HYDRAULICS & PNEUMATICS

HYDRAULICS & PNEUMATICS

Presented by: Dr. Abootorabi

Actuators

1

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.

2

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.

4

Hydraulic Cylinders

Various seals are used in a cylinder

5

Hydraulic CylindersVarious seals are used in a cylinder

6

Hydraulic Cylinders

7

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

9

Hydraulic CylindersSingle-acting cylinder

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

10

Hydraulic CylindersSingle-acting cylinder

Scissor lifting table:

11

Hydraulic CylindersDouble-acting cylinder

12

Hydraulic CylindersDouble-acting cylinder types:

13

Hydraulic CylindersDouble-acting cylinder types:

14

Hydraulic Cylinders

Effective piston area is reduced on retraction due to

the rod cross section.

15

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

16

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

17

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

18

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:

19

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.

20

Hydraulic Cylinders

Head-end (Fixed centerline) flange mount

21

Hydraulic Cylinders

Fixed-noncenterline mount

22

Hydraulic Cylinders

Pivoting-centerline, clevis mount

23

Hydraulic Cylinders

Pivoting-centerline, trunnion mount

24

Hydraulic Cylinders

Types of mounting:

25

Hydraulic Cylinders

The force generated by a cylinder is calculated by multiplying

the effective area of the piston by the system pressure.

26

F=p.A

By consideration of

mechanical efficiency:

Hydraulic CylindersCylinder characteristics

27

Hydraulic Cylinders

Cylin

der

chara

cteri

stic

s

28

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)

29

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

Piston velocityEffective area

Hydraulic CylindersBuckling resistance

30

Hydraulic CylindersSelecting a cylinder (Example)

31


32


33

Buckling resistance diagram:

Reference: Festo Didactic Hydraulic

Hydraulic CylindersS

ele

cting

a cy

lind

er (E

xam

ple

)

34


35


36

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

37

Hydraulic CylindersTypical manufacturer’s catalog page

38

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.

39


Most common designs of limited-rotation actuators are:

Rack-and-pinion

Vane

Helical piston and rod

40

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

41

Here

maximum

angle may be

larger than

360°.


Vane limited-rotation actuator

42


Helical piston and rod limited-rotation actuator

43

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

44

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.

45

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.

46

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

47

Hydraulic Motors

The most common internal gear motor has a gerotor design

48

Hydraulic Motors

Basic vane motor (unbalanced)

49

Hydraulic Motors

A basic, balanced vane motor

50

Hydraulic Motors

Axial piston motors

are available in two

configurations:

Inline

Bent axis

51

Hydraulic Motors

Inline piston motor

52

Hydraulic Motors

Inline piston motor

53

Hydraulic Motors

Bent-axis piston motor

54

Hydraulic Motors

Radial piston motor

55

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

56

Hydraulic Motors

Motors in series

57

Hydraulic Motors

Motors in parallel

58

Hydraulic Motors

Motors in parallel with flow control

59

Hydraulic Motors

Hydraulic motor formulas:

60

Power:

The end.

61

Documents

HYDRAULICS & PNEUMATICS