reading materials on fundamentals of pneumatics

Prepared by Hydraulics & Pneumatics Lab., HRD Centre Page #1 of 1

READING MATERIALS

ON

FUNDAMENTALS OF PNEUMATICS

STEEL AUTHORITY OF INDIA LIMITED

ROURKELA STEEL PLANT

HUMAN RESOURCE DEVELOPMENT CENTRE

SAIL, Rourkela Steel Plant, Rourkela Page #2 of 2

Introduction to pneumatics

Pneumatic power (Air power) based control system & equipments are now increasingly used.

New development is taking place in the control technology & automation, In recent years

compressed air has been applied to control circuitry, dental and surgery applications as well as in

many industrial processes requiring high forces or impact blows. The pneumatics is also applied to

lifts in automobile service stations.

Some of the industrial applications of compressed air are:-

Air brake: Locomotives and automobiles

Air cylinder: for linear movements of load attached to them,

Or lifting, lowering, transferring and positioning load

Air motor: For rotary movement to rotate the load attached to them.

Paint spray

Process control

Conveying

Transferring

Forming

Pressing

Forging

Pneumatics tools: Drilling, chipping, Reaming, Grinding, Screw Driving Rivetting.

There are still many applications of pneumatics.

ADVANTAGES OF PNEUMATICS POWER SOURCE

Fairly cheap ( air is freely available in nature)

Convenient transmitter of power.

Pipes (fluid lines) and connectors- easy to handle.


Leaky joints do not create a house keeping problem.

Exhaust is easy.

Cleaner system.

Non flammable.

Suitable for speedy operations

SOME DISAVANTAGES

Air is compressible.

System is affected by altitudes (compressor capacity)

It cannot be used for high pressure working.

Air is noisy.

Liquids in the line are harmful for the system.

Equipment is bulky high force applications.

COMPONENTS OF APNEUMATIC SYSTEM

A pneumatic system consist of :-

Generating unit:(compressed air source) Generates compressed air for the system. It is

known as compressor. It raises air pressure from atmospheric to the required system pressure.

Compressor sucks air from atmosphere, compresses and discharges it in to the receiver tank,

where the pressure is built up for use.

Air drier : It drive the compressed air. Compressed air consists of liquid vapour and

condensates. These liquid contaminants are to be removed before feeding to the system to

protect the system from rusting and varnishing.

Driers are needed – when the system requires dry air.

Filter, Regulator and Lubricator (FRL, unit): This is the most important component of the

system. This unit provides clean, regulated and lubricated air to other parts of the system.

Lubricator is eliminated when only clean dry air is required to the system. Which do not require

lubrication, components are pre lubricated .


Controls:- These components control the pressure in the system, speed and direction of

actuation movement.

These are pressure , direction and flow control valves.

Actuators :- These are the main working components on which load is attached.

In actuators kinetic energy of compressed air is converted in to mechanical energy. Linear

or rotary motions can be obtained depending on the type of actuators.

Out of the above the following items have been discussed in detail. Since the other parts

are the similar to those used in hydraulic systems and have been dealt in detail in hydraulic

section, they have been left at this moment.

1. Air filter

2. Regulator

3. Lubricator

4. Pressure switch

5. Safety relief valve

AIR FILTER

Air filter is one of the most important component of a pneumatic system. Proper size and rating of

filter are to be selected for the desired flow and filtration level and also filters are to be maintained

properly for their efficient functioning.

The main function of the air filter is to remove foreign matter moisture, pipe scales, dirt etc from

the air and allow clean dry air to flow without restriction, to inlet of the pneumatic system. Air filter

protects the pneumatic system and prolongs its service life.

TYPE OF AIR FILTERS

INTAKE FILTER:-


Intake filters are generally of felt or cotton wool impregnated with fine wire mish filter elements.

These are fitted on the intake (suction) line of the compressors.

Intake filters are the first line defense of the pneumatic system. These filters removes particles and

dust at the intake of the compressor and protects the early failure.

AIR LINE FILTER:

An air line filter is a device that is placed in the air line at the work station that is to be protected

from contaminants. It removes particulate matter (fine dust and liquid contaminants) from the air

passing through the filter element. It cannot remove vapors of moisture or oil.

COMPONENTS OF AIR LINE FILTER:

Housing

Inlet and outlet ports

Deflector plate

Shroud

Filter element

Baffle plate

Filter bowl

Drain (manual or automatic)

WORKING OF AIR LINE FILTER

The air line filter works by forcing the incoming air flow through a deflector or shroud,

imparting a centrifugal action, forces heavier contaminants port. The air continues to pass through

filter elements leaving behind the particles unable to pass through the force of the elements.

Filtered air leaves through the discharge port into the pressure regulator of the system and further.

FILTER ELEMENT MATERIALS:

Filter elements for industrial air line filter are 40 micron (COARSE) to 5 micron (fine) average hole

size (nominal size)


CLASSIFICATION OF FILTER ELEMENTS:

Elements are classified in two groups:

1. Depth type (s bronze and some plastics)

2. Edge (surface) type (resin impregnated paper wound ribbon type)

DEPTH TYPE ELEMENTS:

The Depth type element traps dirt in torturous path away inside as air travels from inlet to outlet

port through filter element.

An advantage of the depth type is that long fibers of diameters small enough to get in can be

trapped by torturous path. Penetration is more difficult.

EDGE TYPE ELEMENT:

Edge type element traps the dirt outside and builds up a dirt cake. It has selectively straight flow

path.

SERVICING OF ELEMENT:

Servicing of element depends on the pressure drop across the filter. Excessive pressure drop may

collapse textile or felt type element. Porous bronze can be cleaned by back flushing (applying the

air pressure in the reverse direction). A limit of three cleanings is recommended before replacing

porous bronze elements for best performance. Other elements must be disposed off. The pressure

drop of 10 PSI (a differential pressure of 10 PSI) is the indication of the time for servicing filter

element.

PRESSURE REGULATORS

In pneumatic system local demand fluctuation can cause system pressure drops or variation, as a

result the actuators (cylinders or motors) speeds vary i.e may becomes slow or fast. This is not

desirable in any production operation.


Hence the air delivered to the work point is often higher than needed to overcome the local

demand fluctuation .To control the machine forces and to save air it is necessary to reduce the air

pressure and to prevent fluctuation caused by compressor cycling between its higher and lower

pressure setting.

Reduced pressure is supplied to the system by a unit known as a pressure regulator. It is located at

the point of use.

It may be combined with a filter unit or a separate unit is fitted after air filter or in the leg of the

circuit where pressure regulator is needed. The pressure regulator is equipped with the tube

pressure gauge.

FUNCTION OF A REGULATOR

It delivers output (secondary) air at constant preset pressure regardless of pressure variations from

the compressor and independent of flow.


It reduces the pressure to a level to meet the work requirement (pressure set by an adjusting

screw)

It reduces wastage of compressed air energy and saves operation cost.

1.Adjusting screw

2. Regulator screw

AIR LINE LUBRICATOR

Proper lubrication is necessary to coat the resilient scale to reduce friction and significantly

extend their life. Most pneumatic cylinders and motors also require lubrication to reduce friction,

prevent scoring and thus to increases the life of the motor or cylinder, proper lubricant of

controlled quantity render good lubrication excess lubrication amount be avoided for proper

functioning of the system.

Remember , oil put into the system must be taken out (remove) before the air is returned to the

atmosphere.

The safety and health regulations does not permit more than 5 mg of oil mist particles per cubic

meter of exhaust air.

oil removal filter may be used to remove oil in the exhaust air if it goes beyond 5mg/cu. m of air.

It is most important that the lubricators must be refilled at regular intervals and check the

lubricator for proper functioning. The defective lubricator must be repaired or replaced as early as

possible.

FUNCTIONS OF LUBRICATORS:

Deliberate lubrication can be provided by periodic inspection of oil through an extra port by drip

type oiler or by automated pressure injection of the lubricant.

Most common today is the introduction oil droplets into the air supply by air line lubricators. The

lubricant may be in the form of drops, spray or mist in the following air. It is common to place filter,

regulator and lubricator in the unit.


PRESSURE SWITCH

A common way of sensing tank pressure and controlling actuation and de actuation of a relatively

small (5-10 HP) compressor is with a pressure switch. Large compressors use other means of

various types.


SAFETY RELIEF VALVE

However maximum pressure developed by a compressor is designed to be regulated by a

control system Which senses discharge or tank pressure. In case of an emergency, as in the failure

of a control system to function properly, appositive displacement compressor system should have a

safety relief valve. This is maintained by law for most applications.

A safety relief valve consists of a valve body with inlet and exhaust passages and internal

moving part. In the lubrication the moving part is a poppet which is held biased in one position by

spring . to comply with safety codes the valve will have a manual test lever .


GRAPHICAL SYMBOLS


hh


ff


gg

reading materials on fundamentals of pneumatics

Documents