Chapter 3 Basic Physical Principles Applications to Fluid Power Sy S stems

Transcription

1 Chapter 3 Basic Physical Principles Applications to Fluid Power Systems 1

2 Objectives Identify and explain the design and operation of the six basic machines. Describe the factors that affect energy in fluid power systems. Explain how the potential power of a fluid power system is established. Describe the nature of heat and how it is measured in fluid power systems. Goodheart-Willcox Co., Inc. 3 Objectives Explain the nature of electricity and the basic methods used for electrical l measurement. 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 2

3 Simple Machines Millions of designs of complex machines exist in our society today. Goodheart-Willcox Co., Inc. 5 Brand X Simple Machines However, there are only six basic types of machines: Lever Inclined plane Wedge Screw Pulley Wheel and axle Goodheart-Willcox Co., Inc. 6 3

4 Simple Machines Levers First-class lever Goodheart-Willcox Co., Inc. 7 Simple Machines Levers Second-class lever Goodheart-Willcox Co., Inc. 8 4

5 Simple Machines Levers Third-class lever Goodheart-Willcox Co., Inc. 9 Simple Machines Inclined plane Wedge Photo courtesy of handiramp.com Goodheart-Willcox Co., Inc. 10 5

6 Simple Machines Screw Goodheart-Willcox Co., Inc. 11 Pulley Simple Machines Dynamic Graphics Goodheart-Willcox Co., Inc. 12 6

7 Wheel and axle Simple Machines Creatas Goodheart-Willcox Co., Inc. 13 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 7

8 Mechanical Measurements Torque is a turning or twisting force applied to a shaft hft Designated in pound-feet or pound-inches Work is the application of force through a distance Designated in foot-pounds or horsepower Goodheart-Willcox Co., Inc. 15 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 8

9 Mechanical Measurements Mechanical efficiency is a comparison of the work kinput and work output tof a machine Calculated by dividing the workput of the machine by the work input Expressed as a percentage Always less than 100% due to losses Goodheart-Willcox Co., Inc. 17 Principles of Heat Transfer Thermodynamics is the science dealing with the properties of matter related to heat and the 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 9

10 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 Principles of Heat Transfer Temperature is determined by the rate of molecular l movement within a substance 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

11 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 Principles of Heat Transfer Heat may be moved using three modes of transfer: Conduction Convection Radiation Goodheart-Willcox Co., Inc

12 Principles of Heat Transfer Conduction involves molecular activity in solids Goodheart-Willcox Co., Inc. 23 Principles of Heat Transfer Convection uses physical currents in gases or liquidsid Goodheart-Willcox Co., Inc

13 Principles of Heat Transfer Radiation transfers heat by the use of electromagnetic ti waves Goodheart-Willcox Co., Inc. 25 Electricity and Magnetism An atom is the smallest identifiable part of an element Composed of: Electrons ( ) Protons (+) Neutrons (no charge) Goodheart-Willcox Co., Inc

14 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 Electricity and Magnetism Magnetism is the ability of a material to attract iron Goodheart-Willcox Co., Inc

15 Electricity and Magnetism Electrical current can be used to magnetize iron and diron alloys Goodheart-Willcox Co., Inc. 29 Electricity and Magnetism Electricity may be produced using the lines of force that tsurround a magnet 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

16 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 slaw Amperage = Volts Ohms I = E R Goodheart-Willcox Co., Inc. 31 Electricity and Magnetism Two types of current flow are used in electrical circuits 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

17 Electricity and Magnetism Electrical circuits are made up of four basic elements Conductors Control devices Loading devices Electrical l energy source Electrical circuits may be connected using either a series or parallel format Goodheart-Willcox Co., Inc. 33 Electricity and Magnetism Series circuit places all of the loads on a single current tflow path Goodheart-Willcox Co., Inc

18 Electricity and Magnetism Parallel circuit provides an individual current flow path for each of the loads Goodheart-Willcox Co., Inc. 35 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

19 General Characteristics of Fluids Major difference between liquids and gases is compressibility Liquids act much like a solid Gases change volume when pressurized Goodheart-Willcox Co., Inc. 37 Basic Properties of Materials Specific weight is the weight of a specified volume of a substance at a given temperature 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

20 Pressure Measurements in Fluids Several pressure scales are used to indicate the pressure of a fluid Gauge pressure Absolute pressure Vacuum Head Atmosphere Goodheart-Willcox Co., Inc. 39 Pressure Measurements in Fluids Under normal atmospheric pressure: Gauge pressure scale reads 0 psi Absolute scale reads 14.7 psi Goodheart-Willcox Co., Inc

21 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 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

22 Fluid Reactions to Pressure and Temperature Ideal gas laws are used in many situations in pneumatic systems Approximate how real gases react to pressure, temperature, and volume changes Boyle s law for constant temperature Charles law for constant pressure Gay-Lussac s law for constant volume General gas law combines all three Goodheart-Willcox Co., Inc. 43 Review Question Examine the descriptions below and then identify the basic machine: 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

23 Review Question Energy in motion is known as energy. kinetic Goodheart-Willcox Co., Inc. 45 Review Question The distance traveled in a standard basic unit of time, such as 3 per second, dis known as. velocity Goodheart-Willcox Co., Inc

24 Review Question Name four ways in which heat is generated in a fluid power system. A) Resistance to fluid flow in pipes and hoses, B) flow over relief valves, C) flow through h flow control valves, and D) internal leakage of pumps and motor. Goodheart-Willcox Co., Inc. 47 Review Question The two factors that control the amount of electricity it produced dby electromagnetic ti induction are and. A) The rate of movement of the conductor or the magnetic field and B) the number of magnetic lines of force cut. Goodheart-Willcox Co., Inc

25 Review Question Name the four basic elements of a basic electrical lcircuit. it A) Electrical conductors, B) control devices, C) loading devices, and D) source of electrical lenergy. Goodheart-Willcox Co., Inc. 49 Review Question The basic concept of law is that pressure applied to a confined, nonflowing fluid is transmitted equally to all points in the fluid. Pascal s Goodheart-Willcox Co., Inc

26 Glossary Absolute pressure A pressure scale where the zero point represents 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 Glossary Atmosphere 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

27 Glossary Conduction A basic term relating to the transfer of heat or electricity through a material. Goodheart-Willcox Co., Inc. 53 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 that causes it to accelerate (move). Goodheart-Willcox Co., Inc

28 Glossary General gas law A general equation that t expresses the relationships between pressure, volume, and temperature when applied to a gas (P1 V1 T1 = P2 V2 T2). Head The height of a column of water or other liquid necessary to develop a stated pressure. Goodheart-Willcox Co., Inc. 55 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 a substance without changing temperature during a change of state. Goodheart-Willcox Co., Inc

29 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 phenomena produced by the magnetic lines of force surrounding natural or electromagnets. Goodheart-Willcox Co., Inc. 57 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 yprovides multiple paths for the current or fluid to follow as it moves through a circuit. Goodheart-Willcox Co., Inc

30 Glossary Pascal s law A basic scientific law that t states t pressure applied to 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. Goodheart-Willcox Co., Inc. 59 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

31 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 or twisting force applied to a shaft. Goodheart-Willcox Co., Inc. 61 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

32 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