Weather is greatly influenced by atmospheric pressure systems. High pressure and low pressure centers are indicators of the type of weather to be expected. Winds blow in a counterclockwise direction around a low pressure center and in a clockwise direction around a high pressure center. Closely spaced systems indicate a steep pressure gradient and high wind speeds when the systems are farther apart, the wind speeds are lower. A trough line may develop between two low pressure areas, and a...

## Calibrating Sprayers

Accurate calibration of spray equipment is very important because with only slight changes the application rate may cause chemical damage to the crop or the environment, be wasteful of materials, or be ineffective. There is one important difference between the design of fertilizer spreaders, grain drills, row crop planters and sprayers. The method used to control the flow rate of the material for a sprayer is not normally ground driven. The application rate (gal ac) is a function of the flow...

## Categories of Tractors

The diversity of modern agriculture requires many tractor designs. Historically, utility (use) has been the basis of tractor classification schemes. Based on utility, there are six categories of tractors general purpose, row crop, orchard, vineyard, industrial, and garden. The designers of modern tractors have attempted to produce tractors with the broadest possible uses, but these categories are still applicable if a sub-category is added for each type of propulsion system rear wheel drive...

## Calibrating Grain Drills

The traditional end wheel grain drill includes a hopper, a metering unit, seed tube and furrow opener for each row, and the metering unit drive train, Figure 8.4. Grain drills also use bulk or volume metering. The rows are usually spaced 6-10 inches (15-25 cm) apart. Combining the row spacing and number of metering units is the traditional method for indicating the width of the drill. A drill identified as 13-6 would have 13 metering units spaced 6 inches apart or a width of 18 x6 12 9 ft. The...

## Using Profile Data

The results of profile leveling surveys are most useful when they are plotted in a graph. The principal purposes for plotting a profile are (1) to aid in the selection of the most economical grade, location, and depth of irrigation canals, drainage ditches, drain tile lines, sewer lines, roads, etc. and (2) to determine the amount of cut or fill required for these installations. The graph is plotted with the elevation on the ordinate (vertical scale) and the stations on the abscissa (horizontal...

## Theory of Operation

The function of all internal combustion engines is to convert fuel (chemical energy) to power. This is accomplished by burning a fuel in a closed chamber and using the increase in temperature within the closed chamber to cause a rise in pressure. The pressure produces a force on the head of the piston causing it to move. The linear movement of the piston is converted to rotary motion (at the crankshaft), Figure 5.1. Rotary motion is more useful than linear movement. All internal combustion...

## Cropping and Management Factor CP

The original USLE separated the cropping factor (C) and management factor (P) into two different terms. In this discussion, they have been combined. The cropping factor is used to estimate the relative effectiveness of the practice to retard soil loss when compared to a continuously tilled field. The management factor (P) is an estimation of the effect of conservation practices in reducing soil loss. These factors combined are a function of the crop raised, the management practice, the planting...

## Taping

The most accurate traditional method of measuring distances uses a steel tape. When proper procedures are followed the error will be less than 1.0 ft in 3,000 ft. The standard equipment for a taping party, usually at least three people, consists of a tape, two range poles, a set of 11 chaining pins, two plumb bobs, a hand level, and a field notebook. Individual items of taping equipment are described in the following paragraphs. The traditional device for measuring distance accurately is the...