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HYDRAULICS & PNEUMATICS
Presented by: Dr. Abootorabi
IntroductionComponents
1
Introduction
Three basic methods of transmitting power:
Electrical
Mechanical
Fluid power
In practice, most applications actually use combination of
the three methods to achieve the most efficient overall
systems. 2
Introduction
We have to understand the features of each method in
order to get the best result.
For example, fluid systems can transmit power more
economically over greater distance compare to
mechanical systems. But fluid systems are restricted
to shorter distances compared to electrical systems.
3
Definition
Hydraulics is the
science of forces and
movements transmitted
by means of liquids.
4
Comparison of power system
5
Comparision of power system
6
Applications of hydraulic power
Machine-tool construction is a
typical area of application of
hydraulics. With modern CNC
machine tools, the tools and
workpieces are clamped by
hydraulic means. Feed motions
and the spindle drive can also
be hydraulically powered.
7
Machine tools
Press with elevated reservoir
This is an application in which extremely
high forces are required.
A special feature is the elevated reservoir,
which utilizes the static pressure in the
pressure medium.
8
Applications of hydraulic power
Mobile hydraulics: Excavator
On this hydraulic
excavator, not only all
working movements
(linear drives) but also
the propulsion of the
vehicle (rotary drive) are
hydraulically powered.
The primary drive of the
excavator is an internal-
combustion engine.9
Applications of hydraulic power
Fluid power is divided into two: hydraulic system
(using oils) and pneumatic system (using compressed
air).
Each system has its own advantages and drawbacks.
There are many factors to consider to choose a
suitable system.
10
Fluid power
Advantages of fluid power can be summarized as
follows:
11
Ease and accuracy of control
Multiplication of force
Constant force or torque
Simplicity, safety, economy
Hydraulic oils are messy and leakage is impossible to
eliminate completely.
Hydraulic lines can burst and might result in injuring
people and damaging surrounding objects.
Prolonged exposure to loud noise can damage hearing.
Most hydraulic oils can cause fires if there is a leakage.
Compressive air for pneumatic systems can be dangerous
if the pressure is too high.
12
Drawbacks of fluid power
Structure of a hydraulic system
This simplified block
diagram shows the division
of hydraulic systems into a
signal control section and a
hydraulic power section.
This signal control section is
used to activate the valves
in the power control
section.
13
Hydraulic power sectionThe diagram of the hydraulic power
section is complemented in this case by a circuit diagram to allow correlation of the various function groups; the power supply section contains the hydraulic pump and drive motor and the components for the preparation of the hydraulic fluid. The power control section consists of the various valves used to provide control and regulate the flow rate, pressure and direction of the hydraulic fluid. The drive section consists of cylinders or hydraulic motors, depending on the application in question. 14
Components of a fluid power system: Hydraulic system
A hydraulic system has six basic components:
A tank to hold the hydraulic oil
A pump to force the oil through the system
An electric motor or other power source to drive the
pump
Valves to control oil direction, pressure and flow rate
An actuator to convert the pressure of the oil into
mechanical force or torque to do useful work
Piping to carry the oil from one location to another 15
Components of a fluid power system: Hydraulic system
16
• A tank (reservoir) to hold the hydraulic oil (A)• An electronic motor or other power source to drive the pump (B)• A pump to force the oil through the system (C)• Valves to control oil direction, pressure and flow rate (D-G)• An actuator to convert the pressure of the oil into mechanical force or torque to do useful work (H)• Piping to carry the oil from one location to another
Components of a fluid power system: Pneumatic
system
A pneumatic system also has six basic components:
An air tank to store a certain volume of compressed air
A compressor to compress the air coming from the atmosphere
An electric motor or other prime mover to drive the compressor
Valves to control air direction, pressure, and flow rate.
Actuators, which are similar in operation to hydraulic actuators
Piping to carry the pressurized air from one location to another
17
Components of a fluid power system: Pneumatic
systemA pneumatic system also has six basic components:
18
Primary functions of a hydraulic fluidTransmit power
Lubricate moving parts
Seal clearance between mating parts
Dissipate heat
19
Hydraulic fluid In order to be safe, hydraulic fluids must also be
changed periodically.
The frequency of changing depends on the fluid as well
the operating conditions.
Advice from laboratory analysis could be sought to
determine when the fluid should be changed.
20
Fluids: liquids and gasesA liquid is a fluid which has a definite volume
independent of the shape of its container.
A liquid is considered to be incompressible so that its
volume does not change with pressure changes.
This is only approximation but the change in volume
due to pressure change is quite small that it is ignored
for most engineering purposes.
21
Fluids: liquids and gasesA gas is a fluid which is compressible.
In addition, its volume will vary to fill the vessel
containing it.
A gas is greatly influenced by the pressure to which it is
subjected.
If the pressure increases, the volume decreases, and
vice versa.
22
Fluids: liquids and gasesAir is the only gas commonly used in fluid power
systems because it is inexpensive and readily
available.
Air has the following desirable features:
1. Fire resistant
2. Not messy
3. Can be released back to atmosphere
23
Disadvantages of airDue its compressibility, air cannot be used in an application
requiring accurate positioning or rigid holding.
Because air is compressible, it tends to be sluggish.
Air can be corrosive since it contains oxygen (about 21%) and
water.
A lubricant must be added to air to lubricate valves and actuators.
High pressure air (greater than 250 psi = 17 atm) is typically not
used due to the explosive dangers.
24
Hydrostatic pressureHydrostatic pressure is the pressure
created above a certain level within
a liquid as a result of the weight of
the liquid mass. Hydrostatic
pressure is not dependent on the
shape of the vessel concerned but
only on the height and density of
the column of liquid.
Hydrostatic pressure can generally
be ignored for the purpose of
studying hydraulics.
25
Pressure propagation
If a force F acts on an area A
of an enclosed liquid, a
pressure p is produced
which acts throughout the
liquid (Pascal's Law).
26
Power transmission If a force F1 is applied to an area
A1 of a liquid, a pressure p
results. If, as in this case, the
pressure acts on a larger surface
A2, then a larger counter-force F2
must be maintained. If A2 is three
times as large as A1, then F2 will
also be three times as large as F1.
Hydraulic power transmission is
comparable to the mechanical law
of levers. 27
Displacement transmission
If the input piston of the
hydraulic press travels a
distance s1, a volume of fluid
will be displaced. This same
volume displaces the output
piston by the distance s2. If
the area of this piston is
larger than that of the input
piston, the distance s2 will be
shorter than s1.28
Pressure transferThe fluid pressure p1 exerts a force F1 on the
surface A1 which is transferred via the piston rod
to the small piston. The force F1 thus acts on the
surface A2 and produces the fluid pressure p2 .
Since the piston area A2 is smaller than the
piston area A1, the pressure p2 must be larger
than the pressure p1.
The pressure-transfer (pressure-intensification)
effect is put to practical use in
pneumatic/hydraulic pressure intensifiers and
also in purely hydraulic systems when extremely
high pressures are required which a pump
cannot deliver. 29
Types of flowA distinction is made between laminar
flow and turbulent flow. In the case of
laminar flow, the hydraulic fluid moves
through the pipe in ordered cylindrical
layers. If the flow velocity of the
hydraulic fluid rises above a critical
speed, the fluid particles at the center
of the pipe break away to the side, and
turbulence results.
Turbulent flow should be avoided in
hydraulic circuits by ensuring they are
adequate sized.30
Types of flowLaminar
Turbulent
31
CavitationMotion energy is required for an
increase in the flow velocity of the oil at
a restriction. This motion energy is
derived from the pressure energy. If the
vacuum which results is smaller than -
0.3 bar, air dissolved in the oil is
precipitated out. When the pressure
rises again due to a reduction in speed,
the oil bursts into the gas bubbles.
Cavitation is a significant factor in
hydraulic systems as a cause of wear in
devices and connections. 32
CavitationLocal pressure peaks occur during cavitation. This causes the
erosion of small particles from the wall of the pipe immediately after
the reduced cross-section, leading to material fatigue and often also
to fractures. This effect is accompanied by considerable noise.
33
Components of a hydraulic system
34
Components of a hydraulic system Power supply section:
35
Components of a hydraulic system Power supply section:
36
Components of a hydraulic system Power supply section:
37
Components of a hydraulic system Hydraulic fluid:
38
Valves:
Components of a hydraulic system Types of valves:
1. Directional control valves:
39
Components of a hydraulic system 2. Pressure valves:
00
40
Components of a hydraulic system 3. Flow control valves:
41
Components of a hydraulic system 4. Non-return valves:
42
Components of a hydraulic system Cylinders (linear actuators):
43
1. Single-acting Cylinders:
Components of a hydraulic system Cylinders (linear actuators):
2. Double-acting cylinders:
44
Components of a hydraulic system Motors (rotary actuators):
45
Tank (reservoir) for a hydraulic system:
The function of a tank is to store the fluid used. However, it serves functions other than storage and is actually a working part of the system.
A hydraulic reservoir or tank has the following functions:Stores the hydraulic fluid of the system, including some
reserveProtects the stored fluid from outside contaminationProvides means to check the amount of fluid in the systemProvides means to add or change the fluidCools the fluid as it returns from the actuators, and Removes contaminants such as water, dirt, pieces of
metal, or chemicals from the fluid
46
Components of a hydraulic system
Tank (reservoir) of a hydraulic system47
Components of a hydraulic system
Tank (reservoir) of a hydraulic system48
Components of a hydraulic system
Components of a hydraulic system Most tanks are of welded construction with supports for
mounting for easy access to the drain plug and also to
permit cooling air to circulate underneath.
A tank must be totally enclosed and should have a filtered
air breather to screen out particles from the surrounding air.
The fluid that flows in the hydraulic system must be
cleaned. Contaminant are screened out using a strainer and
a filter. Some reservoirs have magnetic plugs to trap iron
and steel particles carried by the fluid.
49
Components of a hydraulic system
A strainer blocks the relatively large solid particles
from entering the system. It is attached to the pump
inlet line and may immersed in the oil near the bottom
of the tank. Particles stuck to the strainer are cleaned
off later and the strainer is ready for reuse.
A filter is used to remove smaller particles by
absorbing them. Fluid is allowed to flow through but
fine particles are trapped and absorbed. When the
filter becomes clogged, it is replaced by a new one.
50
Strainers and Filters:
Strainers are constructed of a fine wire screen that usually
has openings more than 150 micron or μm.
A strainer only moves the larger particles.
The condition of the strainer can be monitored by installing a
pressure gage between the pump and the strainer. A pressure
drop shown by the gage indicated that the strainer is
becoming clogged. If the strainer is not cleaned, the pump
can be starved, resulting in cavitations and increased pump
noise. 51
Components of a hydraulic system
Basically, filters and strainers are similar. However, the size of
particles that can be removed by a strainer is normally
greater than 150 μm. On the other hand, a filter can remove
much smaller particles, down to 1 μm.
Even particles as small as 1 μm can produce a damping effect
on hydraulic systems and can also accelerate oil
deterioration.
52
Components of a hydraulic system
The end.
53