Fluid Power Systems for Electromech Prog 9th Term-Introduction

7/24/2019 Fluid Power Systems for Electromech Prog 9th Term-Introduction

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ALEXANDRIA UNIVERSITY

FACULTY OF ENGINEERING

Mechanical Engineering Department

Hydraulic Machines and Fluid Mechanics Branvh.

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9thTerm Electromechanical Program

FALL Term (Sept Dec 2012)

Fluid Power Systems

By

Dr. Ihab Gaber Ahmed Adam


Faculty of Engineering

Alexandria University


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Dr.Ihab G. Adam FALL 2012 9thTerm Elctomechanical Program.

Introduction-1

Hydraulic Power SystemsOutline:

1.

Introduction

2. Basic hydraulic system components and its hydraulic symbols

-

Pumps

- Actuators (Hydraulic cylinders and motors)

- Control Valves (Direction - Flow - Pressure)

3. Analysis (construction and operation) of some basic hydraulic circuits

4. Applications on Hydraulic Equipments circuits ( Loader,)

References:

1. Anthony Esposito, "Fluid Power with Applications."

2. F. N. Norvelle, "Fluid Power Technology."

3. Michael J. Pinches and John G. Ashby, "Power Hydraulics."

Fluid Systems

Fluid Transport Systems Fluid Power Systems

Fluid Poweris the technology that deals with generation, control and transmission of power using

pressurized fluids.

Fluid Power Systems

Fluid power system is a mechanism for converting mechanical power into hydraulic power (kinetic

and pressure) in a fluid, transmitting that power through a conduit, control it and then reconverting it

to mechanical power in order to perform work.


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Introduction-2

Fluid Power Systems

Hydraulic Power Systems Pneumatic Power Systems

use incompressible fluid (Liquids) use compressible fluid (gases)

- Water (freezes, evaporates, is poor Air

lubricant and rust metal components)

- Oil

Advantages of Fluid Power Systems:

1. High torques or forces from compact (small) size unit.

2. Stepless (infinitely) variable speeds and forces (or torques).

3. High accuracy of control.

4. Instantly reversible, eliminating the need to come to a gradual stop.

5. Self lubrication

6.

Fully adapted to electrical and electronic control.

7. Provide cushioning to reduce the mechanical effects of impact or shock loads.

Disadvantages of Fluid Power Systems:

1.

High pressure hazards.

2. Fire hazards.

3. Possible leakage of the fluid.

4. Component's wear due to contamination of the fluid.

Applications of Fluid Power SystemHydraulic systems are extremely important to the operation of heavy equipment. Basic hydraulic

principles are used when designing hydraulic implement systems, steering systems, brake systems

and power train systems. An understanding of the basic hydraulic principles must be accomplished

before continuing into machine systems.

1. Fluid power steers and breaks.

2. Machine tool industry.

3.

Food processing.

4. Drills teeth.

5.

Control airplanes (flaps, landing gear, and doors).

6. Cranes.

7. Lift truck.

8. Agricultural equipments.


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Introduction-3

Hydraulic Power System Components

1. Fluids (usually oil)

-To transmit power.

-To lubricate moving parts.

-To dissipate heat.

-To seals clearances between mating parts.

2. Tanks

-

To hold the fluid.-To allow fluid cooling.

-To allow foam (air bubble) separation.

3. Fluid Conditioning Device

-To keep the fluid clean (Filters)

-To Cool the fluid

4. Positive Displacement Pumps

-

The source of the hydraulic power-Convert the mechanical power to hydraulic power.

5. Prime mover

-Electrical motor, diesel engine and gasoline engine

-To drive the pump

6. Actuators

-Hydraulic cylinder for linear motion

-

Hydraulic motor for rotary motion

-

To perform work

7. Control Valves

-To control fluid flow rate (Flow Control Valve)

-To control fluid flow direction (Direction Control Valve)

-To control fluid flow pressure (Pressure Control Valve)

8. Conductors

-

Pipes or tubes - To carry the fluid


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Introduction-4

Mobile construction machines are designed using various hydraulic components (tanks,

fluids, pumps and motors, valves and cylinders). Some components when used in different parts of

the circuit perform different functions. Although these components may look alike, they may be

given different names. The ability to identify the component, state the components function and

describe the components operation will allow the serviceman to reduce complex circuits to several

simple circuits that may be more easily understood.

Hydraulic Jack


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Introduction-5

Pumps

Mechanical Power (T) Pump Hydraulic Power (PQ)

Non-Positive Displacement Pumps Positive Displacement Pumps

Hydrodynamic Pumps Hydrostatic Pumps

-

High flow rate (Q)

- Low Pressure (P)

-

Used in fluid transport

- Centrifugal Pump

- Propeller (axial) pump

- Smooth and continuos flow

- Qis inversely proportion to P

- No need for pressure relief valve

-

Low flow rate (Q)

- High Pressure (P)

-

Used in fluid power

- Gear Pump

- Vane Pump

- Piston Pump

- Relatively pulsating flow

- Qis almost constant60

NVQ

DT

- Pressure relief valve must be used to

protect the pump against over

pressure.

Pump's Hydraulic Symbols

Unidirectional Fixed displacement pump

Unidirectional Variable displacement pump

Bi-directional Fixed displacement pump

Bi-directional Variable displacement pump

Pumps do not pump pressure, but they produce fluid flowPressure is due to the elevation difference, friction resistance and/orLOADS


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Introduction-6

Si ng le su ct io n Do ub le s uc ti on

Multi stages

Centri fugal ( impel ler ) type Axial (propeller ) type

Non Positive disp lacement

External Internal

screw lobe

Gerotor

Gear pu mps

Unbalanced Balanced

vane pumps

Bent axis Sw ash plate

Axial Radial

piston pumps

Positive di splacement

Hydraulic Pumps


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Introduction-7

Positive Displacement Pumps

With this pump, a definite volume of liquid is delivered for each cycle of pump operation,

regardless of resistance, as long as the capacity of the power unit driving a pump is not exceeded. If

an outlet is completely closed, either the unit driving a pump will stall or something will break.

Therefore, a positive-displacement-type pump requires a pressure regulator or pressure-relief valve

in the system.

60

NVQ dTh

Th

Actual

Q

QVol

meVolTotal *

Positive Displacement Pump Performance curves


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-9


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Introduction-10

Hydraulic Actuators

Hydraulic Power Actuators Mechanical Power

Hydraulic Cylinders Hydraulic Motors

for Linear Motion for Rotary Motion

Linear Hydraulic Actuators (Hydraulic Cylinders)

Single Acting Hydraulic Cylinder

Single acting cylinder can exert a force in only one direction (extension or retraction). Single actingcylinders do not retract hydraulically; it retracts by gravity or spring.

Double Acting Hydraulic Cylinder


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-11


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in


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Introduction-13

Directional Control Valves

Two-Position Directional Control Valves

Four Way Valve

Manual-actuated, two-position, four-way, four

ports, spring-offset Directional Control Valve.

Mechanical-actuated, two-position, four-way, fourports, spring-offset Directional Control Valve.

Solenoid-actuated, two-position, four-way, four

ports, spring-offset Directional Control Valve.

Three-Position Directional Control Valves

Manual-actuated, three-position, four-way, four

ports, spring-centered Directional Control Valve.

Pilot-actuated, three-position, four-way, four


Solenoid-actuated, three-position, four-way, four



15/19

---- ----------------

_______

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Introduction-15

Pressure Control Valves (PCV)

Pressure Relief Valve

It is used as a safety device to prevent over pressurizing the system.

Pressure Reducing Valve

Pressure reducing valves are used when we need to operate one or more branches of afluid power circuit at pressures lower than the maximum system pressure.

Comparison of Pressure Relief Valve and Pressure Reducing Valve

Pressure Relief Valve Pressure Reducing Valve

1. Senses pressure upstream of

the valve.

2. Outlet port returns to tank.

3. Outlet flow at tank pressure

(usually near atmospheric).

4. Valve normally closed.

1. Senses pressure downstream of the

valve.

2. Outlet port attached to branch circuit.

3. Outlet flow at branch circuit pressure.

4. Valve normally open.


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-17

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D Ih b G Ad FALL 2012 9th T El h i l P

Introduction-18

Basic Hydraulic Circuits

Control of a single-acting cylinder Control of a double-acting cylinder

Regnerative circuit Drilling machine application

Double-pump hydraulic system Locked cylinder using pilot check valve

Fluid Power Systems for Electromech Prog 9th Term-Introduction

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