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

Hydraulic and Pneumatic Systems 2

Hydraulic cylindersHydraulic cylinder

Hidraulikus munkahengerekRögzítőpálcás kivitel 1.

Hydraulic and Pneumatic Systems 3

Hydraulic cylinders

Hydraulic cylinder Hidraulikus munkahengerekHengeres kivitel 1.

Hengeres építési móddal készült hidraulika henger

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.

Hydraulic and Pneumatic Systems 5

Hydraulic cylindersCalculation of cylinders

1maxmaxFFFF FLc FLC FFF

maxmax

22110 pApAFC

1122 pApAFCB

10 A

Qv

2A

QvB

friction forces inertial forcesmaximum loadslow motion, can be often neglected

Backward:

Outward:

Q

A2A1

p1

p2vB

v0

Hydraulic and Pneumatic Systems 6

Hydraulic cylindersCalculation 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-slip2. Transition3. Normal behaviour

22112211 ApAp

F

QpQp

Fv LLc

92,085,0max

c

ηc

Δp

outwardsinwards at higher pressures

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

kL

64

4d

Maximum permissible force:

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.

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 actuator

Limited angle rotary actuator

Parallel piston rotary

actuator

??? ???

Hydraulic and Pneumatic Systems 10

Big pictures

End of normal presentationBeginning of big pictures

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)

Hydraulic and Pneumatic Systems 12

Hydraulic cylinders

Cylinder types: piston, single acting, pressing-cylinder

Spring

inside outside

Hydraulic and Pneumatic Systems 13

Hydraulic cylinders

Cylinder types: piston, single acting, puller

Spring

inside outside

Hydraulic and Pneumatic Systems 14

Hydraulic cylinders

Cylinder types: piston, double acting

Velocity is different

Hydraulic and Pneumatic Systems 15

Hydraulic cylinders

Cylinder types: piston, double acting

Piston rod on both side

Velocity is the same in both directions

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

Hydraulic and Pneumatic Systems 17

Hydraulic cylinders

Cylinder types: double acting piston, tandem

Hydraulic and Pneumatic Systems 18

Hydraulic cylinders

Cylinder types: single acting, fast moving

Hydraulic and Pneumatic Systems 19

Hydraulic cylinders

Cylinder types: double acting, fast moving

Hydraulic and Pneumatic Systems 20

Hydraulic cylinders

Cylinder types: telescopic, single acting

Large working paths or limited space

Hydraulic and Pneumatic Systems 21

Hydraulic cylinders

Cylinder types: telescopic, double acting

Large working paths or limited space

Hydraulic and Pneumatic Systems 22

Hydraulic cylindersChecking 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

Hydraulic and Pneumatic Systems 23

Hydraulic cylindersCushioning 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

Hydraulic and Pneumatic Systems 24

Rotary hydraulic actuators

Parallel piston rotary actuator

Hydraulic and Pneumatic Systems 25

Rotary hydraulic actuators

Hydraulic and Pneumatic Systems 26

Rotary hydraulic actuators

Rack-and-pinion piston-type rotary actuator:

Hydraulic and Pneumatic Systems 27

Rotary hydraulic actuatorsLimited angle rotary actuator:

Hydraulic and Pneumatic Systems 28

Rotary hydraulic actuatorsLimited angle rotary actuator:

Hydraulic and Pneumatic Systems 29

Rotary hydraulic actuators

Helix actuator: