2005/2006 I. Hydraulic and Pneumatic Systems 1

Hydraulic actuators: cylindersCylinder types:

Single acting:

work can be done only in one direction

Piston

Double acting piston:

Piston rod on both sides

Plunger

Work is done in both

directions

Telescopic Telescopic Fast moving

Tandem

Fast moving

2005/2006 I. Hydraulic and Pneumatic Systems 2

Hydraulic cylinders

Hydraulic cylinderHidraulikus munkahengerek

Rögzítőpálcás kivitel 1.

Rögzítőpálcás hidraulika henger, a hengerfejen található karimás rögzítéssel

2005/2006 I. Hydraulic and Pneumatic Systems 3

Hydraulic cylinders

Hydraulic cylinder Hidraulikus munkahengerek

Hengeres kivitel 1.

Hengeres építési móddal készült hidraulika henger

2005/2006 I. Hydraulic and Pneumatic Systems 4

Hydraulic cylinders

Properties:

The cylinders have to be good quality steel with close tolerances.

There have to be good sealing both at the piston rod and at the

cylinder.

With time dirt may come in and damage the surfaces. This has to be

possibly reduced.

In this case, the leakage will increase all the time.

2005/2006 I. Hydraulic and Pneumatic Systems 5

Hydraulic cylinders

Calculation of cylinders

1maxmaxFFFF FLc ++= FLC FFF +≈

maxmax

22110 pApAFC −=

1122 pApAFCB −=

1

0A

Qv =

2A

Qv

B=

friction forces inertial forcesmaximum loadslow motion, can

be often neglected

Backward:

Outward:

Q

A2A1

p1

p2vB

v0

2005/2006 I. Hydraulic and Pneumatic Systems 6

Hydraulic cylinders

Calculation of cylinders

Hydraulic cylinders should be possibly

operated in the 3rd region for smooth

operation.

If the cylinder is new, the leakage losses are

negligibly small so that:

ηc = ηmech

Ff1

v

2 3

1. Stick-slip

2. Transition

3. Normal behaviour

22112211ApAp

F

QpQp

Fv LLc −

=−⋅

=η

92,085,0max

−=cη

ηc

∆p

outwardsinwards

at higher pressures

2005/2006 I. Hydraulic and Pneumatic Systems 7

Hydraulic cylinders

Checking for buckling

n: safety factor: 1-3,5

lk: buckling length

I1: moment of inertia of the piston rod

E: elasticity modulus of the rod material

1

2

max

1IE

lnF

k

L ⋅⋅

=

π

64

4πd

Maximum permissible force:

2005/2006 I. Hydraulic and Pneumatic Systems 8

Hydraulic cylinders

Cushioning of cylinders:

A hard impact of the piston at the end surfaces has to be inhibited

– kinetic energy has to be absorbed.

This is done by increasing the hydraulic resistance at the end of

the stroke.

2005/2006 I. Hydraulic and Pneumatic Systems 9

Rotary hydraulic actuators

Swivel vane rotary actuator:

Limited angle in both directions

Maximum angle always smaller than 360°

The same torque in both directions

Piston rotary actuator:

With rack and gear coupling

Here maximum angle may be larger than 360°Mindkét irányban azonosan

működő hengerrel és fogasléces

meghajtással működtetett

tolódugattyús lengőhajtás

Párhuzamdugattyús

lengőhajtás

Forgódugattyús

lengőhajtás menettel

működtetett meghajtócsappal

Limited angle rotary

actuatorLimited angle rotary

actuator

Parallel

piston rotary

actuator

??? ???

2005/2006 I. Hydraulic and Pneumatic Systems 10

Big pictures

End of normal presentation

Beginning of big pictures

2005/2006 I. Hydraulic and Pneumatic Systems 11

Hydraulic cylinders

Cylinder types: plunger

smaller force, better efficiency, axial support is necessary

but cylinder does not have to be so good quality

Without inner buffer With inner buffer (pilot piston)

2005/2006 I. Hydraulic and Pneumatic Systems 12

Hydraulic cylinders

Cylinder types: piston, single acting, pressing-cylinder

Spring

inside outside

2005/2006 I. Hydraulic and Pneumatic Systems 13

Hydraulic cylinders

Cylinder types: piston, single acting, puller

Spring

inside outside

2005/2006 I. Hydraulic and Pneumatic Systems 14

Hydraulic cylinders

Cylinder types: piston, double acting

Velocity is different

2005/2006 I. Hydraulic and Pneumatic Systems 15

Hydraulic cylinders

Cylinder types: piston, double acting

Piston rod on both side

Velocity is the same in both directions

2005/2006 I. Hydraulic and Pneumatic Systems 16

Hydraulic cylinders

Cylinder types: piston, double acting

Piston rod on both side

Velocity is different in the two directions depending on

cross section ratio of the rods

2005/2006 I. Hydraulic and Pneumatic Systems 17

Hydraulic cylinders

Cylinder types: double acting piston, tandem

2005/2006 I. Hydraulic and Pneumatic Systems 18

Hydraulic cylinders

Cylinder types: single acting, fast moving

2005/2006 I. Hydraulic and Pneumatic Systems 19

Hydraulic cylinders

Cylinder types: double acting, fast moving

2005/2006 I. Hydraulic and Pneumatic Systems 20

Hydraulic cylinders

Cylinder types: telescopic, single acting

Large working paths

or limited space

2005/2006 I. Hydraulic and Pneumatic Systems 21

Hydraulic cylinders

Cylinder types: telescopic, double acting

Large working paths

or limited space

2005/2006 I. Hydraulic and Pneumatic Systems 22

Hydraulic cylinders

Checking for buckling:

Euler’s

cases

Picture

Free buckling length

Manner of end fixing

Note

1. Case

One end freeOne end fixed

Or trunnion at end

mounting style mounting style mounting style

2. Case

Two ends pivoted and guided

3. Case

One end guided and pivoted, other end

fixed

4. Case

Two ends fixed and guided

mounting style

2005/2006 I. Hydraulic and Pneumatic Systems 23

Hydraulic cylinders

Cushioning of cylinders:

1. Piston

2. Cushion nose

3. Cylinder cap

4. Stroke volume

5. Cushion orifice

6. Throttle

7. Cushion adjustment screw

8. Mother

9. Non-return valve

10. Gas valve

2005/2006 I. Hydraulic and Pneumatic Systems 24

Rotary hydraulic actuators

Parallel piston rotary

actuator

2005/2006 I. Hydraulic and Pneumatic Systems 25

Rotary hydraulic actuators

???

2005/2006 I. Hydraulic and Pneumatic Systems 26

Rotary hydraulic actuators

Rack-and-pinion piston-type rotary actuator:

2005/2006 I. Hydraulic and Pneumatic Systems 27

Rotary hydraulic actuatorsLimited angle rotary actuator:

2005/2006 I. Hydraulic and Pneumatic Systems 28

Rotary hydraulic actuators

Limited angle rotary actuator:

2005/2006 I. Hydraulic and Pneumatic Systems 29

Rotary hydraulic actuators

Helix actuator: