1. Understanding Principles of 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 and Disadvantages
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

5. Hydraulic System Components

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

7. Pascal’s Law Pressure applied to a confined fluid is:
10-lb
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
10 psi
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. Cycle Time
Fluid from pump
Fluid to reservoir
Fluid to reservoir
Fluid from pump
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, 1714 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 D t (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