hydraulic power. hydraulic power hydraulics vs. pneumatics early hydraulic uses hydrodynamic systems...
TRANSCRIPT
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
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
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 500 - 5000 psi• Generally produce more power
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
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
Hydrodynamic Systems
• Fluid is in motion
• Force and energy are transmitted by flow
Water Turbine Propeller
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Hydrostatic Systems
• Fluid does not flow quickly or continuously
• Fluid is pressurized
• Force and energy transmitted by pressure
• Most common in industrial
settings
Hydrostatic Systems
Click the arrows to activate the hydraulic press.
Pascal’s Law Pressure exerted by a confined fluid acts undiminished equally in all directions
FA
p
Liquid FlowFlow 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
vQ ( A)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
Liquid Flow Example
Float
Q = 15 gal/mind = 2 in. v = ?
Convert 15 gal/min to in.3 /min
1 gal = 231 in.3
Reprinted with permission from Introduction to Fluid Power, by James L. Johnson. Copyright © 2002 Thomson Delmar Learning.
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?
315gal 231in.min 1gal
3465 gal 3in.
1min gal
3in.3500
min
v3
2in.3465 ( 3.14in. )
mSub/Solve
in
Liquid Flow ExampleA 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?
vin.
1,1Fin 0al 0min
2A 3.14F nal in.i
2Sub/Solve A ( 1 )
2Formula A r vFormula Q ( A)
Q = 3465 in.3/min d = 2 in. v = ?
v
3in.3465
2
in.min
3.14 in.
Mechanical Advantage
out
in
FMA
F
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Force at the outputMechanical Advantage
Force at the input
Mechanical Advantage ExampleA 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?
din = 4.0 in.
dout = 12.0 in.
Fin = 100. lbfFin = 100. lbf Fout = ?
din = 4.0 in. dout = 12.0 in.
Ain = ? Aout = ?
p = ? MA = ?
Mechanical Advantage Example
Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in.
Ain=? Aout=? p=? MA=?
Find the area of each cylinder.
2inA 13F nal in.i
2inSub A ( 2.0/Sove inl )
2Formula A r
2outA 110F nal in.i
2outSub A ( 6.0/Sove inl )
2Formula A r
Mechanical Advantage Example
Fin=100. lb Fout=? Rin=2.0 in. Rout=6.00 in.
Ain=12.57 in.2 Aout=113.10 in.2 p=? MA=?
Find the pressure in the system.
p2
lb8.Final 0
in.
p2
100. lb
12Sub /S
.57olv
in.e
pFormulaFA
Mechanical Advantage Example
2
2out
lb in.F 9.0 10
2in.
Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in.
Ain=12.57 in.2 Aout=113.10 in.2 p=7.955 lb/in.2 MA=?
Find the force that the output cylinder can lift.
2outF 9Fina 0l . 10 lb
out2 2
Flb7.955
in. 113Sub /Solv
.10 in.e
pFormulaFA
2out 2
lbF 7.955 ( 113.10in. )
in.
Mechanical Advantage Example
Fin=100. lb Fout=900.28 lb Rin=2.0 in. Rout =6.00 in.
Ain=12.57 in.2 Aout=113.10 in.2 p=7.96 lb/in.2 MA=?
Find the mechanical advantage of the system.
Final MA 9
900.28 lb
MASub/Solve100 lb
out
in
FMAFormul
Fa
Conservation of Energy: An increase in velocity results in a decrease in pressure. Likewise, a decrease in velocity results in an increase in pressure.
Bernoulli’s Principle
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
Common Hydraulic System Components
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Cylinder
Transmission Lines
Directional Control Valve
Pump
Reservoir
Filter
Click the lever on the valve to extend and retract the cylinder.
Common Hydraulic System Components
Reservoir Pump
Cylinder
Valve
Image Resources
National Fluid Power Association. (2008). What is fluid power. Retrieved February 15, 2008, from http://www.nfpa.com/OurIndustry/OurInd_AboutFP_WhatIsFluidPower.asp
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 http://office.microsoft.com/en-us/clipart/default.aspx