Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
1/28/2010 Chapter 3 Basic Physical Principles Applications to Fluid Power Systems y 1 1/28/2010 Objectives Identify and explain the design and operation of th six the i basic b i machines. hi Describe the factors that affect energy in fluid power systems. Explain how the potential power of a fluid power system is established established. Describe the nature of heat and how it is measured in fluid power systems. © Goodheart-Willcox Co., Inc. 3 Permission granted to reproduce for educational use only. Objectives Explain the nature of electricity and the basic methods th d usedd for f electrical l t i l measurement. t Identify and explain the operation of basic electrical circuits. Name and describe the characteristics associated with the fluids used in fluid power systems. © Goodheart-Willcox Co., Inc. 4 Permission granted to reproduce for educational use only. 2 1/28/2010 Simple Machines Millions of designs of complex machines exist i our society in i t today. t d Brand X © Goodheart-Willcox Co., Inc. 5 Permission granted to reproduce for educational use only. Simple Machines However, there are only six basic types of machines: hi – – – – – – Lever Inclined plane Wedge Screw Pulley Wheel and axle © Goodheart-Willcox Co., Inc. 6 Permission granted to reproduce for educational use only. 3 1/28/2010 Simple Machines Levers – First-class lever © Goodheart-Willcox Co., Inc. 7 Permission granted to reproduce for educational use only. Simple Machines Levers – Second-class lever © Goodheart-Willcox Co., Inc. 8 Permission granted to reproduce for educational use only. 4 1/28/2010 Simple Machines Levers – Third-class lever © Goodheart-Willcox Co., Inc. 9 Permission granted to reproduce for educational use only. Simple Machines Inclined plane Wedge Photo courtesy of handiramp.com © Goodheart-Willcox Co., Inc. 10 Permission granted to reproduce for educational use only. 5 1/28/2010 Simple Machines Screw © Goodheart-Willcox Co., Inc. 11 Permission granted to reproduce for educational use only. Simple Machines Pulley Dynamic Graphics © Goodheart-Willcox Co., Inc. 12 Permission granted to reproduce for educational use only. 6 1/28/2010 Simple Machines Wheel and axle Creatas © Goodheart-Willcox Co., Inc. 13 Permission granted to reproduce for educational use only. Basic Principles of Mechanics Energy is the capacity to do work – Potential energy is stored energy – Kinetic energy which is energy in motion Force is the overall effort needed to produce, change, or stop motion Pressure is force exerted over a unit area © Goodheart-Willcox Co., Inc. 14 Permission granted to reproduce for educational use only. 7 1/28/2010 Mechanical Measurements Torque is a turning or twisting force applied to a shaft h ft – Designated in pound-feet or pound-inches Work is the application of force through a distance – Designated in foot foot-pounds pounds or horsepower © Goodheart-Willcox Co., Inc. 15 Permission granted to reproduce for educational use only. Mechanical Measurements Power is the rate at which work is performed – Designated in foot-pounds per minute Mechanical advantage is a relationship between the effort put into a machine and the resistance overcome – Calculated using either the forces or distances involved – Expressed as a numeric ratio © Goodheart-Willcox Co., Inc. 16 Permission granted to reproduce for educational use only. 8 1/28/2010 Mechanical Measurements Mechanical efficiency is a comparison of the workk input i t andd workk output t t off a machine hi – Calculated by dividing the workput of the machine by the work input – Expressed as a percentage – Always y less than 100% due to losses © Goodheart-Willcox Co., Inc. 17 Permission granted to reproduce for educational use only. Principles of Heat Transfer Thermodynamics is the science dealing with the properties ti off matter tt related l t d to t heat h t andd the th conversion of energy from one form to another Heat is kinetic energy – Measured in British thermal units (Btu) or calories © Goodheart-Willcox Co., Inc. 18 Permission granted to reproduce for educational use only. 9 1/28/2010 Principles of Heat Transfer Heat is generated in a fluid power system whenever a pressure drop occurs that does not produce work © Goodheart-Willcox Co., Inc. 19 Permission granted to reproduce for educational use only. Principles of Heat Transfer Temperature is determined by the rate of molecular l l movementt within ithi a substance bt Temperature is measured in degrees – Fahrenheit scale (United States) – Celsius scale (everywhere else) – Rankine and Kelvin scales (often used for scientific and engineering calculations) © Goodheart-Willcox Co., Inc. 20 Permission granted to reproduce for educational use only. 10 1/28/2010 Principles of Heat Transfer Sensible heat can be measured by a thermometer – Felt as “hot” or “cold” Latent heat is the heat needed to change the state of a substance without changing its temperature – Ice to water – Water to steam © Goodheart-Willcox Co., Inc. 21 Permission granted to reproduce for educational use only. Principles of Heat Transfer Heat may be moved using three modes of t transfer: f – Conduction – Convection – Radiation © Goodheart-Willcox Co., Inc. 22 Permission granted to reproduce for educational use only. 11 1/28/2010 Principles of Heat Transfer Conduction involves molecular activity in solids lid © Goodheart-Willcox Co., Inc. 23 Permission granted to reproduce for educational use only. Principles of Heat Transfer Convection uses physical currents in gases or li id liquids © Goodheart-Willcox Co., Inc. 24 Permission granted to reproduce for educational use only. 12 1/28/2010 Principles of Heat Transfer Radiation transfers heat by the use of electromagnetic l t ti waves © Goodheart-Willcox Co., Inc. 25 Permission granted to reproduce for educational use only. Electricity and Magnetism An atom is the smallest identifiable part of an element l t Composed of: – Electrons (–) – Protons (+) – Neutrons (no charge) © Goodheart-Willcox Co., Inc. 26 Permission granted to reproduce for educational use only. 13 1/28/2010 Electricity and Magnetism Electrical flow occurs when electrons leave the outer orbital paths and move other free electrons through the substance with them © Goodheart-Willcox Co., Inc. 27 Permission granted to reproduce for educational use only. Electricity and Magnetism Magnetism is the ability of a material to attract iron © Goodheart-Willcox Co., Inc. 28 Permission granted to reproduce for educational use only. 14 1/28/2010 Electricity and Magnetism Electrical current can be used to magnetize iron andd iron i alloys ll © Goodheart-Willcox Co., Inc. 29 Permission granted to reproduce for educational use only. Electricity and Magnetism Electricity may be produced using the lines of f force th thatt surroundd a magnett – When an electrical conductor cuts these magnetic lines of force, electricity is produced – Electrical output is dependent on the number of lines cut and the speed with which they are cut – This is called electromagnetic induction © Goodheart-Willcox Co., Inc. 30 Permission granted to reproduce for educational use only. 15 1/28/2010 Electricity and Magnetism Electricity flowing in a conductor involves: – Electrical current (amperage) – Potential (voltage) – Resistance (ohms) The relationship between these elements is stated in Ohm Ohm’ss law Amperage = Volts Ohms I=ER © Goodheart-Willcox Co., Inc. 31 Permission granted to reproduce for educational use only. Electricity and Magnetism Two types of current flow are used in electrical circuits i it – Direct current (dc) • Electrons flow in one direction only – Alternating current (ac) • Electrons flow first in one direction, stop, and then reverse their direction of flow © Goodheart-Willcox Co., Inc. 32 Permission granted to reproduce for educational use only. 16 1/28/2010 Electricity and Magnetism Electrical circuits are made up of four basic elements – – – – Conductors Control devices Loading devices El t i l energy source Electrical Electrical circuits may be connected using either a series or parallel format © Goodheart-Willcox Co., Inc. 33 Permission granted to reproduce for educational use only. Electricity and Magnetism Series circuit places all of the loads on a single currentt flow fl path th © Goodheart-Willcox Co., Inc. 34 Permission granted to reproduce for educational use only. 17 1/28/2010 Electricity and Magnetism Parallel circuit provides an individual current fl path flow th for f eachh off the th loads l d © Goodheart-Willcox Co., Inc. 35 Permission granted to reproduce for educational use only. General Characteristics of Fluids Liquids and gases are both considered fluids – Each substance is able to flow – Each adjusts its shape to fit the container in which it is held © Goodheart-Willcox Co., Inc. 36 Permission granted to reproduce for educational use only. 18 1/28/2010 General Characteristics of Fluids Major difference between liquids and gases is compressibility ibilit – Liquids act much like a solid – Gases change volume when pressurized © Goodheart-Willcox Co., Inc. 37 Permission granted to reproduce for educational use only. Basic Properties of Materials Specific weight is the weight of a specified volume l off a substance bt att a given i temperature t t and pressure Specific gravity is a comparison of the weight of a substance to the weight of an equal volume of water © Goodheart-Willcox Co., Inc. 38 Permission granted to reproduce for educational use only. 19 1/28/2010 Pressure Measurements in Fluids Several pressure scales are used to indicate the pressure off a fl fluid id – – – – – Gauge pressure Absolute pressure Vacuum Head Atmosphere © Goodheart-Willcox Co., Inc. 39 Permission granted to reproduce for educational use only. Pressure Measurements in Fluids Under normal atmospheric pressure: – Gauge pressure scale reads 0 psi – Absolute scale reads 14.7 psi © Goodheart-Willcox Co., Inc. 40 Permission granted to reproduce for educational use only. 20 1/28/2010 Fluid Reactions to Pressure and Temperature Pascal’s law is a key principle related to the operation of a fluid power system – States that pressure applied to a confined nonflowing fluid is transmitted undiminished to all points in the fluid © Goodheart-Willcox Co., Inc. 41 Permission granted to reproduce for educational use only. Fluid Reactions to Pressure and Temperature Bernoulli’s theorem states the total energy in a volume of flowing fluid is the same at every point in its path of flow © Goodheart-Willcox Co., Inc. 42 Permission granted to reproduce for educational use only. 21 1/28/2010 Fluid Reactions to Pressure and Temperature Ideal gas laws are used in many situations in pneumatic ti systems t – Approximate how real gases react to pressure, temperature, and volume changes – Boyle’s law for constant temperature – Charles’ law for constant p pressure – Gay-Lussac’s law for constant volume – General gas law combines all three © Goodheart-Willcox Co., Inc. 43 Permission granted to reproduce for educational use only. Review Question Examine the descriptions below and then id tif the identify th basic b i machine: hi A. Two inclined planes fastened together. B. A spiral inclined plane. C. A circular form of a lever. A. Wedge. B. Screw C. Wheel and axle © Goodheart-Willcox Co., Inc. 44 Permission granted to reproduce for educational use only. 22 1/28/2010 Review Question Energy in motion is known as _____ energy. kinetic © Goodheart-Willcox Co., Inc. 45 Permission granted to reproduce for educational use only. Review Question The distance traveled in a standard basic unit of time, i suchh as 3 per second, d iis known k as _____. velocity © Goodheart-Willcox Co., Inc. 46 Permission granted to reproduce for educational use only. 23 1/28/2010 Review Question Name four ways in which heat is generated in a fl id power system. fluid t A) Resistance to fluid flow in pipes and hoses, B) flow over relief valves, C) flow fl through h h flow fl controll valves, l and D) internal leakage of pumps and motor. © Goodheart-Willcox Co., Inc. 47 Permission granted to reproduce for educational use only. Review Question The two factors that control the amount of electricity l t i it produced d d by b electromagnetic l t ti induction are _____ and _____. A) The rate of movement of the conductor or the th magnetic ti field fi ld andd B) the th number b off magnetic lines of force cut. © Goodheart-Willcox Co., Inc. 48 Permission granted to reproduce for educational use only. 24 1/28/2010 Review Question Name the four basic elements of a basic electrical l t i l circuit. i it A) Electrical conductors, B) control devices, C) loading devices, and D) source of electrical l i l energy. © Goodheart-Willcox Co., Inc. 49 Permission granted to reproduce for educational use only. Review Question The basic concept of _____ law is that pressure applied li d to t a confined, fi d nonflowing fl i fluid fl id is i transmitted equally to all points in the fluid. Pascal’s © Goodheart-Willcox Co., Inc. 50 Permission granted to reproduce for educational use only. 25 1/28/2010 Glossary Absolute pressure – A pressure scale l where h the th zero point i t represents t a perfect vacuum. Alternating current – Electrical current that reverses direction on a regular cycle due to a change in voltage polarity. The common international standards are 50 or 60 cycles per second (or hertz). © Goodheart-Willcox Co., Inc. 51 Permission granted to reproduce for educational use only. Glossary Atmosphere –1 1. The pressure created by a column of gas extending between space and the surface of Earth at sea level. – 2. A pressure of 14.7 psia. © Goodheart-Willcox Co., Inc. 52 Permission granted to reproduce for educational use only. 26 1/28/2010 Glossary Conduction – A basic term relating to the transfer of heat or electricity through a material. © Goodheart-Willcox Co., Inc. 53 Permission granted to reproduce for educational use only. Glossary Electron – One of the three basic parts of an atom. These negatively-charged portions of the atom orbit the nucleus containing neutrons and protons. Force – An influence on a body y that causes it to accelerate (move). © Goodheart-Willcox Co., Inc. 54 Permission granted to reproduce for educational use only. 27 1/28/2010 Glossary General gas law – A generall equation ti that th t expresses the th relationships l ti hi between pressure, volume, and temperature when applied to a gas (P1V1T1 = P2V2T2). Head – The height of a column of water or other liquid necessary to develop a stated pressure. pressure © Goodheart-Willcox Co., Inc. 55 Permission granted to reproduce for educational use only. Glossary Horsepower – A standard unit of power equal to 550 foot-pounds of work per second or 33,000 foot-pounds per minute. Latent heat – The amount of heat absorbed or released by ya substance without changing temperature during a change of state. © Goodheart-Willcox Co., Inc. 56 Permission granted to reproduce for educational use only. 28 1/28/2010 Glossary Lever – One of the simple machines. Consists of a rigid bar pivoted about a fulcrum. Used to multiply a force or movement. Magnetism – The pphenomena produced p byy the magnetic g lines of force surrounding natural or electromagnets. © Goodheart-Willcox Co., Inc. 57 Permission granted to reproduce for educational use only. Glossary Mechanical advantage – The ratio of the force produced by a machine to the applied input force. Parallel circuit – An electrical or fluid power circuit that simultaneously y provides p multiple p paths p for the current or fluid to follow as it moves through a circuit. © Goodheart-Willcox Co., Inc. 58 Permission granted to reproduce for educational use only. 29 1/28/2010 Glossary Pascal’s law – A bbasic i scientific i tifi law l that th t states t t pressure applied li d to t a confined, nonflowing fluid is transmitted undiminished to all points in the fluid. Pressure – Force per unit area, which is usually expressed in pounds per square inch (psi) or bar. bar © Goodheart-Willcox Co., Inc. 59 Permission granted to reproduce for educational use only. Glossary Sensible heat – Heat that can be measured with a thermometer and will result in a feeling of warming or cooling as heat is applied or removed from a substance. Does not change the state of a substance. Specific gravity – The ratio of the weight of a given volume of a material to the weight of an equal volume of water at 4° Celsius. © Goodheart-Willcox Co., Inc. 60 Permission granted to reproduce for educational use only. 30 1/28/2010 Glossary Thermodynamics – A science dealing with the relationships between the properties of matter affected by temperature and the conversion of energy from one form to another. Torque – The turning g or twisting g force applied pp to a shaft. © Goodheart-Willcox Co., Inc. 61 Permission granted to reproduce for educational use only. Glossary Vacuum – A space in which the pressure is below normal atmospheric pressure. The concept applies to a variety of fluid power component and circuit applications, such as the intake lines of both hydraulic pumps and pneumatic compressors. © Goodheart-Willcox Co., Inc. 62 Permission granted to reproduce for educational use only. 31 1/28/2010 Glossary Wheel and axle – One of the simple machines, consisting of a wheel attached to an axle. The common center of the wheel and axle is the fulcrum, allowing the device to act as a second or third class lever depending where the effort is applied. © Goodheart-Willcox Co., Inc. 63 Permission granted to reproduce for educational use only. 32