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Understanding Principles of Fluid Power Transmission

Understanding Principles of Fluid Power Transmission. Objectives. Define “hydraulics.” Describe the advantages and disadvantages of hydraulics as a method of power transmission. Describe basic hydraulic system components and functions. Explain Pascal’s Law and its relation to hydraulics.

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Understanding Principles of Fluid Power Transmission

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  1. Understanding Principlesof Fluid Power Transmission

  2. Objectives • Define “hydraulics.” • Describe the advantages and disadvantages of hydraulics as a method of power transmission. • Describe basic hydraulic system components and functions. • Explain Pascal’s Law and its relation to hydraulics. • Describe the relationship between force, pressure and area in a hydraulic system. • Explain how Conservation of Energy applies to a hydraulic system. • Calculate the “cycle time” for a hydraulic application. • Determine the mechanical and fluid horsepower output of a hydraulic system.

  3. Hydraulics • Science and technology dealing with the mechanical properties and practical applications of liquids in motion. • Hydrodynamics – Use fluid at high flow, low pressure. • Hydrostatics – Use fluids at high pressure, low flow.

  4. Advantages: Increased design flexibility. Infinitely variable speed. Reduced component wear. Easy reversibility. Multiplication of force. Disadvantages: Use of fluids at high pressure: Safety hazards Need for cleanliness Expense Advantages and Disadvantages

  5. Hydraulic System Components

  6. Basic Hydraulic System Operation Pump Pressure Relief Valve Cylinder Directional Control Valve Reservoir

  7. 10-lb 10 psi Pascal’s Law • Pressure applied to a confined fluid is: • transmitted undiminished in all directions, • acts with equal force on equal areas, and • acts at a right angle to the walls of the container. 1 in2 Area = 10 in2 Force = 100-lbs.

  8. F,P, A Relationships F(lbs.) A (in2) P(psi)

  9. Force, Pressure, Area Relationships in a Hydraulic System 100-lbs 1000-lbs 10-in2. 100 in2 10 psi Determine force (lbs.) and pressure (psi) in this system.

  10. Fluid to reservoir Fluid from pump Fluid to reservoir Fluid from pump Cycle Time • Total time required for hydraulic cylinder to complete one cycle. • Extend • Retract • Depends on volume (cylinder size) and flow (pump GPM).

  11. Fluid Horsepower • Fhp = P x Q • Where, • P = Pressure (psi) • Q = Flow rate (gpm) • 1714 = a constant 1714 A tractor has a hydraulic system with a maximum working pressure of 2500 psi and a flow rate of 11.5 gpm. What is the maximum fluid horsepower output?

  12. Mechanical vs. Fluid Power • Mechanical HP • Force (lbs) • Distance (ft.) • Time (min.) • Horsepower = • F x Dt (min) x 33,000 • Fluid HP • Pressure (psi) • Flow (GPM) • Horsepower = • Pressure x Flow 1714

  13. Mechanical vs. Fluid HP Example • Determine the Fluid HP and the Mechanical HP in the situation described: • 4.0-in. diameter ram • 24-in stroke • 50,000 lb load • 10-gpm pump

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