Hydraulic actuators are used to convert hydraulic pressure into mechanical motion or force. The main types are linear actuators like hydraulic cylinders, rotary actuators like motors, and semi-rotary actuators. Hydraulic cylinders come in single-acting, double-acting, telescopic, and tandem varieties. Double-acting cylinders use hydraulic pressure on both sides of the piston to extend and retract the rod. Telescopic cylinders extend in stages for a long stroke and short retracted length. Tandem cylinders apply pressure to multiple pistons to produce increased force from a small cylinder diameter. Cushioning devices are used on cylinders to control deceleration and prevent shock at the end of the stroke.

1. UNIT-II
HYDRAULIC ACTUATORS AND
CONTROL COMPONENTS

2. HYDRAULICACTUATORS

3. ACTUATORS
Hydraulic systems are used to control and transmit power.
A pump driven by prime mover such as electric motor
creates a flow of fluid in which the pressure, directionand
flow rate are controlled by valves
An actuator is used to convert the energy of fluid back into
mechanical power.
The amount of output power developed depends upon the
flow rate, pressure drop across the actuator and its overall
efficiency
Thus they are devices which used to convert pressure
energy of the fluid into mechanical energy.

4. TYPES
Depending on the type of actuation, hydraulic actuators are
classified as,
1. Linear actuator: for linear actuation (hydraulic cylinder)
2. Rotary actuator: for rotary actuation(hydraulic motor)
3. Semi-rotary actuator: for limited angle of actuation (semi-
rotary actuators)

5. HYDRAULIC LINEAR
ACTUATORS
As their name implies, it provides motion in a straight line.
The total movement is a finite amount determined by the
construction of the unit
They are referred to as cylinders, rams and jacks
The function of a hydraulic cylinder is to convert the hydraulic
power into linear mechanical force or motion
Hydraulic cylinder extend and retract a piston rod to provide a
pull or push force to drive the external load along a straight path

6. TYPES OF HYDRAULIC
CYLINDERS
Hydraulic cylinder are of following types:
• Single-acting cylinders
• Double-acting cylinders
• Telescopic cylinders
• Tandem cylinders

7. SINGLE ACTING CYLINDER

9. SINGLE ACTING CYLINDER
• It consist of piston inside a cylindrical housing called as
barrel
• On one end is attached a rod, which can reciprocate
• At the opposite end, there is a port for the entrance and
exit of the oil
• They produce force only in one direction by hydraulic
pressure acting on the piston
• The return of the spring is not done hydraulically, it is
either done by gravity or spring.

10. DOUBLE ACTING CYLINDER
There are two types of double acting cylinder:
• Double acting cylinders with piston rod on one side
• Double acting cylinders with piston rod on both side

11. DOUBLE ACTING CYLINDER

12. DOUBLE ACTING CYLINDER
DOUBLE ACTING CYLINDER WITH PISTON ROD ON ONE
SIDE
• To extend the cylinder, the pump flow is sent to the blank-
end port as shown in fig.
• The fluid from the rod end port returns to the reservoir
• Now to retract the cylinder, the pump flow is sent to the
rod end port and the fluid from the blank end port returns
to the tank as shown in another fig.

13. DOUBLE ACTING CYLINDER
DOUBLE ACTING CYLINDER WITH A PISTON ROD ONBOTH
SIDES

14. DOUBLE ACTING CYLINDER
• A double acting cylinder with piston on both sides is a
cylinder with a rod extending from both the ends
• The application involves in a process where work can be
done by both the ends of the cylinder, thereby making the
cylinder more productive
• Double rod cylinder can withstand higher side loads
because they have an extra bearing on each rod to
withstand the loading.

15. TELESCOPIC CYLINDER
A telescopic cylinder is needed when a long strokelength
and a short retracted length are needed.
The telescopic cylinder extends in stages, each stage
consisting of a sleeve that fits inside the previous stage
One application for this type of cylinder is raising a dumping
truck bed.
Telescopic cylinders are available both in single acting and
double acting models.

16. TELESCOPIC CYLINDER

17. TELESCOPIC CYLINDER
Construction:
• They generally consist a nest of tubes and operate on the
displacement principle
• The tubes are supported by bearing rings, the innermost set
of which have grooves or channels to allow the fluid flow
• The front bearing assembly on each section includes seals
and wiper rings
• Stop rings limit the movement of each section, thus
preventing the separation
• For a given input flow rate, the speed of operation increases
in steps as each successive section reaches the end of its
stroke. Similarly, for a specific pressure, the load shifting
capacity decreases for each of the successive section

18. TANDEM CYLINDER

19. TANDEM CYLINDER
• A tandem cylinder is used in application where a large
amount of force is required to be applied from a small
diameter cylinder
• Pressure is applied to both the pistons, resulting in a
increased force because of a large area.
• The only drawback is that this cylinders must be longer
than a standard cylinder to achieve an
because the flow must go to both
equal speed
the pistons
simultaneously.

20. GRAPHICAL SYMBOLS

21. GRAPHICAL SYMBOLS

22. CUSHIONING OF CYLINDERS

23. CUSHIONING OF CYLINDERS
• For prevention of shock due to stopping loads at the end
of piston stroke, cushion devices are used.
• Cushion may be applied at either end or both the ends
• They operate on the principle that as the cylinder piston
approaches the end of the stroke, an exhaust fluid is
forced to go through an adjustable needle valve that is set
to control the escaping fluid at the given rate.
• This allows the deceleration characteristic to be adjusted
for different loads
• When the cylinder piston is actuated, the fluid enters the
cylinder port and flows through a little check valve so that
the entire piston area can be utilized to produce forces
and motion.

24. OPERATION OF CYLINDER
CUSHIONING

25. OPERATION OF CYLINDER
CUSHIONING

26. CUSHIONING PRESSURE
• During deceleration, extremely high pressure may be
developed within a cylinder cushion.
• The action of the cushioning device is to set up a back
pressure to decelerate the load.

27. MAXIMUM SPEEDS IN
CUSHIONED CYLINDERS
The maximum speed of the cushion rod is limited by the rate
of fluid flow into and out of the cylinder and the ability of the
cylinder to withstand the impact forces that occurs when the
piston motion is arrested by the cylinder end plate.
• For uncushioned cylinder: 8 m/min
• For cushioned cylinder : 12 m/min
• For high speed or externally cushioned cylinders: 30
m/min

28. ACCELERATION &
DECELERATION OF CYLINDER
LOADS
Cylinders are subject to acceleration and deceleration during
their operation. Cylinders are decelerated to provide
cushioning and cylinders are accelerated to reduce cycle
time of the operation.
Acceleration Equation:
v  u at
v2
 u 2
 2as
s  ut 
1
at2
2

29. QUESTIONS
• Explain the classification of hydraulic actuators.
• Explain various types of hydraulic cylinders.
• Describe the construction and working of double-acting cylinders.
• Derive an expression for force, velocity and power for hydraulic
cylinders.
• Explain the importance of cylinder cushioning.
• Explain various types of cylinder mountings used in fluid power.
• Evaluate the performance of hydraulic systems using cylinders.