FLUID POWER SYSTEMSUNIT 1 FLUID POWER SYSTEMS AND FUNDAMENTALS .• WHAT IS HYDRAULIC SYSTEM? • Hydraulic system is the technology that deals with the generation. using pressurized liquid. and transmission of power. control. • The word hydraulics is derived from the Greek word HYDRO and means Water. safety. Constant force or torque(regardless of speed changes) 4.ADVANTAGES OF HYDRAULIC SYSTEM 1. Simplicity. Multiplication of force(without using cumbersome gears. economy(fewer moving parts compare to mechanical or electrical system) . Easy and accuracy of control(by the use of simple lever and push button) 2. pulleys and levers) 3. Long life cycle and low maintenance 7. . Easily automated 8. High force density and compact construction 6.5. Easy reversal movement. • Hydraulic oil always should be clean filtration is very critical . • Hydraulic lines can burst. possibly resulting in injuries to people. and leakage is impossible to eliminate completely. LIMITATIONS OF HYDRAULIC SYSTEM • Hydraulic lines are messy . • Most hydraulic oils can cause fires if an oil leak occurs in an area of hot equipment. . Valves to control oil direction. . A pump to force the oil through the system. 5. and flow rate. 2. Piping which carries the oil from one location to another. 4. An actuator to convert the pressure of the oil into mechanical force or torque to do useful work. COMPONENTS OF A HYDRAULIC SYSTEM 1. 3. An electric motor or other power source to drive the pump. pressure. 6. A tank (reservoir) to hold the hydraulic oil. Components of a simple hydraulic system 1 – pump 2 – oil tank 3 – flow control valve 4 – pressure relief valve 5 – hydraulic cylinder 6 – directional control valve 7 – throttle valve . Control submarines 5. Transportation 12. Coal mines 6. It jacks up an automobile (Hydraulic jack) 2.. Harvest crops 8. Drives high over head trams 3. Moves earth (Earth moving equipment like excavators.Presses 9. Machine tools 10. Construction . bull dozers.Launches space ship 4. Applications of hydraulic system 1. Material handling equipment 11.) 7. borewell drills etc. Stable viscosity characteristics. Adequate low-temperature properties 8. Good flammability characteristics 9. 2. Low volatility . Good lubricity 3. High bulk modulus and degree of incompressibility 7. Stable physical and chemical properties 5. Compatibility with system materials 4.Required Qualities of a Good Hydraulic Fluid 1. Good heat dissipation capability 6. Simple and easy handling 19. Low coefficient of expansion 18. Better fire resistance 12. Inexpensive. Good oxidation stability 15. Ready availability 20. Better rust and corrosion preventive qualities 16. . Good demulsibility 11. Nontoxicity 14.10. Low density and specific gravity 17. Lower foaming tendency 13. ” . PASCAL’S LAW Fluid power technology actually began in 1650 with the discovery of Pascal’s Law. Simply this law says that: “Pressure applied to a confined(static) fluid is transmitted undiminished in all directions throughout the fluid and acts perpendicular to the surfaces in contact with the fluid. Application of Pascal's law to simple hydraulic jack (Force multiplication) . . . Diagram B shows the pump stroking downward. HYDRAULIC JACK In this system (Figure 2-1). a reservoir and a system of valves has been added to Pascal's hydraulic lever to stroke a small cylinder or pump continuously and raise a large piston or an actuator a notch with each stroke. Diagram A shows an intake stroke.A. . MOTOR-REVERSING SYSTEM. if pressure rises too high. • A reversing valve directs fluid to either side of the motor and back to the reservoir. • Figure 2-2 shows a power-driven pump operating a reversible rotary motor. • A relief valve protects the system against excess pressure and can bypass pump output to the reservoir.B. . neutral position . OPEN-CENTER SYSTEM. •To operate several functions simultaneously.C. An open-center system is efficient on single functions but is limited with multiple functions. a control-valve spool must be open in the center to allow pump flow to pass through the valve and return to the reservoir. an open-center system must have the correct connections. • In this system. • In neutral. • Oil from a pump is routed to the three control valves in series. Return liquid from the cylinder is directed through the return line and on to the next valve. The return from the first valve is routed to the inlet of the second. the oil passes through the valves in series and returns to the reservoir. OPEN-CENTER SYSTEM. the incoming oil is diverted to the cylinder that the valve serves. • Figure 2-4 shows an open-center system with a series connection. and so on. as the arrows indicate. . This system is satisfactory as long as only one valve is operating at a time. C. • When a control valve is operated.
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