Hydraulic Actuators and Motors

1. Hydraulic Actuators and
Motors

2. Introduction
 Hydraulic cylinders and hydraulic motors perform a function opposite to
that performed by a pump. They extract energy from a fluid, and convert
it to mechanical energy to perform useful work.
Hydraulic
Cylinder
Electric
Motor
T x ωV x I
Hydraulic
Pump
P x Q
Hydraulic
Motor
F x v
T x ω
Hydraulic System

3. Introduction
 Hydraulic cylinders, also called linear actuators provide a force that drives
an external load along a straight line.
 Hydraulic motors, also called rotary actuators, provide a torque that drives
an external load along a circular path.
Hydraulic
Cylinder
Electric
Motor
T x ωV x I
Hydraulic
Pump
P x Q
Hydraulic
Motor
F x v
T x ω
Hydraulic System

5. Actuators :
•Actuators are those components of a fluid power system, which
produces mechanical work output.
•They develop force and displacement, which is required to
perform any specific task. The task may be of any kind, to move,
to press, to lift, to clamp.
•Actuators are common for both hydraulic and pneumatic system.
•Hydraulic actuators are made stronger to with stand pressure of
oil and develop huge amount of force.

6. •Speed of actuator depends on rate of working fluid. Rate of
flow of working fluid can be controlled using Flow Control
Valve (FCV).
•Force developed by cylinder is the product of pressure of
working fluid and the piston area.
•Force of actuator is controlled by controlling the pressure of
working fluid using Pressure Control Valve (PCV).
•Direction of motion of actuator is controlled by controlling the
direction of flow of fluid, by using Direction Control Valve
(DCV).

7. Telescopic
Boom Forklift
Airplane Wing Flaps
and Landing Gear

8. Telescopic
Boom Forklift

9. Airplane Wing Flaps
and Landing Gear

10. Actuators :
•Actuators are of two types:
–Linear actuator
–Rotary actuator
•Linear actuator
–Rotating cylinder
–Non rotating cylinder
•Single acting cylinder
•Double acting cylinder
–Special type cylinder
•Diaphragm cylinder
•Tandem cylinder
•Double rod end cylinder
•Telescopic cylinder
•Cylinder with cushioning

11. Rotary actuator
–Limited rotation actuators
•Vane type
•Piston type
–Continuous rotation actuators
•Based on direction
–Uni-directional motors
–Bi-directional motors
•Based on construction
–Gear type
–Vane type
–Piston type

12. Single Acting Hydraulic Cylinders
Graphic Symbol
(P&ID Symbol)
Push Action
Oil to extend Return by External Force
(e.g. Gravity)
Port
Extension
Retraction
PistonPiston Seal Rod
Barrel

13. Single Acting Hydraulic Cylinders
Push Action
Oil to extend, Spring for return
Pull Action
Oil to retract, Spring to extend

14. Double Acting Hydraulic
Cylinders
Graphic Symbol
(P&ID Symbol)
Oil to extend.
Oil for Return
Extension
Retraction
PistonPiston Seal
Rod
Seal
Rod
Barrel
Port BPort A

15. Double Ended Piston Rod
Double Acting Cylinder
Graphic Symbol
(P&ID Symbol)
Oil to extend.
Oil for Return
PistonPiston Seal
Rod Seal
Rod
Barrel
Port BPort A
Rod Seal

16. Cylinder Construction
Tie Rod Front CapBarrel
End Cap
Threaded Rod

17. Double Acting Hydraulic Cylinders

18. Single acting cylinder :

19. Double acting cylinder :

20. Special type Cylinder :
Diaphragm cylinder :

21. Tandem cylinder :

22. Double Rod End cylinder :

23. Telescopic Cylinder :
Symbol

25. Cylinder with Cushioning :

26. Cylinder Mounting Methods
Front Flange
Foot Bracket
Intermediate Trunnion
Rear Flange
Side Lug
Clevis (Rear Pivot)

27. Cylinder Mounting Methods
Direct Rear
Foot Bracket
Front Flange Clevis (Rear Pivot)
Intermediate TrunnionScrewed Front

28. Combining Cylinders with Mechanical Linkages:
Oscillatory motion with thrust amplification or reduction
First Class Lever Second Class Lever Third Class Lever
The three combinations are inverted slider crank mechanisms

29. Cylinder Alignment: Universal Joints
 A universal joint alignment accessory may be used. It allows fifteen degrees of
angular misalignment on each side of center. It also provides more load
carrying capabilities.
 It is recommended that not more than a thirty degree maximum misalignment
angle be used on the pins

30. Cylinder Force, Velocity and Power
 Extension Stroke
 Retraction Stroke
inextext
binext
bext
QpvFP
AQv
ApF



Piston Rod
Port Port
 
 
inretret
rbinret
rbret
QpFvP
AAQv
AApF



bA
rA

31. Cylinder Loading Through 1st class lever
   
 
 loadloadload
cylcylcyl
loadloadcylcyl
O
LF
LF
LFLF
M



sinsincoscos
sinsincoscos
0coscos
0
2
1
21




 As the lever rotates an angle ϴ from its initial orientation, the cylinder
rotates an angle фcyl and the load rotates with an angle фload
Neglecting friction and dynamic loading (small values compared to
forces from the cylinder thrust and load), then taking the moments
around the pivot, O, we have
L1 L2
ϕcyl
ϴ
O
Fload
Fcyl
ϕload
load
cyl
load
cyl
loadloadcylcyl
F
L
L
F
LFLF



cos
cos
coscoscoscos
1
2
21


 For small values of ϴ and фcyl , and фload sin ϴ sin фcyl ≈ 0,
and sin ϴ sin фcyl ≈ 0
 Assuming no change on the load orientation, фload =0
load
cyl
cyl F
L
L
F
cos1
2


32. Load Displacement Through 1st class lever
 Assume no change on the orientation of
the load, and using the conservation of
energy (FcylΔcyl = Fload Δload), we have
from the previous equation for small
values of ϴ and ф
L1 L2
ϕ
ϴ
O
Fload
Fcyl
cos1
2
L
L
F
F
load
cyl
cyl
load




33. Cylinder Loading Through 2nd class lever
   
   

cossinsincoscos
0coscos
0
221
221
LFLLF
LFLLF
M
loadcyl
loadcyl
O



 Using the previous assumptions, with no change
on the load orientation, we have we have
 For small values of ϴ and ф, sin ϴ sin ф ≈ 0, and
 
  

cos
coscoscos
21
2
221
LL
L
F
F
LFLLF
cylload
cyl
loadcyl
load






L1
L2
ϕ
ϴ O
Fload
Fcyl

34. Cylinder Loading Through 3rd class lever
   
    

cossinsincoscos
0coscos
0
212
212
LLFLF
LLFLF
M
loadcyl
loadcyl
O



 In this case, we have
 For small values of ϴ and ф, sin
ϴ sin ф ≈ 0, and
 
 


cos
coscoscos
2
21
212
L
LL
F
F
LLFLF
cylload
cyl
loadcyl
load






L1 L2
ϴ O
Fload
Fcyl
ϕ

35. Buckling and Telescopic Cylinders
 Buckling occurs when the rod of the
cylinder bend or bows sideways under
the action of compressive load. The
longer and lighter the cylinder rod, the
more likely it is for it to buckle. When
selecting a cylinder from catalog, it is
important to calculate the buckling
loads.
 Telescopic cylinders allow a longer
cylinder stroke without buckling. These
cylinders have from 2 to five telescopic
sections with each section sliding inside
a larger section. They are used for lifting
platforms, tipping platforms and other
commercial vehicle applications.

36. Hydraulic Cylinders Cushions
 Double acting cylinders sometimes
contain cylinder cushions at the
end of the cylinder to slow down
the piston near the ends of the
stroke. This prevents excessive
impact when the piston is sopped
by the end caps.
 Deceleration starts when the
tapered plunger enters the
opening in the cap. This restricts
the exhaust flow from the barrel
to the ports. During the last
portion of the stroke, the oil must
exhaust through an adjustable
opening

37. Hydraulic Cylinders Cushions
 The cushion also incorporates a
check valve to allow free flow to
the barrel during the piston’s
reversed stroke.
 The maximum pressure developed
by cushions at the end of the
cylinder must be considered, since
excessive pressure buildup would
rupture the cylinder.
 Refer to example 6-6 in the book,
which illustrates how to calculate
this pressure.

38. Rotary Actuator :
Limited Rotation Actuators :
Vane Type Motor:

39. Piston Type Motor:
Limited Rotation Actuators :

40. Rotary Actuator : Continuous Rotation Actuators :
HOUSING
Unidirectional
Hydraulic motor
Bi-directional
Hydraulic motor
Gear motor:- construction similar to gear pump. It coverts hydraulic energy (pressure
energy) in to rotary mechanical energy used in many industrial application .

41. Continuous Rotation Actuators :

42. LOBE MOTOR

43. Gerotor motor

46. Axial Piston motor- Similar to axial piston pumps there are two types:-
1. Swash plate axial piston motor:- It is similar to swash plate axial piston pump. In
general it requires minimum 3 nos. piston but for uniform motion no. of piston
must be above 7 Nos.
Piston
Cylinder block

47. Bent axis piston motor:- Similar to bent axis pump. This motor consists of
i) Cylinder block having circumferentially arranged cylinder bores.
ii) Pistons
iii) Driving flange similar to swash plate
iv) Cylinder block end plate (fixed)
Pressurized oil
Used oil
Or End plate (fixed) Driving flange
(similar to swash plate)

48. Comparison between Hydraulic Pump and Motor :
Hydraulic Pump Hydraulic Motor
Pumps the hydraulic oil to system Produces rotation and torque
Mechanical energy converted into
hydraulic energy
Hydraulic energy converted into
mechanical energy
Work consuming device Work producing device
Construction of pump and motor are similar so both can be used in place
of one other.

49. Motor calculations :