reciprocating air compressors

concretecakeUrban and Civil

Nov 29, 2013 (3 years and 9 months ago)

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RECIPROCATING


AIR COMPRESSORS

By

Mr. Manoj Kumar Elipey

Assistant professor

Vardhaman College Of Engineering


Air

composer

is

a

machine,

which

increases

pressure

of

air

and

delivers

it

at

required

pressure
.

An

air

compressor

takes

air

from

atmosphere,

compresses

it

and

delivers

the

high

pressure

air

to

a

storage

vessel

from

which

it

may

be

conveyed

by

the

pipe

line

to

wherever

the

supply

of

compressed

air

is

required
.


Compressor

is

driven

by

some

form

of

prime

mover,

work

should

be

done

upon

the

gas
.

Of

the

energy

received

by

the

compressor

from

the

prime

mover,

some

will

be

absorbed

in

work

done

against

friction,

some

will

be

lost

to

radiation

and

any

coolant

which

might

be

employed

to

cool

the

machine,

and

the

rest

will

be

maintained

the

air

itself
.

Applications

of

compressed

air





1
)

For

spray

painting

in

automobile

industry
.



2
)

To

operate

air

brakes

in

automobiles,


pneumatic

conveyers
.



3
)

Air

condition

applications
.



4
)

In

blast

furnaces
.



5
)In

aeroplane

application


(Axial

air

compressors)
.



6
)

To

supercharge

IC

engines
.



7
)

Filling

tyres

in

automobile

tyres
.



8
)

For

driving

mining

tools
.



9
)

For

convey

materials

like

concrete,

sand

along


pipelines
.

Types

of

compressors


Depending

on

the

design

and

principle

of

operation,

compressors

are

broadly

divided

into

two

types
.


1
)

Reciprocating

compressors


2
)

Rotary

compressors


Reciprocating

compressors



It

is

a

positive

displacement

compressor

in

which

the

pressure

is

carried

out

by

containing

air

between

the

cylinder

walls

and

the

piston

and

reducing

the

volume

by

the

movement

of

the

piston
.

These

are

used

where

high

pressures

are

required
.

Rotary

compressors



The

compression

is

achieved

by

revolution

of

a

rotor

about

its

axis
.

These

are

used

where

large

volume

of

air

at

medium

pressure

is

required
.


These

are

divided

into

2

types



1
)

positive

displacement

type

compressor
.



2
)

Dynamic

type

rotary

compressor
.


In

positive

displacement

type

rotary

air

compressor

the

air

is

trapped

in

the

space

between

two

surfaces
.



for

example

:







Screw

compressor
.





Roots

blower
.





Vane

blower
.


In

dynamic

type

rotary

compressor

air

is

compressed

by

dynamic

action

of

the

rotating

blades

or

vanes

which

accelerated

and

compresses

the

air
.



for

example

:







1
)

centrifugal

compressor
.


Air

enters

axially

and

leaves

radially,



It

is

also

called

as

radial

compressor





2
)

Axial

flow

compressor
.


Air

enters

axially

and

leaves

axially
.

Classification

of

Reciprocating

compressor



A)

Depending

on

the

operation



1
)

Single

acting

compressor
.



2
)

Double

acting

compressor
.


B)

Depending

on

the

number

of

stages



1
)

Single

Stage
.



2
)

Multi

Stage
.





C)

Method

of

cooling



1
)

Air

cooled

compressors
.



2
)

Water

cooled

compressors
.

η

vol = actual volume of air drawn per stroke at NTP/


Stroke volume

Volumetric efficiency is defined as the ratio of actual volume
of air drawn per stroke at NTP to piston displacement.


η

mech

:



It

is

defined

as

ratio

of

indicated

power

of


the

compressor

to

the

brake

power
.

η

isothermal

=



Isothermal

efficiency

defined

as

the

ratio

of

isothermal

power

to

the

indicator

power
.

η

overall =



The ratio of the isothermal power of
the compressor to the shaft .

Advantages

of

multistage

compression
.


1
)

Air

can

be

cooled

at

intermediate



pressures
.


2
)

Power

required

to

run

multistage

compression

is



less

than

single

stage

compression
.


3
)

Multistage

compressors

have

less

fluctuations


4
)

Volumetric

efficiency

is

more
.


5
)

Improved

lubrication

due

to

low

temperature
.



Disadvantages

of

Multistage

compression
.




1
)

The

initial

cost

is

high

as

intercooler

is

likely

to

be



more

expensive
.