87413621 pneumatics circuit

A J AY C H A C K O

P R 11 M E 1 0 0 2

PNEUMATIC CIRCUITS

PNEUMATICS

Pneumatics system uses pressurised air to transmit

and control power. (or) Pneumatics is a type of

power transmission that uses a gas and pressure

differential to create movement.

Commonly Air is used as fluid which is freely and

safely available.

COMPONENTS OF A PNEUMATIC

SYSTEM

• Compressor

• Regulators and Gauges

• Check Valve

• Buffer Tank or Accumulator

• Feed Lines

• Directional Valves

• Actuators

• Compressor

A compressor is a pump powered by an

electric motor. This pump compresses the air

to a higher Pressure. Compressors have a tank

to store the air. As a rule pneumatic

components are designed for a maximum

operating pressure of 8-10 bar but in practice it

is recommended to operate at between 5-6 bar.

Due to the pressure losses in the system the

compressor should deliver between 6.5-7 bar.

There are mainly 4 types of compressor

1) Centrifugal compressor

2) Rotary vane compressor

3) Rotary screw compressor

4) Reciprocating air compressor

• Pressure Regulator

Pressure Adjusting Knob *Pull out before turning

*Push in to lock

*Turn Clockwise

to Raise

Pressure.

Pressure Gauge 0-150 psi

0-1 MPa

Air Flow

Directional

Arrow

Lower Pressure Settings

Means Less Air Consumption

High Pressure

Inlet

Controlled Pressure Side

SYMBOLIC

REPRESENTATION

FRL UNIT (FILTER REGULATOR LUBRICATOR)

Sometimes in a pneumatic system there is a need to filter the air, monitor the air pressure or to lubricate the air for smooth running of the system. For this purpose FRL unit is used.

SYMBOLIC

REPRESENTATION

• Check Valve

Check valves are one-way valves

that are installed to the hose

connecting the compressor or

compressor tank to the buffer tank.

They allow the compressed air to

accumulate in the buffer tanks, but

do not allow backflow into the

compressor or compressor tank.

SYMBOLIC

REPRESENTATION

• Buffer Tank or Accumulator

Buffer tanks are secondary storage units for the compressed air originating

from the compressor. They store the high-Pressure compressed air for

eventual use with the pneumatic actuators. These tanks help to prevent

uneven airflow surges in the actuators; allow the compressor cycle to

maximize its shutoff timing; and allow the compressor to be kept at far

place from the actuators.

• Feed Lines

Feed lines are hoses that transfer pressurized air through the pneumatic

system. Large diameter hoses allow the pressurized air to travel quickly,

eliminating airflow backups.

The pipe diameter of the air distribution system should be selected in such a

way that the pressure loss from the pressurised reservoir to the consuming

device ideally does not exceed approx. 10 kPa (0.1 bar).

The selection of the pipe diameter is governed by:

1. Flow rate

2. Line length

3. Permissible pressure loss

4. Operating pressure

5. Number of flow control points in the line

• Directional Valves

Directional valves are placed before actuators. Multiple-valve

systems are installed on projects with multiple actuators to power.

Directional valves receive input from mechanical or electrical

control sources. They re-direct, stop or release the pressurized air to

its appropriate actuators at the times desired. Directional valves can

be triggered by the action of a button, spring, lever, pedal, solenoid

or other device. The different types of DVC are spool type, poppet

type, seat type etc.

Spool Valve:

A spool moves horizontally

with in the valve body to

control the flow of fluid.

POSITIONS OF A 5/2 DCV

A Solenoid Controlled 5 Ported, 4 Way 2 Position Valve

DS2_HLV_32_52_53_14.pdf

WORKING OF A SINGLE ACTING AND DOUBLE ACTING CYLINDER USING DCV

SINGLE ACTING CYLINDER

DOUBLE ACTING CYLINDER

• Valve switching positions are

represented as squares

• The number of squares shows how

many switching positions the valve has

• Lines indicate flow paths, arrows

shows the direction of flow

• Shut off positions are identified in the

boxes by lines drawn at right angles

• The connections (inlet & outlet ports)

are shown by lines on the outside of the

box

DIRECTIONAL CONTROL VALVES SYMBOL DEVELOPMENT

LIMIT SWITCHES

• Limit switches or valves are a type of position sensors. Limit valves uses a roller-lever actuator. This types of valves are available as a 3-way or a 5-way valve. This type of valve are normally actuated by a cylinder piston rod at the ends or limits of its extension of retraction stroke through physical contact.

3/2 valve

VALVE SYMBOL STRUCTURE


• The function of a valve is given by a pair of numerals

separated by a stroke, e.g. 3/2..

• The first numeral indicates the number of main ports.

These are inlets, outlets and exhausts but excludes signal

ports and external pilot feeds.

• The second numeral indicates the number of states the

valve can achieve.


• A 3/2 valve therefore has 3 ports (normally these are inlet,

outlet and exhaust) and 2 states (the normal state and the

operated state)

• The boxes are two pictures of the same valve

normal operated


• A valve symbol shows the pictures for each of the valve

states joined end to end

normal operated


• The port connections are shown to only one of the

diagrams to indicate the prevailing state

normal


• The operator for a particular state is illustrated against that

state

Operated state

produced by

pushing a button


• The operator for a particular state is illustrated against that

state

Operated state

produced by

pushing a button

Normal state

produced by

a spring


• The valve symbol can be visualised as moving to align one

state or another with the port connections


• A 5/2 valve symbol is constructed in a similar way. A picture of the valve flow paths for each of the two states is shown by the two boxes. The 5 ports are normally an inlet, 2 outlets and 2 exhausts


• The full symbol is then made by joining the two boxes and

adding operators. The connections are shown against only

the prevailing state


• The boxes can be joined at either end but the operator must be drawn against the state that it produces. The boxes can also be flipped

• A variety of symbol patterns are possible

normally

closed

normally

open


• The boxes can be joined at either end but the operator must be drawn against the state that it produces. The boxes can also be flipped

• A variety of symbol patterns can be produced

Reverse connected

VALVE FUNCTIONS

VALVE FUNCTIONS

Function 3/2

Normal position

Basic valves before

operators are added

Examples, push button operated

with spring return

Operated position

Function 5/2

OPERATORS

OPERATORS

General manual

Push button

Pull button

Push/pull button

Lever

Pedal

Treadle

Manual

Rotary knob

OPERATORS

Mechanical

Plunger

Spring normally

as a return

Roller

Uni-direction

or one way

trip

Pressure

Pilot pressure

Differential pressure

Detent in 3 positions

OPERATORS

Solenoid

direct

Solenoid pilot

Solenoid pilot

with manual override

and integral pilot

supply

Solenoid pilot

with manual

override and

external pilot

supply

Electrical

When no integral

or external pilot

supply is shown it

is assumed to be

integral

PORT MARKINGS

PORT MARKINGS

1

2 4

5 3

1

2

3

Push Button 3/2 Valve Spring Return

Push Button 5/2 Valve Spring Return

Actuators

An actuator is the component in a pneumatic system that does the work. There

are numerous types of actuators, powered by pressurized air. Plunge and

cylinder actuators are used frequently. The pressurized air is released into the

cylinder to move a piston forward as the air is forced into the chamber.

Examples of actuators at work are air-powered tools in construction and

dentistry.

Types of Actuator

Actuators may be grouped in a number of ways:

• Electromechanical

- Electromagnetic - The device has one coil which provides the field energy

and the energy to be transformed. The attractive force is unidirectional so a

return device of some type is needed, often a spring. Relays or solenoids are

used to switch - fans, head lights, horn, wipers.

- Electrodynamic - based on the (Lorenz) force generated when a current

carrying conductor (coil) is held in a magnetic field. - DC motors

• Fluid mechanical

- pneumatic. A common device is the pneumatic cylinder

- hydraulic. A common device is the hydraulic cylinder

The pneumatic cylinder has a significant role as a linear drive unit, due

to its

1. relatively low cost,

2. ease of installation,

3. simple and robust construction and

4. ready availability in various sizes and stroke lengths.

The pneumatic cylinder has the following general characteristics:

1. Diameters 2.5 to 320 mm

2. Stroke lengths 1 to 2000 mm

3. Available forces 2 to 45000 N at 6 bar

4. Piston speed 0.1 to 1.5 m/s

5. Single acting with return spring or Double acting

IMPORTANCE/ADVANTAGES OF PNEUMATIC CIRCUIT

• Pneumatics can be used for low cost industrial

applications – simple or complex.

• Welding and fabricating, press tools, automatic

machine tools, assembling, material handling, etc.

• Work function and control function is obtained by the

same power medium throughout the system

• Pneumatic circuits can be designed using number of

methods.

• Easy to expand once installed

DISADVANTAGES

• Initial weight and cost is high

• Requires fine tuning for optimum use

• Limited uses with larger actuators

• It produces noise due to the exhaust of air from the

system but can be eliminated by using mufflers

CONSTRUCTION OF PNEUMATIC CIRCUITS

SIMPLE PNEUMATIC CIRCUIT

PARTS OF PNEUMATIC SYSTE

• Compressor

• FRL Unit

• Direction control valve

• Actuator

• Cylinder

SPEED CONTROL PNEUMATIC CIRCUIT

• The motion of a double acting cylinder can be controlled by

using flow control valves.

TIME DELAY CIRCUIT

In certain engineering

applications, a predetermined

time delay may be required to

actuate a material handling

platform. At the end of the

extension stroke, the platform has

to wait for a predetermined time

for material removal and then it

has to return back.

PNEUMATICS CIRCUIT DESIGN METHODS USED BY ENGINEERS

1. Classic method – the method is based on the knowledge of pneumatic logic elements and application of the logics. (AND, NAND, OR, NOR, etc.)

2. Cascade method – the method is simple to apply and results in reliable and easily understood circuits.

3. Step-Counter method – A step counter is a digital modular counter, constructed from stepping units which serve as sequence steppers for asynchronous sequential fluid power controls

4. Logic design method (with Karnaugh- Vetch Maps) – a graphical design method using Karnaugh – Vetch maps is used to simplify intricate control problems and it produces the simplest possible result.

5. Combinational circuit design – combinational circuit output signals depend solely on the momentary state of their input signals or input variables. Its design tools are truth tables and Karnaugh Vetch maps.

CLASSIC METHOD

• Each pneumatic element is a

logic element performing

various logic functions like

AND, NAND, OR, NOR etc.

• The principle of Boolean

algebra and De Morgan

theorem are employed to solve

problems in the analysis of

control logics

THE FORWARD MOTION OF A SINGLE ACTING CYLINDER COULD

BE OPERATED FROM EITHER TWO LOCATIONS

• The pre condition is that the cylinder should operated from any of the two sources.

• Therefore A & B are signalling Elements and Y is the output. As per precondition

output signal is at Y so either A is NOT AND & B is YES OR or A is YES AND B

IS NOT.

• Then the control equation can be written as A . B + A . B = Y.

The logic diagram for this equation is as below

And type/

2-pressure

valve

CASCADE METHOD TO DESIGN PNEUMATIC CIRCUIT OF A MATERIAL

HANDLING EQUIPMENT

• Designing a pneumatic circuit for material handling using 3

cylinders.

• Step 1 – Extension and Retraction of the system is denoted by

+ & - signs, therefore A+, A-, B+, B-, C+ & C-

• Step 2 – the sequence should be split in minimum no. of

groups without repeating. So C-,A+,B+ & B-,A-,C+

• Step 3 – Number of pressure lines are equal to the number of

groups, so 2. number of group valve is number of groups

minus one, so 1 group valve. Cylinder actuating valve are

equal to the no. of cylinders.

ARRANGE THE PARTS OF PNEUMATIC CIRCUIT AS SHOWN

THE GROUP VALVE IS IN ITS LEFT-HAND POSITION, GROUP 1

IS PRESSURISED. LINE 1 IS CONNECTED DIRECTLY TO THE

PILOT LINE (-) OF CYLINDER ACTUATING VALVE VC

CYLINDER C RETRACTS AND THE LIMIT VALVE C0 IS

ACTUATED AND THE PRESSURE PASSES FROM MANIFOLD

LINE 1 THROUGH C0 TO THE PILOT LINE(+) OF CYLINDER

ACTUATING VALVE VA

CYLINDER A EXTENDS AND ACTUATES LIMIT VALVE A1 AND

PRESSURE PASSES FROM LINE 1 THROUGH A1 TO THE PILOT

LINE (+) OF THE CYLINDER VALVE VB.

B EXTENDS AND ACTUATES LIMIT VALVE B1. AS B+ IS THE

LAST STEP IN GROUP 1 NOW THE CONNECTION IS SHIFTED

BY CONNECTING TO THE PILOT LINE II OF THE GROUP

VALVE

LINE II IS CONNECTED TO THE (-) OF CYLINDER ACTUATING

VALVE VB, SO B RETRACTS AND VALVE B0 IS ACTUATED

PRESSURE PASSES THROUGH THE MANIFOLD LINE II TO THE

PILOT LINE (-) OF THE CYLINDER ACTUATING VALVE VA, SO

A RETRACTS AND ACTUATES LIMIT VALVE A0

THE PRESSURE PASSES FROM LINE II THROUGH A0 TO PILOT

LINE (+) OF CYLINDER ACTUATING VALVE VC, SO THE

CYLINDER C EXTENDS AND ACTUATES LIMIT VALVE C1 AND

THE PROCESS CONTINUES TILL THE SUPPLY IS STOPPED

CASCADE CIRCUIT

3.FLV

MATERIAL HANDLING EQUIPMENT

PNEUMATIC CIRCUIT FOR THE ABOVE MATERIAL HANDLING EQUIPMENT

USING CASCSDE METHOD

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87413621 pneumatics circuit

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