hydraulics & pneumatics

HYDRAULICS & PNEUMATICS

Presented by: Dr. Abootorabi

Actuators

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Hydraulic Cylinders

Actuators are the components used in a hydraulic system to

provide power to a required work location.

Cylinders are the hydraulic system components that convert

fluid pressure and flow into linear mechanical force and

movement.

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Hydraulic Cylinders

A basic cylinder consists of:

Piston

Piston rod

Barrel

The piston forms sealed, variable-volume chambers in

the cylinder.

System fluid forced into the chambers, drives the

piston and rod assembly.3

Hydraulic Cylinders

Seals prevent leakage between:

Piston and cylinder barrel

Piston rod and head

Barrel and its end pieces

Wiper seal, or scraper, prevents dirt and water from

entering the cylinder during rod retraction.

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Hydraulic Cylinders

Various seals are used in a cylinder

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Hydraulic CylindersVarious seals are used in a cylinder

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Hydraulic Cylinders

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Various seals are used in a cylinder

Hydraulic Cylinders

Cylinders are typically classified by operating principle:

Single-acting

Double-acting

Single-acting Double-acting 8

Hydraulic CylindersSingle-acting cylinder exert force either on extension or

retraction:

They require an outside force to complete the second

motion (either by a spring or by the weight load).

Double-acting cylinder generate force during both

extension and retraction:

Directional control valve alternately directs fluid to

opposite sides of the piston

Force output varies between extension and retraction

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Hydraulic CylindersSingle-acting cylinder

hydraulic ram (or plunger cylinder): piston and rod form one unit

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Hydraulic CylindersSingle-acting cylinder

Scissor lifting table:

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Hydraulic CylindersDouble-acting cylinder

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Hydraulic CylindersDouble-acting cylinder types:

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Hydraulic CylindersDouble-acting cylinder types:

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Hydraulic Cylinders

Effective piston area is reduced on retraction due to

the rod cross section.

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Hydraulic Cylinders

Telescoping cylinders are available for applications

requiring long extension distances:

Rod is made up of several tubes of varying size

nested inside of the barrel

Each tube extends, producing a rod longer than the

cylinder barrel

Typical example is the actuator that raises the box on

a dump truck

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Hydraulic Cylinders

Telescoping cylinders:

The maximum

force is at the

collapsed position

The speed will

increase at each

stage, but will not

allow much force

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Hydraulic CylindersCylinders often use hydraulic

cushions (to brake high stroke

speeds):

Provide a controlled

approach to the end of

the stroke

Reduces the shock of the

impact as the piston

contacts the cylinder

head

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Hydraulic Cylinders

Cushioning is not

required for speeds of

v<6 m/min.

This type of end position

cushioning is used for

stroke speed between 6

m/min and 20 m/min. At

higher speed, additional

cushioning or braking

devices must be used.

Cylinders with end position

cushioning:

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Hydraulic Cylinders

A variety of mounting configurations are used to attach the

cylinder body and rod end to machinery:

Fixed centerline

Fixed noncenterline

Pivoting centerline

Expected cylinder loading is the major factor in the

selection of the mounting style.

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Hydraulic Cylinders

Head-end (Fixed centerline) flange mount

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Hydraulic Cylinders

Fixed-noncenterline mount

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Hydraulic Cylinders

Pivoting-centerline, clevis mount

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Hydraulic Cylinders

Pivoting-centerline, trunnion mount

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Hydraulic Cylinders

Types of mounting:

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Hydraulic Cylinders

The force generated by a cylinder is calculated by multiplying

the effective area of the piston by the system pressure.

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F=p.A

By consideration of

mechanical efficiency:

Hydraulic CylindersCylinder characteristics

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Hydraulic Cylinders

Cylin

der

chara

cteri

stic

s

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dp: cylinder dia.

Ap: cylinder area

dST: piston rod

dia.

Hydraulic Cylinders

Speed at which the cylinder extends or retracts is

determined by:

Flow Rate (Q)

Effective Area (A)

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Q [m3/s] = A [m2] X [m/s]

Piston velocityEffective area

Hydraulic CylindersBuckling resistance

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Hydraulic CylindersSelecting a cylinder (Example)

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Hydraulic CylindersSelecting a cylinder (Example)

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Hydraulic CylindersSelecting a cylinder (Example)

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Buckling resistance diagram:

Reference: Festo Didactic Hydraulic

Hydraulic CylindersS

ele

cting

a cy

lind

er (E

xam

ple

)

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Hydraulic CylindersSelecting a cylinder (Example)

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Hydraulic CylindersSelecting a cylinder (Example)

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Hydraulic Cylinders

Hydraulic cylinder manufacturers provide detailed

specifications and basic factors such as:

Bore

Stroke

Pressure rating

Other details, such as service rating, rod end

configurations, and dimensions

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Hydraulic CylindersTypical manufacturer’s catalog page

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Bailey International Corporation

Limited-Rotation Hydraulic Actuators

Limited-rotation devices (swivel drive) are actuators with an

output shaft that typically applies torque through

approximately 360° of rotation.

Models are available that are limited to less than one

revolution, while others may produce several revolutions.

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Limited-Rotation Hydraulic Actuators

Most common designs of limited-rotation actuators are:

Rack-and-pinion

Vane

Helical piston and rod

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Limited-Rotation Hydraulic ActuatorsRack-and-pinion limited rotation actuator

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Here

maximum

angle may be

larger than

360°.

Limited-Rotation Hydraulic Actuators

Vane limited-rotation actuator

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Limited-Rotation Hydraulic Actuators

Helical piston and rod limited-rotation actuator

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Limited-Rotation Hydraulic ActuatorsLimited-rotation actuators are used to perform a

number of functions in a variety of industrial situations:

Indexing devices on machine tools

Clamping of workpieces

Operation of large valves

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Limited-rotation

actuators are used in this

robotic arm:

Hydraulic Motors

Hydraulic motors are called rotary actuators.

They convert fluid pressure and flow into torque and

rotational movement.

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Hydraulic MotorsSystem fluid enters the housing and applies pressure

to the rotating internal parts.

This, in turn, moves the power output shaft and applies

torque to rotate a load.

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Primary parts that produce the rotating motion in most

hydraulic motors are either:

Gears

Vanes

Pistons

Hydraulic Motors

The external gear hydraulic motor is the most common and

simplest of the basic motor types:

Unbalanced load on the bearings

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Hydraulic Motors

The most common internal gear motor has a gerotor design

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Hydraulic Motors

Basic vane motor (unbalanced)

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Hydraulic Motors

A basic, balanced vane motor

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Hydraulic Motors

Axial piston motors

are available in two

configurations:

Inline

Bent axis

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Hydraulic Motors

Inline piston motor

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Hydraulic Motors

Inline piston motor

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Hydraulic Motors

Bent-axis piston motor

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Hydraulic Motors

Radial piston motor

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Hydraulic Motors

Hydraulic motors may be incorporated into circuits using

series or parallel connections:

Series circuits: total system pressure is determined by

adding the loads placed on each unit

Parallel circuits: each motor receives full system

pressure; loads must be matched or equal flow supplied

to each motor if constant speed is desired from each unit

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Hydraulic Motors

Motors in series

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Hydraulic Motors

Motors in parallel

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Hydraulic Motors

Motors in parallel with flow control

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Hydraulic Motors

Hydraulic motor formulas:

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Power:

The end.

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