nota pneumatic and hydraulic system

HYDRAULIC SYMBOLS

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9.2 ENERGY TRANSFER AND STORAGE

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9.3 OPEN AND CLOSE LOOP CONTROL OF ENERGY

9.3.1 Open loop control system

Figure 9.1 Open loop control system

In this system, a control valve spool must be open in the center to allow
pump flow to pass through the valve and return to the reservoir. Figure
9.1 shows this system in the neutral position. To operate several
functions simultaneously, an open loop control system must have the
correct connections. An open loop control system is efficient on single
functions but is limited with multiple functions.

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9.3.2 Close loop control system

Figure 9.2 Close loop control system
In this system, a pump can rest when the oil is not required to operate a
function. This means that a control valve is closed in the center, stopping
the flow of the oil from the pump. Figure 9.2 shows a close loop control
system.

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9.4 FLUID STORAGE AND PREPARATION

9.4.1 Reservoir

The reservoir in a hydraulic system fulfills several tasks, it:
 Acts as intake and storage reservoir for the hydraulic fluid required for

operation of the system.
 Dissipates heat
 Separates air, water and solid materials
 Supports a built-on pump and drive motor and other hydraulic

components, such as valves, accumulators, etc.

Figure 9.3 Structure of hydraulic reservoir

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From these functions, the following guidelines can be drawn up for the
design of the reservoir. Reservoir size, dependent on:
 Pump delivery
 The heat resulting from operation in connection with the maximum

permissible liquid temperature
 The maximum possible difference in the volume of liquid which is

produced when supplying and relieving consuming devices (e.g
cylinders, hydraulic fluid reservoirs)
 The place of application
 The circulation time

Figure 9.4 Hydraulic power pack & pilot operated double non return valve

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9.5 MEASURING DEVICES AND INDICATORS

Figure 9.5 Measuring devices

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SUMMARY

In this chapter we have studied to :

REFERENCES

1. Fundamentals Of Pneumatic Control Engineering Text Book, Festo Didactic, 1989
2. Electro-Pneumatics Basic Level TP 201 Text Book, Festo, 1998
3. FluidSim Pneumatic Software Version 4.0

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HYDRAULIC COMPONENTS

CHAPTER 10 : HYDRAULIC COMPONENTS

INTRODUCTION

LEARNING OBJECTIVES

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10.1 HYDRAULIC PUMPS

The pump in a hydraulic system, also known as a hydraulic pump, converts the
mechanical energy in a drive unit into hydraulic energy (pressure energy).
The pump draws in the hydraulic fluid and drives it out into a system of lines. The
resistances encountered by the flowing hydraulic fluid cause a pressure to build
up in the hydraulic system. The level of the pressure corresponds to the total
resistances which result from the internal and external resistances and the flow
rate.
 External resistances, come about as a result of maximum loads and

mechanical friction and static load and acceleration forces.
 Internal resistances, come about as a result of the total friction in the lines

and components, the viscous friction and the flow losses (throttle points).

10.1.1 Three basic types of hydraulic pump can be distinguished on the basis of
the displacement volume:
 Constant pumps
 Fixed displacement volume
 Adjustable pumps
 Adjustable displacement volume
 Variable capacity pumps
 Regulation of pressure, flow rate or power, regulated
displacement volume.

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Hydraulic pumps

Gear pump Rotary vane pump Piston pump
External gear pump Internally pressurized Radial piston pump
Internal gear pump Externally pressurized Axial piston pump
Annular gear pump

Screw pump

Constant pump Constant, adjustable and variable capacity pump

Figure 10.1 Categorized of hydraulic pump

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10.1.2 Example of hydraulic pump: Gear pump
Pressure area

Trapped fluid

Figure 10.2 Gear pump

- One gear is connected to the drive, the other is turned by the
meshing teeth. The increase in volume which is produced when
a tooth moves out of a mesh, causes a vacuum to be generated
in the suction area.

- The hydraulic fluid fills the tooth gaps and is conveyed
externally around the housing into pressure area P.

- The hydraulic fluid is then forced out the tooth gaps by the
meshing of teeth and displaced into the lines.

- Fluid is trapped in the gaps between the teeth between suction
and pressure area.

- This liquid is fed to the pressure area via a groove since
pressure peaks may arise owing to compression of the trapped
oil, resulting in noise and damage.

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10.2 DIRECTIONAL CONTROL VALVES

Directional control valves are components which change, open or close flow
paths in hydraulic systems. They are used to control the direction of motion of
power components and the manner in which these stop.

Figure 10.3 2/2 way valve

10.2.1 The following rules apply the representation of directional control valves:
 Each different switching position is shown by a square
 Flow directions are indicated by arrows
 Blocked ports are shown by horizontal lines
 Ports are shown in the appropriates flow direction with line arrows
 Drain ports are drawn as a broken line and labeled (L) to distinguish
them from control ports.

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10.2.2 There are two types of directional control valve:
 Continuously operating directional control valves
- In addition to two end positions, these valves can have any
number of intermediate switching positions with varying throttle
effect.
 Digitally operating directional control valve
 These always have a fixed number (2,3,4……) of switching
positions. In practice, they are known simply as directional control
valves.

10.2.3 Directional control valves are classified as follows according to the
number of ports:
 2/2 way valve
 3/2 way valve
 4/2 way valve
 5/2 way valve
 4/3 way valve

The diagram on the following page shows the symbols used for
directional control valves

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BPLK Figure 10.4 Directional control valves basic symbols

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10.3 HYDRAULIC CYLINDERS

10.3.1 Cylinders (linear actuators)

Cylinders are drive components which convert hydraulic power into
mechanical power. They generate linear movements through the
pressure on the surface of the movable piston. Distinction is made
between the following types of cylinder:

10.3.1.1 Single acting cylinder
The fluid pressure can only be applied to one side of the piston
with the result that the drive movement is only produced in one
direction. The return stroke of the piston is effected by an
external force or by return spring.
Example :
 Hydraulic ram
 Telescopic cylinder

10.3.1.2 Double acting cylinder
The fluid pressure can be applied to either side of the piston
meaning that drive movements are produced in twodirections.
Example:
 Telescopic cylinder
 Differential cylinder
 Sychronous cylinder

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Figure 10.5 Types of cylinders

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10.3.2 Motors (rotary actuators)

Like cylinders, hydraulic motors are drive components controlled by
valves. They too convert hydraulic power into mechanical power with the
difference that they generate rotary or swivel movements instead of linear
movements.

Figure 10.6 Hydraulic motor

10.4 NON-RETURN VALVE

Non return valves block the flow in one direction and permit free flow in the other.
As there must be no leaks in the closed direction, these valves are always of
poppet design and are constructed according to the following basic principle.
The sealing element (generally a ball or cone) is pressed againts an
appropriately shaped seat. The valve is opened by volumetric flow in the flow
direction, the sealing element being lifted from the seat.

Non return valves are distinguished as follows:
 Non-return valves (unloaded, spring loaded)
 Lockable and unlockable non-return valves.

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Figure 10.7 Non return valve symbols

Figure 10.8 Non return valve

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10.4.1 Example circuit for non-return valve

Figure 10.9 Non return valve for pump protection

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10.5 FLOW CONTROL VALVE

Flow control valve are used to reduce the speed of a cylinder or the r.p.m of a
motor. On the basis of their controlling or regulating function, flow control valves
are calssified as either:
 Flow control valves or,
 Flow regulating valves.

Figure 10.10 Restrictors and orifice valves

10.5.1 One way flow control valve

Where the restrictor is only effective in one direction is a combination of a
restrictor and non-return valve. The restrictor controls the flow rate in a
single direction dependent on flow. In the opposite direction, the full
cross-sectional flow is released and the return flow is at full pump
delivery. This enables the one way flow control valve to operate as
follows:

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The hydraulic flow is throttled in the flow direction from A to B. This
results in flow divsion as with the restrictor. Flow to the power component
is reduced, the speed being reduced correspondingly.

 Flow is not restricted in the opposite direction (B to A) as the sealing
cone of the non-return valve is lifted from its valve seat and the full
cross-sectional flow is released.

 With adjustable one-way flow control valves, the throttling point can
either be enlarged or reduced.

Figure 10.11 One way flow control valve

10.5.2 Two way flow control valves

As has already been described in the section on restrictors, there is an
interrelationship between pressure drop ∆p via throttle point must be kept
constant. Therefore a restrictor (adjustable) and a second restrictor
(pressure balance) are built-in for the desired flow rate. These restrictors
change their resistance according to the pressures present at the input
and output of the valve. The total resistance of the two restrictors
combined with the pressure relief valve causes the flow division.

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Figure 10.12 Two way flow control valve

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The regulating restrictor can be installed either ahead of or behind the
adjustable restrictor.
The valve is open in the normal position. When flow passes through the
valve, input pressure p1 is produced ahead of the adjustable restrictor. A
pressure drop ∆p is produced at the adjustable restrictor, i.e p2 < p1. A
spring must be installed on the side F2 so that the regulating restrictor
retains its equilibrium. This spring causes the constant pressure
difference across the adjustable throttle. If a load passes from the
consuming device to the valve output, the regulating restrictor reduces
the resistance by the amount by which the load has increased.

10.6 PRESSURE CONTROL VALVE

10.6.1 Pressure valve

Pressure valve have a task of controlling and regulating the pressure in a
hydraulic systemand in parts of the system.

10.6.1.1 Pressure relief valve
 The pressure in a system is set and restricted by these
valves. The control pressure is sensed at the input (P) of the
valve.

10.6.1.2 Pressure regulators
 These valves reduce the output pressure where there is a
varying higher input pressure. The control pressure is
sensed at the output of the valve.

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Figure 10.13 Pressure valves

10.6.2 Pressure relief valve

Pressure relief valve operate accoding to the following principle:
 The input pressure (p) acts on the surface of the sealing element and

generates the force F = p1 . A1
 The spring force which the sealing element is pressed onto the seat is

adjustable.
 If the force generated by the input pressure exceeds the spring force,

the valve starts to open. This causes a partial flow of liquid to the tank.
If the input pressure continues to increase, the valve opens until the
complete pump delivery flows to the tank.
 Resistances at the output (tank line, return line, filter or similar) act on
the surface A2. The resultant force must be added to the spring force.
The output side of the valve may also be pressure-compensated (see
figure 10.15, pressure relief valve with cushioning and pressure
compensation).

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 Cushioning pistons and throttles are often installed in pressure relief
valve to eliminate fluctuations in pressure. The cushioning device
shown here causes:
- Fast opening
- Slow closing of the valve

 By these means, damage resulting from pressure surges is avoided
(smooth valve operation).

 Pressure knocks arise when the pump supplies the hydraulic oil to the
circuit in an almost unpressurised condition and the supply port is
suddenly closed by a directional control valve.

a) b)

Figure 10.14 Pressure relief valve a)sectional b)circuit diagram

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Figure 10.15 Pressure relief valve with cushioning (sectional diagram)

Pressure relief valve are used as:
 Safety valves

A pressure relief is termed a safety valve when it is attached to the
pump, for example, to protect it from overload. The valve setting is
fixed at the maximum pump pressure. It only opens in case of
emergency.
 Counter-pressure valves
These counteract mass moments of inertia with tractive loads. The
valve must be pressure-compensated and the tank connection must
be loadable.
 Brake valves
These prevent pressure peaks, which may arise as a result of mass
moments of inertia on sudden closing of the directional control valve.
 Sequence valves (sequence valves, pressure sequence valves)
These open the connection to other consuming devices when the set
pressure is exceeded.

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There are both internally and externally controlled pressure relief
valves. Pressure relief valves of poppet or slide design may used as
sequence valves when the pressure is compensated and loading at
the tank connection has no effect on the opening characteristics.

Figure 10.16 Application example (brake valve)

10.7 FILTERS

Filters are of great significance in hydraulic systems for the reliable functioning
and long service life of the components.

Figure 10.17 Effect of polluted oil

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Contamination of the hydraulic fluid is caused by:
 Initial contamination during commisioning by metal chips, foundry sand, dust,

welding beads, scale, paint, dirt, sealing materials, contaminated hydraulic
fluid (supplied condition)
 Dirt contamination during operation owing to wear, ingress via seals and tank
ventilation, filling up or changing the hydraulic fluid, exchanging components,
replacing hoses.

10.7.1 Filter arrangement

Hydraulic filters can be arranged in various different positions within a
system. A distinction is made between:
 Filtering of the main flow: return, inlet and pressure filtering
 Filtering of the by-pass flow: only one part of the delivery is filtered.

Figure 10.18 Filter arrangement

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SUMMARY

In this chapter we have studied to :

REFERENCES

1. Fundamentals Of Pneumatic Control Engineering Text Book, Festo Didactic, 1989
2. Electro-Pneumatics Basic Level TP 201 Text Book, Festo, 1998
3. FluidSim Pneumatic Software Version 4.0

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CHAPTER 11 : INSTALLATION OF HYDRAULIC CIRCUIT

INTRODUCTION

LEARNING OBJECTIVES

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11.1 CONTROL OF SINGLE & DOUBLE ACTING CYLINDER

11.1.1 Exercise 1(Triggering single acting cylinder)

11.1.2 Exercise 2 (Triggering double acting cylinder)

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11.2 CONTROL WITH 4/2, 4/3 VALVE

11.2.1 Exercise 3 (4/2 way valve with pump protection using non return valve)

11.2.2 Exercise 4 (4/2 way valve control)

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11.2.3 Exercise 5 (Pump bypass)

11.2.4 Exercise 6 (Locking stage)

0 Bar

?

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11.3 SPEED CONTROL OF HYDRAULIC CYLINDER

11.3.1 Exercise 7 (Restrictor-flow division)

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11.3.2 Exercise 8 (2way flow control valve)

11.3.3 Exercise 9 (2 way flow control valve , loading of consuming devices,
idling)

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11.3.4 Exercise 10 (2 way flow control valve , loading of consuming devices,
underload)

11.3.5 Exercise 11(2 way flow control valve with other consuming devices)

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11.4 CONTROL WITH PRESSURE REGULATING VALVE,
PRESSURE SEQUENCE VALVE

11.4.1 Exercise 12(Pressure relief valve)

11.4.2 Exercise 13 (Brake valve)

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11.4.3 Exercise 14 (Counter balance valve)

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SUMMARY

In this chapter we have studied to :

REFERENCES

1. Fundamentals Of Pneumatic Control Engineering Text Book, Festo Didactic, 1989
2. Electro-Pneumatics Basic Level TP 201 Text Book, Festo, 1998
3. FluidSim Pneumatic Software Version 4.0

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ELECTRO-HYDRAULICS OVERVIEW AND APPLICATION

CHAPTER 12 : ELECTRO-HYDRAULIC OVERVIEW AND
APPLICATION

INTRODUCTION

LEARNING OBJECTIVES

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12.1 ELECTRO-HYDRAULICS CONTROL

12.1.1 Hydraulic and electro-hydraulic control

Hydraulic and electro-hydraulic control systems both exhibit a hydraulic
power section. However, the signal control section is constructed
differently.
 In the case of hydraulic control systems, this section is mainly carried

out manually. It is rare for the signal control to be effected by means
of a hydraulic circuit, which then comprises foe example shuttle valve.
 In the case of an electro-hydraulic control system, the signal control
section is constructed using electrical components, which include for
example electrical input keys, proximity sensors, pressure switches,
relays or programmable logic controller.
In the case of both types control, the directional control valves form the
interface between the signal section and the hydraulic power section.

Figure 12.1 Signal flow and components of a hydraulic control system

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Figure 12.2 Signal flow and components of an electro-hydraulic control system

Hydraulic and electro-hydraulic control systems also differ in respect of the
representative of the circuit diagram.
 The purely hydraulic control system is represented by means of a single

overail circuit diagram.
 Electro-hydraulic control system are represented in two circuit diagrams. One

circuit diagram represents the electrical section and the other circuit diagram
the hydraulic section of the control system.

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a)

b)

Figure 12.3 Electro-hydraulic circuit diagram a) hydraulic circuit b) electric circuit

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12.2 CHARACTERISTIC AND APPLICATION

12.2.1 Design of the electrohydraulic control system

Electro-hydraulic control systems can be designed in very different ways.
The following has to be decided:
 Is signal processing to be realised by means of a PLC or a relay

circuit?
 Can the control functions of a drive or those of an associated drive be

combined into one block?
 What measures can be used to eliminate malfunction and is

preventive maintenance suppoted? Such mesures are for example
sensors, measuring systems, whereby the operating status of the
system can be followed.
 Are advanced components such as bus system to be used?
 Is a modular control concept possible? This includes for example the
use of identical circuit and program modules for different control
systems.

12.2.2 Selection of components for the control system

The function of the control system is to combine the energy supply
system with the drive section in accordance with particular specifications.
The control system comprises cmponents for signal flow and energy flow.
These include:
 The hydraulic drives,
 The hydraulic valves,
 The control elements,
 The sensors,
 The PLC or the type of relays to be used.

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The following criteria is to be taken into account when selecting the
various finalcontrol elements:
 Mode of operating,
 Static and dynamic behaviour,
 Efficiency,
 Space requirement,
 Costs,
 Reliability,
 Safety considerations,
 Maintenance required.

12.2.3 Circuit design

The last step of the design process deals with the preparation and
completion of all the documentation required to construct and program
the control system. These includes:
 The part list,
 The hydraulic circuit design,
 The electrical diagram,
 The terminal diagram.
 And if a PLC is used, the design of a PLC program.

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12.2.4 Example of application
The piston rod of a cylinder is to advance if pusbutton S1 is pressed, to
remain in the forward end position for ten seconds and to retract again
automatically.

a1

y1 y2

s1 a1 k1 t1

k1 t1 y 1 y2

BPLK Figure 12.4 Example application of electro-hydraulic circuit

The diagram shows the electrical circuit diagram for delayed retracting.
The piston rod advances if pushbutton S1 is pressed. When the forward
end position is reached, limit switch a1 closes and current flows through
coil t1. Contact t1 still remains open for the duration of the time delay.
Only when the time delay has elapsed, does contact t1 close and the
piston rod retract.

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