1. Hydraulic Power

2. Hydraulic Power Hydraulic power Hydraulics vs. pneumatics
Early hydraulic uses
Hydrodynamic systems
Hydrostatic systems
Liquid flow
Mechanical advantage
Bernoulli's principle
Viscosity
Common hydraulic system components
Emerging hydraulic application example

3. Hydraulic Power Hydraulics
The use of a liquid flowing under pressure to transmit power from one location to another
Liquid in a hydraulic system behaves like a solid since it compresses very little
Oil is most often used in hydraulic systems, although other systems also may use synthetic oils or water.

4. Hydraulic Power
At least two examples of hydraulic power are visible on the fire truck.

5. Hydraulics vs. Pneumatics
Hydraulic Systems . . .
Use a relatively incompressible liquid
Have a slower, smoother motion
Are generally more precise
Lubricate naturally
Are not as clean as pneumatics when leakage occurs
Often operate at pressures of psi
Generally produce more power
The slower, smoother motion of hydraulics is what makes hydraulic systems more precise than pneumatic systems.

6. Early Hydraulic Uses Water Wheels Create rotational motion
Descriptions exist as early as 1st century BC
Several examples in ancient China
Grist mill is pictured
Modern turbines in hydro-powered dams are a sophisticated version of the water wheel used to create electricity.

7. Early Hydraulic Uses Roman Aqueducts
Delivered water to buildings, to agricultural fields, and to fountains
Used gravity to create flow
Fountains were decorative and used by people to collect water for practical use

8. Water Turbine Propeller
Hydrodynamic Systems
Fluid is in motion
Force and energy are transmitted by flow
Water Turbine Propeller
Pneumatic systems can also be referred to as hydrodynamic. Windmills are an example of such a system.
The early hydraulic examples in this presentation are hydrodynamic systems.
The picture is of a turbine that could be used to produce electricity.

9. Hydrostatic Systems Fluid does not flow quickly or continuously
Fluid is pressurized
Force and energy transmitted by pressure
Most common in industrial
settings
National Fluid Power Association & Fluid Power Distributors Association
Pneumatic systems can also be referred to as hydrostatic since such systems are often pressurized.

10. Hydrostatic Systems
Pascal’s Law Pressure exerted by a confined fluid acts undiminished equally in all directions
Click the arrows to activate the hydraulic press.

11. Liquid Flow
Flow Rate
The volume of fluid that moves through a system in a given period of time
Flow Velocity
The distance the fluid travels through a system in a given period of time
Symbol
Definition
Example Units Q
Flow Rate
gpm or gal/min
(gallons per minute)
in.3 / min v
Flow Velocity
fps or ft/s
(feet per second)
in. / min A
Area
in.2
fps = feet per second
fpm = feet per minute
gpm = gallons per minutes

12. Liquid Flow Example Q = 15 gal/min d = 2 in. v = ?
A flow meter attached to the main line in a hydraulic system measures the flow rate at 15 gpm. The line has an inside diameter of 2 in. What is the flow velocity in the meter?
Q = 15 gal/min
d = 2 in.
v = ?
Convert 15 gal/min to in.3 /min
1 gal = 231 in.3
Float
Many types of flow meters can be used to measure flow rate. The image in this slide is a variable flow meter. The float is lifted by gravity, so this type of meter is placed in a vertical line system.
Reprinted with permission from Introduction to Fluid Power, by James L. Johnson. Copyright © 2002 Thomson Delmar Learning.

13. Liquid Flow Example Q = 3465 in.3/min d = 2 in. v = ?
A flow meter attached to the main line in a hydraulic system measures the flow rate at 15 gpm. The line has an inside diameter of 2 in. What is the flow velocity in the meter?
Q = 3465 in.3/min d = 2 in. v = ?

14. Mechanical Advantage
The following formula solves for ideal mechanical advantage. Actual mechanical advantage is always less than the ideal calculation.
National Fluid Power Association & Fluid Power Distributors Association

15. Mechanical Advantage Example
A force of 100. lbf is applied to the input cylinder of the hydraulic press seen below. What is the pressure in the system? How much force can the output cylinder lift? What is the mechanical advantage of the system?
Fin = 100. lbf
Fin = 100. lbf Fout = ?
din = 4.0 in dout = 12.0 in.
Ain = ? Aout = ?
p = ? MA = ?
din = 4.0 in.
dout = 12.0 in.

16. Mechanical Advantage Example
Find the area of each cylinder.
Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in.
Ain=? Aout=? p=? MA=?

17. Mechanical Advantage Example
Find the pressure in the system.
Fin=100. lb Fout=? Rin=2.0 in. Rout=6.00 in.
Ain=12.57 in Aout= in p=? MA=?

18. Mechanical Advantage Example
Find the force that the output cylinder can lift.
Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in.
Ain=12.57 in.2 Aout= in p=7.955 lb/in MA=?

19. Mechanical Advantage Example
Find the mechanical advantage of the system.
Fin=100. lb Fout= lb Rin=2.0 in. Rout =6.00 in.
Ain=12.57 in.2 Aout= in p=7.96 lb/in MA=?

20. Bernoulli’s Principle
Conservation of Energy: An increase in velocity results in a decrease in pressure. Likewise, a decrease in velocity results in an increase in pressure.
This example portrays a venturi which is represented by a decrease in diameter. At the narrowed point, speed increases and pressure decreases.
This is important in hydraulic systems because the size of conduit or piping in a system will likely vary and impact the system based on this principle.
Bernoulli’s Principle also applies to pneumatic power, but it is a more important consideration for hydraulic power.

21. Viscosity The measure of a fluid’s thickness or resistance to flow
Crucial for lubricating a system
Measured in slugs/sec-ft (US) or centistokes (metric)
Hydraulic oil is usually around 1.4 slugs/sec-ft
Decreases as temperature increases
Absolute pressure is used to complete pneumatic calculations.

22. Common Hydraulic System Components
Cylinder
Directional Control Valve
Transmission Lines
Filter
Pump
Reservoir: The tank that holds fluid in a hydraulic system.
Transmission lines: Used to transport fluid in a circuit.
Pump: Used to create flow in the system.
Cylinder: Also called an actuator. Used to convert fluid power to linear mechanical power.
Filter: Used to remove contamination from fluids. Filters are also often next to lubricators. Lubrication helps prevent wear on the components in the system.
Directional control valve: Used to control which path a fluid takes in a circuit.
All systems also require seals and gaskets between components to reduce leakage in the system.
Reservoir
National Fluid Power Association & Fluid Power Distributors Association

23. Common Hydraulic System Components
Click the lever on the valve to extend and retract the cylinder.
Cylinder
Valve
Reservoir
Pump

24. Image Resources
National Fluid Power Association. (2008). What is fluid power. Retrieved February 15, 2008, from
Johnson, J.L. (2002). Introduction to fluid power. United States: Thomson Learning, Inc.
National Fluid Power Association & Fluid Power Distributors Association. (n.d.). Fluid power: The active partner in motion control technology. [Brochure]. Milwaukee, WI: Author.
Microsoft, Inc. (2008). Clip Art. Retrieved January 10, 2008, from