Fluid Power Hydraulics Chapter 1 PDF

‫السالم عليكم ورحمة هللا وبركاته‬ ‫‪1‬‬ Design of Hydraulic Control Circuits Assoc Prof. Magdy Raouf Marzouk Dr. Mohamed Hanafy Aly Faculty of engineering-Mattaria Mechanical Power Engineering Department...

‫السالم عليكم ورحمة هللا وبركاته‬ ‫‪1‬‬ Design of Hydraulic Control Circuits Assoc Prof. Magdy Raouf Marzouk Dr. Mohamed Hanafy Aly Faculty of engineering-Mattaria Mechanical Power Engineering Department 2  References Anthony Esposito; “Fluid Power with Applications” 2009, 7th edition, Pearson Prentice Hall. M. Galal, “Fluid Power Engineering”, 2009, McGraw Hill. M. J. Pinches, John G. Ashby; “Power Hydraulics” 1988, Prentice Hall International (UK) Ltd. 3  Course contents Hydraulic control Introduction to Hydraulic Power Systems Hydraulic Oils and Theoretical Background Pumps Hydraulic Control Valves Pressure-Control Valves Directional Control Valves Check Valves Flow Control Valves Actuators Accessories Hydraulic Accumulators Hydraulic Filters Hydraulic Pressure Switches Hydraulic circuit design 4  Learning Objective Explain what fluid power is Differentiate between the two terms hydraulics and pneumatics. Understand the difference between fluid power and fluid transport systems. Discuss the advantage and disadvantage of fluid power. Describe key applications of fluid power Specify the basic Components of fluid power systems 5  What is Fluid Power? Fluid power is the technology that deals with the generation, control, and transmission of power, using pressurized fluids. Fluid power is called hydraulics when the fluid is a liquid and is called pneumatics when the fluid is a gas. Thus fluid power is the general term used for both hydraulics and pneumatics. So we can say that hydraulics is the technology that deals with the generation, control, and transmission of power, using pressurized liquids. 6 Fluid Power is Everywhere 7 8 J:\private\oman\picture\SAM_3588.JPG 9 2. Applications of Hydraulics The place held by hydraulics in (modern) automation technology illustrates the wide range of applications for which it can be used. A basic distinction is made between: stationary hydraulics and mobile hydraulics Mobile hydraulic systems move on wheels or tracks while stationary hydraulic systems remain firmly fixed in one position. The following application areas are important for stationary hydraulics: Production and assembly machines of all types Presses Injection molding machines 10 Typical application fields for mobile hydraulics include: Automobiles, tractors, airplanes, submarines, missiles, boats. Construction machinery Excavators, elevating platforms Lifting and conveying devices Agricultural machinery Examples Excavators. The figure shows an excavator whose hydraulically actuated bucket digs soil from the ground and drops the soil into a dump truck at a construction site. The maximum lifting capacity is 18 ton. 11 Industrial hydraulic lift truck The figure shows a 3 ton capacity industrial hydraulic lift truck in the process of lifting a large stack of lumber in a warehouse. Power steering system Because the steering unit is fully fluid-linked, mechanical linkages, universal joints, bearings, reduction gears, and so forth, are eliminated. This provides a simple, compact system. In addition, very little input torque is required to produce the steering control needed. 12 Why Fluid Power High power power per weight much higher than density electric motors High Fluid power systems can move at high bandwidth speeds Because oil is stiff, enables precision Precise control motion Power can be Flexible hoses enables power to be piped snaked around corners and across joints 13 Advantages of Hydraulics Ease and accuracy of control. By the use of simple levers and push buttons, the operator of a hydraulic system can readily start, stop, speed up or slow down, and position forces that provide any desired horsepower with tolerances as precise as one ten-thousandth of an inch. Transmission of large forces using small components, i.e. great power-per-weight ratio. A hydraulic system (without using heavy gears, pulleys, and levers) can multiply forces simply and efficiently from a few grams to several hundred tons of output. 14  Simplicity, safety, economy. In general, fluid power systems use fewer moving parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, compactness, and reliability. Constant force or torque over velocity. Hydraulic systems are capable of providing constant force or torque regardless of speed changes. This is accomplished whether the work output moves a few centimeters per hour, several meters per minute, a few revolutions per hour, or thousands of revolutions per minute. Even movements independent of load. This is because liquids are considered relatively incompressible fluids. 15 16 Other advantages include, Start-up under heavy load. Instantly reversible motion. Automatic protection against overloads. Infinitely variable speed control. Drawbacks of Hydraulics In spite of all the previously mentioned advantages of hydraulic power system, it also have some drawbacks. For example, 1. Hydraulic components must be properly designed and installed to prevent oil leakage from the hydraulic system into the surroundings (danger of fire or accidents). 2. Hydraulic pipeline can burst due to excessive oil pressure if proper system design is not implemented. 3. Sensitivity to dirt. 4. Temperature dependence (change in viscosity). 5. Unfavorable efficiency factor. 17 The Classification of Power Systems Power systems are used to transmit and control power. This function is illustrated by Figure below. The following are the basic parts of a power system. The function of a power system. Source of energy, delivering mechanical power of rotary motion. Electric motors and internal combustion engines (ICE) are the most commonly used power sources. For special applications, steam turbines, gas turbines, or hydraulic turbines are used. Energy transmission, transformation, and control elements. Load requiring mechanical power of either rotary or linear motion. 18 The classification of power systems. 19 An automotive drive train. 20 Electrical Power Systems Electrical power systems solve the problems of power transmission distance and flexibility, and improve controllability. Figure below illustrates the principal of operation of electrical power systems. These systems offer advantages such as high flexibility and a very long power transmission distance, but they produce mainly rotary motion. Rectilinear motion, of high power, can be obtained by converting the rotary motion into rectilinear motion by using a suitable gear system Power transmission in an electrical power system. 21 Pneumatic Power Systems Pneumatic systems are power systems using compressed air as a working medium for the power transmission. The air compressor converts the mechanical energy of the prime mover into mainly pressure energy of compressed air. An air preparation process is needed to prepare the compressed air for use. The compressed air is stored in the compressed air reservoirs and transmitted through rigid and/or flexible lines. The pneumatic power is controlled by means of a set of pressure, flow, and directional control valves. Then, it is converted to the required mechanical power by means of pneumatic cylinders and motors (expanders). Figure below illustrates the process of power transmission in pneumatic systems. Power transmission in a pneumatic power system. 22 Hydrostatic Power Systems In the hydrostatic power systems, the power is transmitted by increasing mainly the pressure energy of liquid. These systems are widely used in industry, mobile equipment, aircrafts, ship control and others. This text deals with the hydrostatic power systems, which are commonly called hydraulic power systems. Figure below shows the operation principle of such systems. Power transmission in a hydraulic power system. 23 Comparison of Power Systems 24 Basic Hydraulic Power Systems Hydraulic system circuit, schematic, and symbolic drawings. 25