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

Hydraulic Power

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

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

Hydrodynamic Systems

Fluid is in motion

Fluid is not pressurized

Force / energy is created by flow

Water Turbine Propeller

National Fluid Power Association & Fluid Power Distributors Association

Hydrostatic Systems

Fluid is at rest

Fluid is pressurized

Pressure creates force and energy

Most common in industrial settings

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

National Fluid Power Association & Fluid Power Distributors Association

Force at the outputMechanical Advantage

Force at the input

Mechanical Advantage ExampleA force of 100. lb 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. lbFin = 100. lb 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=7.955 lb/in.2 MA=?

Find the mechanical advantage of the system.

MAFinal 9.0

900.28 lb

MASub/Solve100. lb

out

in

FMAFormul

Fa

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/ft 3 (US) or centistokes (metric)

– Hydraulic oil is usually around 1.4 slugs/ft 3

Decreases as temperature increases

Common Hydraulic System Components

National Fluid Power Association & Fluid Power Distributors Association

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

Emerging Hydraulic Application Example

Hydraulic Hybrid VehiclesBraking provides stored energy that is used to propel the vehicle

forward.

UPS™ expects 60-70% better fuel economy and 40% reduction in CO2 emissions.

UPS