Unit:V

Pneumatics

IntroductionPneumatics is application of compressed air

(pressurized air) to power machine or control or

regulate machines.

Defined as the branch of fluid power technology that

deals with generation, transmission and control of

power using pressurized air.

Any gas can be used in pneumatic system but air is the

most usual . Pure nitrogen may be used if there is a

danger of combustion in a work environment.

Compressed air is used as the working medium,

normally at a pressure from 6 bar to 8 bar.

Using Pneumatic Control, maximum force up to 50 kN

can be developed.

Choice Of Working Medium and System.

When the system requirement is-1. high speed, medium pressure (usually 6 to 8 bar) and less

accuracy of position, then pneumatic system is preferred.

2.high pressure and high precision, a fluid system with oil is good.

3.power requirement is high like in forging presses, sheet metal

press, it is impossible to use air system. Oil hydraulics is the only

choice

3.Air is used where quick response of actuator is required.

4.If the application requires only a medium pressure and high

positional accuracy is required then hydro –pneumatic system is

preferred

5. Air is non-explosive, it is preferred where fire/electric hazard are

expected.

Oil systems are more prone to fire and electrical hazards and are

not recommended in such applications.

Industrial applications of Pneumatics-

1. Material handling

2. Clamping

3. Shifting

4. Positioning

5. Branching of material flow

6. Packaging

7. Filling

8. Transfer of materials

9. Sorting of parts

10. Stamping and embossing of components

Industrial processes

1.Drilling

2.Turning

3.Milling

4.Sawing

5.Finishing

6.Forming

A Pneumatic machine is used

to dismantle an automobile

tire

A heavy duty pneumatic Jackhammer

A pneumatic machine is

used in an Automobile

painting

A Dental drill is one of the

uses of the pneumatic

technology

Advantages of Pneumatics-1- Availability: Air is available everywhere in unlimited

quantities.

2- Transport: Air can be easily transported in pipelines,

even over large distances.

3-Storage: Compressed air can be stored in a

reservoir/tank and removed as required.

4- Temperature: Compressed air is relatively insensitive

to temperature fluctuations.

5- Cleanliness: Unlubricated exhaust air is clean.

6- The running cost is relatively inexpensive

7-Speed: Compressed air is a very fast working medium.

This enables high working speeds to be attained.

8-Overload safe: Pneumatic tools and operating

components can be loaded to the point of stopping and

are therefore overload safe.

Disadvantages-1-Preparation: Compressed air requires good

preparation. Dirt and condensates should be removed.

2- Speed: As air is compressible; it is difficult to achieve

uniform and constant piston speed.

3- Force requirement: Compressed air is economical

only up to a certain force requirement. Under the

normal working pressure of 600 to 700 kPa (6 to 7 bar).

4- Noise level: The exhaust air is loud (noise). This

problem has now, however been largely solved due to

the development of sound absorption material and

silencers.

5.Lubrication

6.Low thermal conductivity

Industrial compressed air system.

Preparation of the compressed air:The following points should be considered in preparing

compressed air plants:

1. Quantity of air required to meet the demand of the

system

2. Type of compressor to be used to produce the quantity

required

3. Pressure requirements

4. Storage requirements

5. Requirements for air cleanliness

6. Acceptable humidity levels to reduce corrosion and sticky

operation

7. Lubrication requirements, if necessary

8. Temperature of the air and effects on the system

9. Line sizes and valve sizes to meet demand

10. Material selection to meet environmental and system

requirements

11. Drainage points and exhaust outlets in the distribution

system

12. Layout of the distribution system to meet demand.

Absolute pressure = Atmospheric pressure + Gauge pressure.

Gas Laws/ Laws of compression:

1.Boyle’s Law:

“If a given mass of a gas is compressed or

expanded at a constant temperature, then the

absolute pressure is inversely proportional to

the volume”.

2.Charles law:

If a given mass of a gas is heated or cooled at

a constant pressure, then the volume is

directly proportional to the absolute

temperature.

3.Gay-Lussac’s Law :

“At constant pressure, the absolute pressure

of an ideal gas will vary directly with the

absolute temperature.”

Compressors can be classified in the

following different ways.

(a)Based on principle of operation:

(i) Positive displacement compressor.

(ii) Non-positive(Dynamic) displacement

compressors.

ISO symbol of air compressor

Positive displacement compressors can be

further classified based on the type of mechanism

used for compression.

A) Reciprocating type positive displacement

compressors

I. Single acting

II. Double acting

III. Diaphragm

B) Rotary type positive displacement compressors.I. Roots blower

II. Vane type compressors

III. Lobe

IV. Scroll

V. Screw

RECIPROCATING COMPRESSORS

1.PISTON COMPRESSORS

A. SINGLE ACTING CYLINDER COMPRESSOR

WORK DONE IN A SINGLE STAGE COMPRESSOR CONSIDERING CLEARANCE.

B. DOUBLE ACTING CYLINDER COMPRESSOR

It is development of single acting compressor

Both sides of piston are used to compression process

Diaphragm compressors

Rotary type positive displacement compressors

Scroll compressor

Source of contamination.

The quality of air being drawn into the compressor-

atmosphere containing large numbers of airborne

contaminants.

The type and operation of the air compressor-

from wear particles come with coolants and lubricants

Compressed air storage devices and distribution

systems-

air receiver and system piping will also store the large

amounts of contaminants which drawn into the system.

Types of contamination in a compressed air system

1.Atmospheric dirt:

Atmospheric air in an industrial environment

typically contains 140 million per m3 of dirt

particles. 80% of these particles are less than 2

microns in size and are too small to be captured by

the compressor intake filter, therefore passing directly

into the compressed air system

2.Water vapour, condensed water

3.Liquid oil :

oil mixes with water vapour in the air and is often

very acidic, causing damage to the compressed air

storage and distribution system, production

equipment and final product.

CONDITIONING AND DISTRIBUTION OF

COMPRESSED AIR :

The purpose of the fluid conditioners is to make the

compressed air more acceptable and suitable fluid

medium for the pneumatic system as well as the

operating personal.

The following fluid conditioners are used in pneumatic

systems

1. Air Filters

2. Air Regulators

3. Air Lubricator

AIR FILTERS:

Function of air filters:

1. To remove all foreign matter and allow dry and clean air

flow without restriction to regulator and then to the

lubricator

2. To condensate and remove water from the air

3. To arrest fine particles and all solid contaminants from

air

Filters are available in wide range starting from a fine

mesh wire cloth (which strains heavy foreign particles) to

elements made of synthetic material (which removes very

small particles)

Usually in line filter elements can remove contaminants

in the 5-50 micron range.

Construction of typical cartridge type filter:

Filter bowl is usually made of plastic and transparent.

For pressure more than 10 bar, bowl may be made of brass.

The pressure difference between inlet

and outlet will indicate the degree to

which the filter element is clogged.

Commercially available filters have

many additional features like automatic

drain facility, service life indicator etc.

Factor affecting selection of filters

1. Size of particles to be filtered from

the system

2. Capacity of the filter

3. Accessibility and maintainability

4. Life of the filter

5. Ability to drain the condensate

AIR REGULATOR:

Function:

The function of the air pressure regulator is to maintain

working pressure virtually constant regardless of

fluctuations of the line pressure and air consumption.

When the pressure is too low, it results in poor

efficiencies and when the pressure is too high, energy is

wasted and equipment’s performance decay faster.

Where to regulate?

Generally pressure is regulated in pneumatic system

at two places.

1. At the receiver tank-required as a safety measure

for the system

2.In the load circuits-to regulate the pressure for

downstream components such as valves and

actuators.

Types of Pressure regulator

1.Diaphragm type

regulator

2. Piston type regulator

1.Diaphragm type regulator is commonly

used in Industrial pneumatic system.

Relieving or Venting Type Pressure regulator

AIR LUBRICATOR:

Function: The function of air lubricator is to add a

controlled amount of oil with air to ensure proper

lubrication of internal moving parts of pneumatic

components.

Lubricants are used to

1. To reduce the wear of the moving parts

2. Reduce the frictional losses

3. Protect the equipment form corrosion

Excessive lubrication is undesirable. Excessive

lubrication may results in

1. malfunctioning of components,

2. seizing and sticking of components after prolonged

downtime

3. environmental pollution

Filter Regulator Lubricator Unit (FRL Unit) /Service Unit

Pneumatic Dryers

PNEUMATICS ACTUATORS:

1. Pneumatic actuators are the devices used for

converting pressure energy of compressed air

into the mechanical energy to perform useful

work.

2. Actuators are used to perform the task of exerting

the required force at the end of the stroke or

used to create displacement by the movement of the

piston..

3. The pressurised air from storage is supplied to

pneumatic actuator to do work.

TYPES OF PNEUMATICS ACTUATORS

1. Linear Actuator or Pneumatic cylinders

2. Rotary Actuator or Air motors

3. Limited angle Actuators

Types of Pneumatic cylinders /Linear

actuators

1.Based on application for which air

cylinders are used

i) Light duty air cylinders

ii) Medium duty air cylinders

iii) Heavy duty air cylinders

2. Based on the cylinder action

i) Single acting cylinder

ii) Double acting cylinder

a. Single rod type double acting cylinder

b. Double rod type double acting cylinder

3. Based on cylinder’s movement

i) Rotating type air cylinder

ii) Non rotating type air cylinder

4. Based on the cylinder’s design

1. Telescopic cylinder

2. Tandem cylinder

3. Rod less cylinder

I.Cable cylinder,

II. Sealing band Cylinder with slotted cylinder barrel

III. Cylinder with Magnetically Coupled Slide

4.Impact cylinder

5.Duplex cylinders

6.Cylinders with sensors

Based on the cylinder action

A) Single acting cylinders.

There are varying designs of single acting cylinders

including:

1. Diaphragm cylinder

2. Rolling diaphragm cylinder

3. Gravity return single acting cylinder

4. Spring return single acting cylinder

Diaphragm cylinder:piston is replaced by a diaphragm is replaced by a diaphragm

of hard rubber,plastic or metal clamped between the two halves of a metal casing expanded to form a wide, flat enclosure

Rolling diaphragm cylinder :They are similar to diaphragm cylinders.

They too contain a diaphragm instead of piston, which is this

instance rolls out along the inner walls of the cylinder when air

pressure is applied to the device, thereby causing the operating

stem to move outwards.

Compared with the standard diaphragm type, a rolling diaphragm

cylinder is capable of executing appreciably longer operating

strokes (averaging from 50 mm to 800mm) .

Gravity Return Single Acting Cylinder

Double acting cylinders.

Telescopic Cylinder

Cable cylinder:

•It is used for very long strokes, up to 2000mm.

• It consists of nylon jacketed cable which enters the cylinder

barrel and is attached to one end of internal cylinder and exits

through the gland seal and enters into the other end of the

internal cylinder through the another gland seal.

• When compressed air enters the cylinder the piston moves from

end-to-end.

Cylinder with Magnetically Coupled Slide

The magnetic cylinders are available upto the size of about 40

mm diameter and stroke lengths from 50mm to 4000 mm.

They can operate at the speed of about 3000 mm/sec.

The major advantages of this type of cylinders are

i) There is no leakage

ii) There is no direct contact of moving elements therefore the

wear is less

iii) The orientation of the carriage can be changed easily,

Position sensor for cylinders

Cylinder mountings.