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Basic Hydraulic 1/31/2015 11:32:26 AM

 Understand what is hydraulic
 Different components used in hydraulic
 Hydraulic symbol
 How to read hydraulic circuit
2

WHY HAUDRAULIC ?
 Variable Speed
 Reversible
 Overload protection
 Small Packages
 Can Be Stalled
 Less Noisy
1/31/2015 11:32:26 AMBasic Hydraulic
3

The engineering science of liquid pressure and flow.
hydraulics is used for the generation, control, and transmission of power by the
use of pressurized liquids
.
.
This drive section consists of cylinders or
hydraulic motors, depending on the application in
question
The energy control section consists of the
various valves used to provide control and
regulate the flow rate, pressure and direction of
the hydraulic fluid
The power supply section contains pump and
drive motor and the components for the
preparation of the hydraulic fluid
4

Pascal's law states that when there is an increase in
pressure at any point in a confined fluid, there is an
equal increase at every other point in the container.
Pascal's Principle and Hydraulics
5

How Hydraulic Works ?
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 6

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.
Hydraulic displacement
transmission is comparable to
the mechanical law of levers
7

Displacement transmission
The Energy transfer here
Equal 10 Kg X 10 Cm = 100 Kg
Cm
The Energy transfer here
Also is 100 Kg Cm
(1 Cm X 100 Kg = 100 Kg
Cm)
F = P X A
F1 = 10 X 10 = 100
F2 = 10 X 100 = 1000
S1= 10 Cm
S2= 1 Cm
8

FORCE PRESSURE & AREA
9
F
P A

HYDRAULIC POWER UNIT
The hydraulic power unit
(power supply unit)
provides the energy
required for the
hydraulic installation. Its
most important
components are the
reservoir (tank) , drive
(electric motor),
hydraulic pump,
pressure relief valve
(safety valve), filter and
cooler. The hydraulic
power unit may also act
as a carrier for other
devices (gauges,
directional control
valves).
10

CIRCUIT SYMBOLS FOR ENERGY TRANSFER
The symbols shown
are used in circuit
diagrams for
energy transfer
and hydraulic-fluid
preparation.
In the interests of
clarity, the lines in
the circuit diagram
should be drawn
without cross-
overs as far as
possible.
11

CIRCUIT SYMBOLS FOR ENERGY TRANSFER
The direction of
the arrows in
the circuit
symbols for
the heater
and cooler
correspond to
the direction
of heat flow
12

HYDRAULIC FLUID FILTERS
Significance
Hydraulic systems need clean and uncontaminated fluid to operate properly. Contaminants
inadvertently introduced into the hydraulic system or metal debris from normal component wear
can damage hydraulic components.
Operation
A filter element traps solid particles while allowing fluid to pass through. Many filters also use a
bypass valve that allows fluid to flow through the filter housing without passing through the
actual filter element. This allows the system to remain operational for some time, even if the filter
is clogged.
Filters used to described by nominal & absolute rating in microns.A filter nominally
rated as 10 microns, for example ,would trap most particle 10 microns in size or
larger, The Filter absolute rating however would be somewhat heigher size
,perhaps 25 microns
13

CIRCUIT DIAGRAM: RETURN FLOW FILTER
An oil filter situated in
the return line to the
tank has the
advantage that the
filter is thus easy to
maintain. A
disadvantage,
however, is that
contamination is
removed from the
hydraulic fluid only
after it has passed
through the hydraulic
components.
This configuration is
often used.
14

CIRCUIT DIAGRAM : PUMP INLET FILTER
 With this
configuration, the
pump is protected
from contamination.
The filter is, on the
other hand, less
easily accessible.
 If these filters have
a too fine mesh,
suction problems
and cavitation
effects may occur.
Additional coarse
filters upstream of
the pump are
recommended.
15

WATER COOLER
With this design of cooler,
hydraulic fluid is fed through
tubes over which coolant (water)
flows. The heat which is
discharged can be re-used
The operating temperature in
hydraulic installations should not
exceed 50 - 60ºC, since
this would cause an unacceptable
reduction in
viscosity, leading to premature aging
of the fluid. In
comparison with air cooling, operating
costs a higher due
to the required coolant and the
susceptibility to corrosion.
Temperature difference of up to
approx. 35ºC can be handled
16

HEATING ELEMENT
 Heaters are often
required to ensure
that the optimum
operating
temperature is
reached quickly.
Heating elements or
flow preheaters are
used for heating and
pre-heating
hydraulic fluid.
 If the viscosity is to
high, the resulting
increase in friction
and cavitation leads
to greater wear.
17

CIRCUIT SYMBOLS FOR ENERGY CONVERSION
Hydraulic pumps are
shown by a circle
with a part
representation of a
drive shaft.
Triangles in the
circles show the
direction of flow.
The triangles are
shown solid, since
pressure fluid is
used in hydraulics.
If the pressure
medium is
gaseous, as in the
case of
pneumatics, the
triangles are shown
in outline.
18

PUMP
Hydraulic pumps should convert mechanical energy (torque ,speed ) into
hydraulic
Energy
When choosing Pump following points must be taken in account
1. Operating medium
2. Required rang of pressure
3. Expected range of speed
4. Minimum & Maximum operating temperature
5. Installation
6. Type of drive
7. Expected life time
8. Maximum Level of noise
9. Ease of servicing
10. possible given maximum cost
Power supply section
19

PUMP
Gear pumps
Gear pumps (with external teeth) (fixed displacement) are simple and economical
pumps. The swept volume or displacement of gear pumps for hydraulics will be
between about 2 cm3 (0.002 liter) and 200 cm3 (0.2 liter). They have the
lowest volumetric efficiency of all three basic pump types (gear, vane and piston
pumps) These pumps create pressure through the meshing of the gear teeth,
which forces fluid around the gears to pressurize the outlet side
Parameter
Displacement volume : 0.02 to 200 cm3
Max Pressure : Up to 300 Bar(Size Dependent)
Rating Of speed : 500to 6000 RPM
Power supply section
20

INTERNAL GEAR PUMP
How Internal Gear Pumps Work
1. Liquid enters the suction port between the rotor (large exterior gear) and idler (small interior
gear) teeth. The arrows indicate the direction of the pump and liquid.
2. Liquid travels through the pump between the teeth of the "gear-within-a-gear" principle. The
crescent shape divides the liquid and acts as a seal between the suction and discharge ports.
3. The pump head is now nearly flooded, just prior to forcing the liquid out of the discharge port.
Intermeshing gears of the idler and rotor form locked pockets for the liquid which assures
volume control.
4. Rotor and idler teeth mesh completely to form a seal equidistant from the discharge and
suction ports. This seal forces the liquid out of the discharge port.
Parameter
Displacement Volume : 3 to 250Cm
3
Operating Pressure: Up to 300 bar
Rating Of Speed : 500 to 3000
RPM
21

PUMP
Rotary vane pumps
Rotary vane pumps (fixed and simple adjustable displacement) have higher
efficiencies than gear pumps, but are also used for mid pressures up to 180 bars
in general. Modern units can exceed 300 bars in continuous operation, although
vane pumps are not regarded as "high pressure"
The simplest vane pump is a circular rotor rotating inside of a larger circular cavity.
The centers of these two circles are offset, causing eccentricity. Vanes are
allowed to slide into and out of the rotor and seal on all edges, creating vane
chambers that do the pumping work. On the intake side of the pump, the vane
chambers are increasing in volume. These increasing volume vane chambers
are filled with fluid forced in by the inlet pressure. Inlet pressure is actually the
pressure from the system being pumped, often just the atmosphere. On the
discharge side of the pump, the vane chambers are decreasing in volume,
forcing
Power supply
section
22

PUMP
Screw pumps
Screw pumps (fixed displacement) are a double Archimedes' screw, but closed. This means that two
screws are used in one body. The pumps are used for high flows and relatively low pressure
(max 100 bar). They were used on board ships where the constant pressure hydraulic system
was going through the whole ship, especially for the control of ball valves, but also for the
steering gear and help drive systems. The advantage of the screw pumps is the low sound level
of these pumps; the efficiency is not that high.
The major problem of screw pumps is the hydraulic reaction forces which is transmitted axially
opposed to the flow direction,
23

PUMP
Piston Pump
All Piston pump operate on principle of that a piston reciprocating in abore will drae fluid in as it is
retracted & expel it as it moves forward
Two basic design is available
1. A radial piston pump piston arrange radially in cylinder block
2. Axial Piston pump piston in axial units are parallel to each other
& to axis of the cylinder
Piston pumps are highly efficient unit ,available in a wide range of capacities
.They are capable of operating medium to high pressure range (1500-3000
psi)
Axial piston pump may be further divided in to inline(swash
plate) & bent axis type
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PUMP
Radial piston pump
The outer ring for bracing of the pumping pistons is in eccentric position to the
hollow shaft in the center. This eccentricity determines the stroke of the pumping
piston.
The piston starts in the inner dead center (IDC) with suction process. After a
rotation angle of 180° it is finished and the workspace of the piston is filled with
the to moved medium. The piston is now in the outer dead center (ODC). From
this point on the piston displaces the previously sucked medium in the pressure
channel of the pump.
Animation
25

RADIAL PISTON PUMP ANIMATION
Return
26

PUMP
Axial piston pump
An axial piston pump has a number of pistons (usually an odd
number) arranged in a circular array within a housing which is
commonly referred to as a cylinder block, rotor or barrel. This
cylinder block is driven to rotate about its axis of symmetry by an
integral shaft that is, more or less, aligned with the pumping
pistons (usually parallel but not necessarily).
27

PUMP
Axial piston pumps using the swashplate principle
Like radial piston pump ,the displacement of axial piston pump s is determine by the size & number of piston
,as well as stroke length
In variable displacement model s of the inline pump ,the swash plate is installed in movable yoke
Pivoting the yoke on pintled change the swash plate angle to increase or decrease the piston stroke
The yoke can be positioned by any several means ,including manual control, pressure& load sensing &
pressure limiter control compensator control
Maximum angle on this unit is limited by construction to 17.5 degrees
Fix displacement Variable displacement
28

WOBBLE PLATE PISTON PUMP
 This pump has pistons in a stationary block, and a rotating wobble plate. There might
be 4, 5, or more pistons (usually an odd number are used) -- only two shown here.
 Each piston has a valve within it and another valve behind it. Fluid comes in on the
wobble plate side (on the bottom left in this drawing) and exits under pressure in the
back (on the right here).
 The pistons are pushed against the wobble plate with large springs. A pair of smaller
springs force the valves (small metal balls) closed. The spring inside the piston is
fairly weak, since only suction is used to force it open.
 This type of pump can develop incredible pressure -- 10,000 P.S.I. or more. It is
commonly used for low-volume applications. ergency fuel pumps on some early
aircraft.
29

PUMP
Bent Axis Pump.
Bent axis piston pumps have a rotating cylinder containing parallel pistons
arranged radially around the cylinder centre line. The cylinder is driven by an
shaft which is arranged at an angle to the cylinder axis. the shaft includes a
flange with a mechanical connection to each piston. As the shaft rotates the
pistons are made to reciprocate over a stroke based on the relative angle of the
shaft and cylinder.
The displacement of this pump varies between 0 to 30 degree .Fix
displacement model are usually availabe eith 23 to 30 degrees .In variable
displacement ,yoke with externally control is used to change the angle ,with
some control
30

CIRCUIT SYMBOLS FOR HYDRAULIC MOTORS
The symbols for
hydraulic motors
are
distinguished
from the
symbols for
hydraulic pumps
by the fact that
the arrows
showing the
direction of flow
are the other
way round.
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HYDRAULIC MOTORS
A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and
angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder.
Conceptually, a hydraulic motor should be interchangeable with a hydraulic pump because it performs
the opposite function
It has to be part of a hydraulic circuit that incorporates a hydraulic pump along with other hydraulic gadgetry
such as valves, filters, high-pressure hoses, metal tubing, hydraulic fluid reservoir etc.
The pump draws hydraulic fluid from the reservoir and supplies it under pressure to the hydraulic motor
linked mechanically to the workload. The pump receives mechanical power for its operation through a
prime mover that is either an internal combustion engine or an electric motor.
Where electric motors, which can deliver only rotational power and must be sized to suit the load application,
hydraulic motors are much smaller in size even when the application involves heavy loads. In a heavy
electromechanical system a big electric motor needs to be directly located on the motion axis which
may not be always feasible
For the same application, a relatively small hydraulic motor can be placed with ease and connected to a
pump located remotely within the system through an arrangement of high-pressure flexible hoses that
can be conveniently routed even through disadvantageous twists and bends.
32

HYDRAULIC MOTOR APPLICATIONS
Due to the high torque at low speeds, loaders and other construction equipment use heavy hydraulic motors to drive the
wheels for moving the machines around. There is one motor for each wheel and the diesel engine is used to drive the
pump, which deliver hydraulic fluid to the motors. A hydraulic motor with the right specifications needs to be fitted to
enable the machine to function properly.
1. Oil pipeline inspection equipment
2. Undersea camera manipulation
3. Jumbo jet maintenance jacks
4. Milling and sawing applications
5. Dynamite blast hole pump drive
6. Automatic clamping
7. Textile washing agitators
8. Orange peeling machines
9. Fan drives
10. Diamond wheel dresser
11. Drill and tap machine tool
12. Chicken processing machinery
13. Conveyor drives
14. Electric motor coil winding
33

TYPES OF HYDRAULIC MOTORS
 Hydraulic motors delivering rotary power are mainly of two types and are classified on torque
and rotational speed. One is referred to as HSLT or High Speed Low Torque and the other as
LSHT or Low Speed High Torque motor.
 The LSHT motor can have a speed range from 0.1 to 1000 revolutions per minute whereas
HSLT motor speeds can range from 1000 to 5000 revolutions per minute.
 The size advantage can be gauged from the fact that the size of a 5hp hydraulic motor will be
roughly that of a 350ml beer can. In addition, there would be very low level noise and vibration
generation and much higher efficiency. HSLT and LSHT.
Hydraulic motors are available in different types
1
2
3 Piston
Radial
Axial
Gear
Vane
34

Gear type hydraulic motors
can be classified as internal gear or 'gerator' type and external gear motors.
Gerator motors are very quiet in operation and designed to transmit rotary power
through an output shaft connected to a rotor moving inside an outer stator.
Supply of hydraulic fluid under pressure makes the rotor move eccentrically
along the inner periphery of the stator. An external gear hydraulic motor has a
set of meshing gears enclosed in a sealed housing have passages supply and
return of hydraulic fluid. Pressurized hydraulic fluid flowing into the housing has
an action on the gear teeth and makes the gears rotate. The rotational
movement of the gears is transmitted to the workload through an output shaft
connected to the rotating gears and passing through the motor housing.
Internal gear type (Gerator) 35

A radial piston hydraulic motor
has a bank of cylinders arranged like a car engine with a series of pistons riding on cams along a
camshaft, which is attached to the output shaft. The reciprocating movement of the pistons gives
rotary movement to the camshaft/output shaft that is tapped for power. In another variation
cylinders are arranged radially like that of an aircraft engine with the pistons moving inwards to
push against a cam located in center causing it to rotate. The cam is mechanically linked to the
output shaft/workload. Yet another type of radial piston hydraulic motor with cylinders placed
radially like an aircraft engine has the pistons moving outwards to push against cams in a
housing that surrounds the motor. This makes the housing rotate. The rotating housing is tapped
for power. These motors are generally used as wheel motors and for other suitable applications
like forklifts
They are available in displacements from 40cc/rev up to about 12 litres/rev
Crankshaft type Radial Piston Motors are capable of running at "creep" speeds and some can run
seamlessly up to 1500 rpm whilst offering virtually constant output Torque chacteristics. This
makes them still the most versatile design.
36

Vane type hydraulic motors
have movable vanes connected to a centrally
located output shaft. The whole arrangement
is enclosed in a housing/ case that receives
hydraulic fluid under pressure from the
pump. This fluid exerts force of the vanes to
make them move like fan blades. This action
results in rotating the output shaft, which is
tapped for power.
37

Axial piston motors
The axial piston motor is of the 'swashplate type' and has a bank of
cylinders arranged in a circle (360 degrees) parallel to each other. Each
cylinder has a piston, which reciprocates with one end of the piston
pushing against an eccentric swash-plate located at one end of the bank
of cylinders. There is a mechanical arrangement through which the
eccentric plate is connected to an output shaft that is axially aligned with
the cylinders. During motor operation, the cylinders are filled with high-
pressure hydraulic fluid in a particular sequence making the pistons
move outwards to push sequentially against the swash-plate causing it
to rotate. On the return stroke of the piston the fluid is swept back at low
pressure to return to a reservoir. The operation imparts rotational
movement to the output shaft, of which one end is connected to the
swash-plate and other to the workload. This is a design that caters to a
very compact cylindrical hydraulic motor. Most axial hydraulic motors are
HSLT.
38

CIRCUIT SYMBOLS FOR SINGLE ACTING CYLINDERS
Single acting cylinders
have one port, i.e.
pressure fluid can be
applied only to the
piston side. With
these cylinders, the
return stroke is
produced either by
external force, shown
in the symbol by an
opening bearing cap,
or by a spring is
shown within the
symbol in this latter
case.
39

CIRCUIT SYMBOLS FOR DOUBLE ACTING CYLINDERS
Double acting cylinders have
two ports to allow pressure
fluid to be applied to both
cylinder chambers. The
symbol for a differential
cylinder is distinguished
from the symbol for a
double acting cylinder by
the two lines added to the
end of the piston rod. The
area ratio is generally 2:1.
In the case of cylinders
with double- ended piston
rods, the symbol shows
that the piston areas are of
equal size (synchronous
cylinders
40

WHAT ARE HYDRAULIC CYLINDERS?
An actuation device that makes use of a pressurized hydraulic
fluid is known as a hydraulic pump.
This mechanism is used for producing linear motion and force in
applications that transfer power. In other words, a hydraulic
cylinder converts the energy stored in the hydraulic fluid into a
force used to move the cylinder in a linear direction.
Barrel
Piston
rod
Piston
Seal
41

CYLINDER CUSHIONING
42
Cushioning of some sort normally is required to decelerate a cylinder's piston before
it strikes the end cap. Reducing the piston velocity as it approaches the end cap
lowers the stresses on cylinder components and reduces vibration transmitted to

PARTS OF A HYDRAULIC CYLINDER
Cylinder barrel
The cylinder barrel is mostly a seamless thick walled forged pipe that must be machined internally. The cylinder
barrel is ground and/or honed internally
Cylinder base or cap
In most hydraulic cylinders, the barrel and the bottom portion are welded together. This can damage the inside of
the barrel if done poorly. Therefore, some cylinder designs have a screwed or flanged connection from the
cylinder end cap to the barrel. (See "Tie rod cylinder", below) In this type the barrel can be disassembled and
repaired.
Cylinder head
The cylinder head is sometimes connected to the barrel with a sort of a simple lock (for simple cylinders). In general,
however, the connection is screwed or flanged. Flange connections are the best, but also the most
expensive. A flange has to be welded to the pipe before machining. The advantage is that the connection is
bolted and always simple to remove. For larger cylinder sizes, the disconnection of a screw with a diameter
of 300 to 600 mm is a huge problem as well as the alignment during mounting.
Piston
The piston is a short, cylindrical metal component that separates the two parts of the cylinder barrel internally. The
piston is usually machined with grooves to fit elastomeric or metal seals. These seals are often O-rings, U-
cups or cast iron rings. They prevent the pressurized hydraulic oil from passing by the piston to the chamber
on the opposite side.
piston rod
The piston rod is typically a hard chrome-plated piece of cold-rolled steel which attaches to the piston and extends
from the cylinder through the rod-end head. In double rod-end cylinders, the actuator has a rod extending
from both sides of the piston and out both ends of the barrel. The piston rod connects the hydraulic actuator
to the machine component doing the work.
Rod gland
The cylinder head is fitted with seals to prevent the pressurized oil from leaking past the interface between the rod
and the head. This area is called the rod gland. It often has another seal called a rod wiper which 43

CLASSIFICATION OF CYLINDERS ACCORDING TO SPECIFICATIONS
Plunger Cylinders:
These cylinders are also known as Ram cylinders. These types of hydraulic cylinders are placed in
an upright position. This is done so that once the supply of the fluid is stopped, the weight on the
cylinder will make it return to its original position. The cylinders used in automobile service
centers are a good example of the plunger cylinders.
Telescoping Cylinders
Telescopic cylinders are also known as multistage hydraulic cylinders. These cylinders have at the
most six stages. These are specially used in applications where there is less area. Telescopic
cylinders can either be single action or double action. The stroke of these cylinders is long and is
used in applications such as cranes and forklifts, etc.
Cable Cylinders
The cable cylinders can either be hydraulic or pneumatic powered cylinders that are of the double
acting type. These cylinders have long strokes and produce moderate force. The cable cylinders
can be operated in limited space.
Diaphragm Cylinders
Diaphragm cylinders are of two types i.e. flat diaphragm and rolling diaphragm. These cylinders have
zero leak around the piston.
44

CLASSIFICATION OF CYLINDERS ACCORDING TO FUNCTION
Single Acting Cylinders:
In single acting cylinders the fluid is pressurized from only one side
of the cylinder during both the expansion as well as the retraction
process. A spring or an external load is used to return the cylinder
top to its original position i.e. when pressure of the fluid is cut off.
Double Acting Cylinders
In the double acting cylinders, the pressure from the fluid is applied
in both the directions. Single cylinders that consist of springs are
not used in large stroke applications because there are inherent
mechanical problems associated with the spring. The double
acting rods could be of two types:
• Single rod ended
• Double rod ended
45

DIRECTION CONTROL VALVES
Direction control valves are use in hydraulic system to
direct the flow of fluid in a desired direction & location
in the circuit
There are two fundamental positions of directional
control valve namely normal position where valve
returns on removal of actuating force and other
is working position which is position of a valve when
actuating force is applied.
46

CIRCUIT SYMBOLS FOR DIRECTIONAL CONTROL VALVES
Designations for directional
control valves always give
firstly the number of ports
and then the number of
switching positions.
Directional control valves
always have at least two
ports and at least two
switching positions. The
number of squares shows
the number of possible
switching positions of a
valve. Arrows within the
squares show the direction of
flow. Lines shown how the
ports are interconnected in
the various switching
positions of the valve. The
designations always relate to
the normal position of the 47

This illustration shows
the circuit symbols for
4/2- and 5/2-way valves.
There are two general methods for the
designation of ports, using either the letters
P, T, R, A, B and L or consecutively using
A, B, C, D etc.; the first method is the
preferred one in the relevant standard
48

The
illustration
shows the
circuit
symbols for
4/3-way
valves with
various
mid-
positions
49

CIRCUIT SYMBOLS FOR MANUAL OPERATION
The switching position of a
directional control valve
can be changed by various
actuation methods. The
symbol for the valve is
accordingly supplemented
by a symbol indicating the
actuation methods shown,
such as pushbuttons and
pedals, a spring is always
necessary for resetting.
Resetting can, however,
also be achieved by
actuating the valve a
second time, for example
in the case of valves with
hand levers and detents.
50

CIRCUIT SYMBOLS FOR MECHANICAL ACTUATION
This illustration
shows the
symbols for
stem or push
button, spring
and roller
stem
51

CIRCUIT SYMBOL FOR PRESSURE VALVES
 Pressure valves are
represented using
squares. The flow
direction is indicated by
an arrow. The valve
ports can be designated
as P (supply port) and T
(tank return port) or as A
and B. The position of
the arrow within the
square indicates
whether the valve is
normally open or
normally closed.
Adjustable pressure
valves are indicated by a
diagonal arrow through
the spring. Pressure
valves are divided into
pressure relief valves
and pressure regulators.
52

PRESSURE RELIEF VALVES
53

PRESSURE REDUCING VALVE
54

CIRCUIT SYMBOLS FOR FLOW CONTROL VALVES
 A distinction is made in flow
control valves between types
which are affected by viscosity
and those which are unaffected.
Flow control valves unaffected by
viscosity are termed orifices. A 2-
way flow control valve consists of
restrictors, one adjustable
restrictor which is unaffected by
viscosity (orifice) and a regulating
restrictor (pressure
compensator). These valves are
represented by a rectangle
containing the symbol for the
adjustable restrictor and an arrow
to represent the pressure
compensator. The diagonal arrow
through the rectangle indicates
that the valve is adjustable.
55

CIRCUIT SYMBOLS FOR NON-RETURN VALVES
The symbol for non-return
valves is a ball which is
pressed against a seat.
Delockable non-return
valves are shown by a
square containing the
symbol for a non-
return valve. The pilot
control for unlocking
the non- return valve is
indicated by a broken
line at the pilot port.
The pilot port is
designated by the
letter X.
56

CIRCUIT SYMBOLS FOR MEASURING DEVICES
The illustration
shows the
symbols for
measuring
devices used in
hydraulics
57

ACCUMLATOR
A hydraulic accumulator is a pressure storage reservoir in which a non-
compressible hydraulic fluid is held under pressure by an external
source. The external source can be a spring, a raised weight, or a
compressed gas. An accumulator enables a hydraulic system to cope
with extremes of demand using a less powerful pump, to respond more
quickly to a temporary demand, and to smooth out pulsations. It is a type
of energy storage device.
Compressed gas accumulators, also called hydro-pneumatic
accumulators, are by far the most common type.
58

TYPES OF ACCUMULATORS
 Towers
 Raised weight
 Compressed gas (or gas-charged) closed
accumulator
 Compressed gas open accumulator
 Spring type
 Metal bellows type
59

COMPRESSED GAS ACCUMULATOR
It is widely used accumulator in
present scenario. It is popularly
known as “hydro-pneumatic
accumulator”. It apply force to the
liquid by using a compressed gas
that acts as the spring. It uses
inert gas (nitrogen) under pressure
that provides the compressive
force on fluid. Oxygen is not used
because oxygen and oil can form
an explosive mixture when
combined under pressure As the
volume of the compressed gas
changes the pressure of the gas,
and pressure of the fluid, changes 60

BLADDER TYPE ACCUMULATOR
bladder accumulator consists of seamless high-
pressure cylinder with an internal elastomeric
bladder with pressurized nitrogen on it and
hydraulic fluid on the other(external) side. The
accumulator is charged with nitrogen through
a valve installed on the top. The accumulator
will be pre-charged to nominal pressure when
the pumps are not operating. The maximum
flow rate of the accumulator is controlled by
the opening orifice and the pressure difference
across the opening. Bladder material widely
used are epichlorohydric rubber(ECO) and
Acrylonitrile butadiene rubber
ADVANTAGES : Fast acting
Not susceptible to contamination
Consists behavior under similar
conditionLIMITATIONS :
Compressed ratio is limited, approximately 4:1
Bladder failure.(NBR).
61

PISTON TYPE ACCUMULATOR
This accumulator consists of a cylinder
assembly, a piston assembly, and
two end-cap assemblies. An
accumulator contains a free-floating
piston with liquid on one side of the
piston and pre-charged air or
nitrogen on the other side. An
increase of liquid volume decreases
the gas volume and increases gas
pressure, which provides a work
potential when the liquid is allowed
to dis-charged.
ADVANTAGES :
High compression ratio up to 10:1
Higher flow rate than bladder type
.LIMITATIONS :
They are more susceptible to fluid
contamination Lower response
time than the bladder and 62

METAL BELLOW ACCUMULATOR
The metal bellows accumulator is similar
to bladder type, expect the elastic is
replaced by a hermitically sealed
welded metal bellows. Fluid may be
internal or external to the bellows.
Internal It is used when a fast
response time is not critical, yet
reliability is important. Metal bellow
types are pre-charged by supplier
and then permanently sealed leading
to a maintenance free accumulator.
LIMITATIONS :
Response time is more
High cost External
63

SPRING TYPE ACCUMULATOR
 It uses the energy stored in springs
to create a constant force on the
liquid contained in an adjacent ram
assembly. The load characteristics
of a spring are such that the energy
storage depends on the force
required to compress s spring. The
free (uncompressed) length of a
spring represents zero energy
storage. As a spring is compressed
to the maximum installed length,
high pressure value of the liquid in a
ram assembly is established. As
liquid under pressure enters the ram
cylinder, causing a spring to
compress, the pressure on the liquid
will rise because of the increased
loading required to compress the 64

FUNCTIONS OF ACCUMULATOR
 Emergency and safety: An accumulator which is kept constantly under
pressure is valuable in the event of an electrical power failure as it can
provide flow and pressure to perform an additional function or
complete a machine cycle.
 Shock or pulsation dampening: An accumulator can be used to
cushion the pressure spike from sudden valve closure, the pulsation
from pumps or the load reaction from sudden movement of parts
connected to hydraulic cylinders.
 Leakage compensation: An accumulator can be used to maintain
pressure and make-up for lost fluid due to internal leakage of system
components including cylinders and valves.
 Thermal expansion: An accumulator can absorb the pressure
differences caused by temperature variations in a closed hydraulic
system.
 Noise reduction: An accumulator is effective at reducing hydraulic
system noise caused by relief valves, pump pulsations, system shock
and other circuit generated noises.
65

ACCUMLATOR SYMBOL
66

HYDEAULLIC HOSE
67

HYDRAULIC HOSE
Hydraulic tubes are seamless steel precision pipes, specially manufactured for hydraulics. The tubes have
standard sizes for different pressure ranges, with standard diameters up to 100 mm. The tubes are supplied by
manufacturers in lengths of 6 m, cleaned, oiled and plugged. The tubes are interconnected by different types of
flanges (especially for the larger sizes and pressures), welding cones/nipples (with o-ring seal), several types of
flare connection and by cut-rings. In larger sizes, hydraulic pipes are used. Direct joining of tubes by welding is not
acceptable since the interior cannot be inspected.
Hydraulic pipe is used in case standard hydraulic tubes are not available. Generally these are used for low
pressure. They can be connected by threaded connections, but usually by welds. Because of the larger diameters
the pipe can usually be inspected internally after welding. Black pipe is non-galvanized and suitable for welding.
Hydraulic hose is graded by pressure, temperature, and fluid compatibility. Hoses are used when pipes or tubes
can not be used, usually to provide flexibility for machine operation or maintenance. The hose is built up with
rubber and steel layers. A rubber interior is surrounded by multiple layers of woven wire and rubber. The exterior is
designed for abrasion resistance. The bend radius of hydraulic hose is carefully designed into the machine, since
hose failures can be deadly, and violating the hose's minimum bend radius will cause failure. Hydraulic hoses
generally have steel fittings swaged on the ends. The weakest part of the high pressure hose is the connection of
the hose to the fitting. Another disadvantage of hoses is the shorter life of rubber which requires periodic
replacement, usually at five to seven year intervals.
Tubes and pipes for hydraulic applications are internally oiled before the system is commissioned. Usually steel
piping is painted outside. Where flare and other couplings are used, the paint is removed under the nut, and is a
location where corrosion can begin. For this reason, in marine applications most piping is stainless steel.
68

HYDEAULLIC HOSE
 SAE 100R1 hose should be used with petroleum- and water-based
hydraulic fluids, within a temperature range from140° to 100° C.
 Type A consists of an inner tube of oil-resistant synthetic rubber, a
single wire braid reinforcement, and an oil- and weather-resistant
synthetic rubber cover. A ply, or braid, of suitable material may be
used over the inner tube or over the wire reinforcement (or both) to
anchor the synthetic rubber to the wire.
 Type AT has the same construction as Type A, except AT has a
cover designed to assemble with fittings that do not require removal
of the cover or any portion of it.

 SAE 100R2 hose should be used with petroleum- and water-based
hydraulic fluids, within a temperature range from140° to 100° C. It
consists of an inner tube of oil-resistant synthetic rubber, steel-wire
reinforcement according to hose type, as detailed below, and an oil-
and weather-resistant synthetic rubber cover. A ply, or braid, of
suitable material may be used over the inner tube and/or over the
wire reinforcement to anchor the synthetic rubber to the wire.
 Type A has two braids of wire reinforcement
 Type B has two spiral plies and one braid of reinforcement
 Type AT is the same as Type A, but AT has a cover designed to
assemble with fittings that do not require removal of the cover or
any portion of it.
 Type BT is the same as Type B, but BT has a cover designed to
assemble with fittings that do not require removal of the cover or
any portion of it.
69

HYDEAULLIC HOSE
 SAE 100R3 hose should be used with petroleum-
and water-based hydraulic fluids, within a
temperature range from140° to 100° C. It is
constructed with an inner tube of oil-resistant
synthetic rubber, two braids of suitable textile yarn,
and an oil- and weather-resistant synthetic rubber
cover.

 SAE 100R4 hose should be used in low pressure
and vacuum applications, with petroleum- and
water-based hydraulic fluids, within a temperature
range from140° to 100° C. It is constructed with an
inner tube of oil-resistant synthetic rubber, a
reinforcement consisting of a ply, or plies, of
woven or braided textile fibers with a suitable
spiral of body wire, and an oil- and weather-
resistant synthetic rubber cover.
70

HYDEAULLIC HOSE
 SAE 100R5 hose should be used with
petroleum- and water-based hydraulic fluids,
within a temperature range from140° to 100°
C. It is constructed with an inner tube of oil-
resistant synthetic rubber reinforced with two
textile braids separated by a high-tensile-
strength steel-wire braid. All of the braids are
impregnated with an oil- and mildew-
resistant synthetic rubber compound.

 SAE 100R6 hose (above) should be used
with petroleum- and water-based hydraulic
fluids within a temperature range from140° to
100° C. It consists of an inner tube of oil-
resistant synthetic rubber, one braided ply of
suitable textile yarn, and an oil- and weather-
resistant synthetic rubber cover.
71

HYDEAULLIC HOSE
 SAE 100R7 thermoplastic hose (above)
should be used for synthetic, petroleum-,
and water-based hydraulic fluids in a
temperature range from140° to 93° C. It
consists of a thermoplastic inner tube
resistant to hydraulic fluids with suitable
synthetic-fiber reinforcement and a
hydraulic fluid- and weather-resistant
thermoplastic cover. Nonconductive 100R7
is identified with an orange cover and
appropriate lay line. Its pressure capacity is
similar to that of 100R1.

 SAE 100R8 hose is high-pressure
thermoplastic hose that should be used with
synthetic, petroleum- and water-based
hydraulic fluids within a temperature range
from140° to 93° C. It consists of a
thermoplastic inner tube resistant to
hydraulic fluids with suitable synthetic-fiber
reinforcement and a hydraulic fluid- and
weather-resistant thermoplastic cover.
Nonconductive 100R8 is identified with an
orange cover and appropriate lay line. Its
pressure capacity is similar to that of 72

 SAE 100R9 hose should be used with petroleum- and water-based hydraulic
fluids within a temperature range from 140° to 100° C.
 Type A consists of an inner tube of oil-resistant synthetic rubber, four spiral
plies of wire wrapped in alternating directions, and an oil- and weather-
resistant synthetic rubber cover. A ply, or braid, of suitable material may be
used over the inner tube and/or over the wire reinforcement to anchor the
synthetic rubber to the wire.
 Type AT has the same construction as Type A, but AT has a cover designed
to assemble with fittings that do not require removal of the cover or any
portion of it.

 SAE 100R10 hose should be used with petroleum- and water-based hydraulic
fluids within a temperature range from140° to 100° C.
 Type A consists of an inner tube of oil-resistant synthetic rubber, four spiral
plies of heavy wire wrapped in alternating directions, and an oil- and weather-
resistant synthetic rubber cover. A ply, or braid, of suitable material may be
used over the inner tube and/or over the wire reinforcement to anchor the
 Type AT has the same construction as Type A, but AT's cover is designed to
assemble with fittings that do not require removal of the cover or any portion
73

HYDEAULLIC HOSE
 SAE 100R11 hose should be used with petroleum- and
water-based hydraulic fluids within a temperature
range from 140° to 100° C. It consists of an inner tube
of oil-resistant synthetic rubber, six spiral plies of heavy
wire wrapped in alternating directions, and an oil- and
weather-resistant synthetic rubber cover. A ply, or
braid, of suitable material may be used over the inner
tube and/or over the wire reinforcement to anchor the

range from 140° to 121° C. It consists of an inner tube
of oil-resistant synthetic rubber, four spiral plies of
heavy wire wrapped in alternating directions, and an
oil- and weather-resistant synthetic rubber cover. A ply,
or braid, of suitable material may be used over the
inner tube and/or over the wire reinforcement to
anchor the synthetic rubber to the wire. 74

HYDEAULLIC HOSE
and water-based hydraulic fluids, within a
temperature range from 140° to 121° C. It is
constructed with an inner tube of oil-resistant
synthetic rubber, followed by multiple spiral plies of
heavy wire wrapped in alternating directions, and
concluding with an oil- and weather-resistant
synthetic rubber cover. A ply, or braid, of suitable
material may be used over the inner tube and/or over
the wire reinforcement to anchor the synthetic rubber
to the wire.

 SAE 100R14 hose should be used with petroleum-,
synthetic-, and water-based hydraulic fluids within a
temperature range from 154° to 204° C.
 Type A consists of an inner tube of
polytetrafluorethylene (PTFE) reinforced with a single
braid of type 303XX stainless steel.
 Type B has the same construction as Type A, but B
has the additional feature of an electrically-
conductive inner surface to prevent buildup of an 75

HYDEAULLIC HOSE
based hydraulic fluids within a temperature range from
140° to 121° C. It consists of an inner tube of oil-
resistant synthetic rubber, multiple spiral plies of heavy
wire wrapped in alternating directions, and an oil- and
weather-resistant rubber cover. A ply, or braid, of
suitable material may be used over or within the inner
tube and/or over the wire reinforcement to anchor the

range from140° to 100° C. It consists of an inner tube of
oil-resistant synthetic rubber, steel wire reinforcement of
one or two braids, and an oil-and weather-resistant
synthetic rubber cover. A ply, or braid, of suitable
material may be used over the inner tube and/or over
the wire reinforcement to anchor the synthetic rubber to
the wire.
76

HYDRAULIC FLUID
 Hydraulic fluids, also called hydraulic liquids, are the
medium by which power is transferred in hydraulic
machinery. Common hydraulic fluids are based on
mineral oil or water.Examples of equipment that might
use hydraulic fluids include excavators and
backhoes, hydraulic brakes, power steering systems,
transmissions, garbage trucks, aircraft flight control
systems, lifts, and industrial machinery.
 Hydraulic systems like the ones mentioned above will
work most efficiently if the hydraulic fluid used has
low compressibility.
77

HYDRAULIC OIL FUNCTIONS AND PROPERTIES
Function & property
Medium for power transfer and control
1. Low compressibility (high bulk modulus)
2. Fast air release
3. Low foaming tendency
4. Low volatility
Medium for heat transfer
1. Good thermal capacity and conductivity
Lubricant
Viscosity for film maintenance
Low temperature fluidity
Thermal and oxidative stability
Hydrolytic stability / water tolerance
Cleanliness and filterability
Demulsibility
Antiwear characteristics
Corrosion control 78

HYDRAULIC OIL FUNCTIONS AND PROPERTIES
Pump efficiency
1. Proper viscosity to minimize internal leakage
2. High viscosity index
Special function
Fire resistance
Friction modifications
Radiation resistance
Environmental impact
Low toxicity when new or decomposed
Biodegradability
79

CHARACTERISTICS OF A GOOD HYDRAULIC FLUID
Viscosity
 Viscosity is a measure of a hydraulic fluid's resistance to flow. It is a hydraulic
fluid's most important characteristic and has a significant impact on the operation
of the system.
 When a hydraulic oil is too thin (low viscosity), it does not seal sufficiently. This
leads to leakage and wear of parts. When a hydraulic oil is too thick (high
viscosity), the fluid will be more difficult to pump through the system and may
reduce operating efficiency.
 All hydraulic fluids must be able to retain optimum viscosity during operation in
cold or hot temperatures, in order to consistently and effectively transmit power. .
 Compressibility
 Compressibility is a measure of the amount of volume reduction due to pressure.
Although hydraulic oils are basically incompressible, slight volume reductions can
occur under certain pressure ranges.
 Compressibility increases with pressure and temperature and has significant
effects on high-pressure fluid systems. It causes servo failure, efficiency loss, and
cavitation; therefore, it is important for a hydraulic oil to have low compressibility.
80

 Wear Resistance
Wear resistance is a hydraulic fluid's ability to reduce the wear
rate in frictional boundary contacts. Antiwear hydraulic fluids
contain antiwear components that can form a protective film on
metal surfaces to prevent abrasion, scuffing, and contact fatigue.
Antiwear additives enhance lubricant performance and extend
equipment life.
 Oxidation Stability
Oxidation stability is a hydraulic oil's resistance to heat-induced
degradation caused by a chemical reaction with oxygen.
Hydraulic oils must contain additives that counteract the process
of oxidation, improve the stability and extend the life of the fluid.
Without these additives, the quality of the hydraulic oil will
deteriorate quickly.
81

 Thermal Stability
Thermal stability is the ability to resist breakdown at elevated temperatures. Antiwear
additives naturally degrade over time and this process can be accelerated at higher
temperatures. The result of poor thermal stability is the formation of sludge and varnish
which can clog filters, minimize flow and increase downtime. In addition, as these
antiwear agents decompose at high temperatures, acids are formed which attack bronze
and yellow metals in piston pumps and other hydraulic system components. Hydraulic oils
can be formulated with very high levels of thermal stability to minimize these issues and
help extend the life of the hydraulic fluid and the components of the hydraulic system.
 Filterability
Water can react with additives in hydraulic fluids forming oil insoluble material. These
contaminants can precipitate from the lubricant and block filters, valves and other
components resulting in decreased oil flow or the system going on bypass. Blockage can
eventually result in unplanned downtime. Hydraulic fluids are designed to be filtered with
modern filtration systems without fear of the additive being depleted or removed from the
system. This enables systems to stay clean without sacrificing critical performance
requirements such as antiwear, rust protection or foam inhibition.
82

 Rust and Corrosion Protection
 In many systems, water can enter as condensation or contamination, and mix with the
hydraulic oil. Water can cause rusting of hydraulic components. In addition, water can react with
some additives to form chemical species which can be aggressive to yellow metals. Hydraulic
oil formulations contain rust and corrosion inhibitors which prevent the interaction of water or
other chemical species from attacking metal surfaces.
 Foam Resistance
Foam results from air or other gases becoming entrained in the hydraulic fluid. Air enters a
hydraulic system through the reservoir or through air leaks within the system.
A hydraulic fluid under high pressure can contain a large volume of dissolved or dispersed air
bubbles. When this fluid is depressurized, the air bubbles expand and produce foam. Because of
its compressibility and poor lubricating properties, foam can seriously affect the operation and
lubrication of machinery.
Proper foam inhibitors modify the surface tension on air bubbles so they more easily break up.
83

 Demulsibility
Water that enters a hydraulic system can mix or emulsify with the hydraulic oil. If this 'wet'
fluid is circulated through the system, it can promote rust and corrosion. Highly refined
mineral oils permit water to separate or demulsify quickly. However, some of the additives
used in hydraulic oils promote emulsion formation, preventing the water from separating
and settling out of the fluid. Demulsifier additives are incorporated to promote water
separation from hydraulic fluids.
 Hydrolytic Stability
When hydraulic fluids come into contact with water, the water can interact with the additive
system of the hydraulic oil resulting in the formation of acids. Hydraulic fluids that lack
hydrolytic stability hydrolyze in the presence of water to form oil insoluble inorganic salts
that can block filters and valves inhibiting oil flow. This can result in hydraulic system
failure. Properly formulated hydraulic fluids are designed to contain additives that are
resistant to interactions with water, helping to extend the life of the equipment.
84

 Seal Compatibility
 Leaking hydraulic fluids can cause many issues from simple
housekeeping problems to more serious safety concerns and
lubrication failures. Most hydraulics systems utilize rubber
seals and other elastomers to minimize or prevent hydraulic
oil leakage. Exposure of the elastomer to the lubricant under
high temperature conditions can cause the rubber seals to
harden, crack and eventually leak. On the other hand,
hydraulic oil exposure can seals to swell excessively
preventing hydraulic valves and pistons from moving freely.
Hydraulic oils are tested against a variety of seal materials to
ensure that the hydraulic fluid will be compatible with seals
under various conditions.
85

BASIC HYDRAULIC CIRCUIT
86

87
Control of a Single Acting
Hydraulic
Cylinder
Two Position
Three Way
Manually Actuated
Spring Offset DCV

88
Control of a Double Acting
Hydraulic Cylinder
Three Position
Four Way
Manually Actuated
Spring Centered DCV

89
Regenerative Circuit
1) Pressurized fluid
discharge returned
to system
2)Speed up
extending speed
3) Retraction bypass
A regeneration circuit can double the extension speed of a single-
rod cylinder without using a larger pump. This means that
regeneration circuits save money because a smaller pump, motor,
and tank can produce the desired cycle time. It also means that
the circuit costs less to operate over the life of the machine.

90
Drilling Machine Application
1) Spring centered
position – Rapid
spindle advance
2) Left envelope –
Slow feed
3) Right envelope –
Retracts piston

91
PUMP Unloading circuit
1) Unloading valve
unloads the pump
at the ends of
extending and
retracting strokes
2) As well as in
spring centered
position of DCV

92
Double Pump Hydraulic System
1)Punch Press
Initial Low
Pressure high
flow rate req.
2)When punching
operation begins,
increased
pressure opens
unloading valve
to unload low
pressure pump.

93
Counterbalance Valve
To keep vertically
mounted cylinder in
upward position while
pump is idling.
Counterbalance
valve is set to open
at slightly above the
pressure required to
hold the piston up.

94
Hydraulic Cylinder
Sequence
Circuit
1)Left Env: Left Cyl
extends completely
and then Right Cyl
extend.
2)Right Env: Right Cyl
retracts fully and
then Left Cyl
retracts.

95
Cylinder Synchronizing
Circuit
Pump pressure should overcome load
acting on both cylinders.
P1Ap1- P2(Ap1-Ar1) = F1
P2Ap2- P3(Ap2-Ar2) = F2

96
Fail Safe Circuit
Designed to prevent injury to operator or
damage to equipment.
Prevent Cylinder from
accidentally falling on an
Operator in the event of:
Hydraulic line ruptures
Person inadvertently operates
manual override on Pilot
actuated DCV when pump not
operating

97
Two hand Safety Circuit
Designed to protect
an operator from
injury.
For circuit to
function, operator
must depress both
manually actuated
valves.
Any one button
prevents operation.

98
Hydraulic Motor Braking System

OPEN & CLOSE CIRCUIT
99
As Open Loop the pumps have a Suction line connected
to tank and an Outlet line connected to Directional
Control Valves like most hydraulic circuits no matter the
pump type. The Directional Control Valves determine
actuator function and direction. They can be Fixed
Volume, Pressure Compensated and/or Variable
Volume.
As Closed Loop the flow lines are directly connected to
an actuator (Commonly a Hydraulic Motor) and all oil
leaving one pump flow port goes to the actuator and all
oil from the actuator returns to the opposite pump flow
port.
In closed loop system, one additional pump is used for
making up the circuit fluid. And the direction of the
direction of the movement of the actuator is controlled
by the swash plate of the variable displacement pump.
The open loop hydraulic system has advantage of less
heat generation and on the other hand the closed loop
circuit is preferred for better (precise) response of the

CYLINDER CUSHIONING
100

Closed Circuit One-Direction
Closed Circuit that
of motor rotation.
Motor speed varied by
changing pump
displacement.
Torque capacity of motor
adjusted by pressure
setting of the relief valve
101

102
Closed Circuit Reversible
Direction
Hydrostatic Transmission

2014916 635220964350095000

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