The document provides an overview of air compressors, detailing their types, operation principles, and applications in various industries. It covers positive displacement compressors, dynamic compressors, and specific types such as reciprocating, screw, and centrifugal compressors. The text concludes with references to further resources on air compressors and their integral role in industrial processes.

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AIR COMPRESSORS
Venu Manohar

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 Introduction.
 Types of compressors.
 Positive displacement compressors.
 Dynamic compressors.
 Reciprocating & screw compressors.
 Centrifugal compressors.
 Applications of compressors in industries.
 Conclusion & references.
Venu Manohar

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Principles on which compressors work:
 A compressor is a mechanical device that increases
the pressure of a gas by reducing its volume.
 Compressor is a machine which increases the
pressure of a fluid by mechanically decreasing its
volume (i.e. by compressing it).(The fluid here is
generally air since liquids are theoretically
incompressible).
 George Medhurst of England designed the first
motorized air compressor in 1799 and used it in
mining.
Introduction:

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Types of compressors:

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 In the positive-displacement type, a given quantity of
air or gas is trapped in a compression chamber and
the volume it occupies is mechanically reduced,
causing a corresponding rise in pressure prior to
discharge. At constant speed, the air flow remains
essentially constant with variations in discharge
pressure.
Ex: Reciprocating compressors, screw compressors, vane
compressors & so on.
Positive displacement compressor

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 Dynamic compressors impart velocity energy to
continuously flowing air or gas by means of impellers
rotating at very high speeds. The velocity energy is
changed into pressure energy both by the impellers
and the discharge volutes or diffusers. In the
centrifugal-type dynamic compressors, the shape of
the impeller blades determines the relationship
between air flow and the pressure (or head)
generate.
Ex: centrifugal compressors, axial compressors.
Dynamic compressors:

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Dynamic compressors

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 In a reciprocating compressor, a volume of gas is
drawn into a cylinder; it is trapped and compressed
by piston, then discharged into the discharge line.
The cylinder valves control the flow of gas through
the cylinder; these valves act as check valves.
Fig : of reciprocating compressor is as shown in next
slide.
Reciprocating compressors

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Principle of Operation

Fig shows single-acting piston actions in the
cylinder of a reciprocating compressor.

The piston is driven by a crank shaft via a
connecting rod.

At the top of the cylinder are a suction valve and a
discharge valve.

A reciprocating compressor usually has two, three,
four, or six cylinders in it.
Reciprocating compressors

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 The states of the refrigerant in a reciprocating compressor
can be expressed by four lines on a PV diagram as shown in
Fig
Reciprocating compressors
2
4
3
Clearanc
e
Discharge volume
Suction intake volume
Total cylinder volume
Piston displacement
volume
pressure

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Line 4-1:

The suction valve opens at point 4.

As the piston travels toward the bottom dead
center, the volume of the cylinder increases and the
vapor flows into the cylinder.

The pressure inside the cylinder is slightly less than
suction line pressure. The pressure difference
pushes the valve open on during the suction
stroke.
Reciprocating compressors

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Line 2-3:

At point 2, the pressure inside the cylinder has
become slightly greater than discharge line
pressure.

This causes the valve opening allowing the gas to
flow out of the cylinder.

The volume continues to decrease toward point 3,
maintaining a sufficient pressure difference across
the discharge valve to hold it open.
Reciprocating compressors

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Line 3-4:

At point 3, the piston reaches the top dead center and reverses
direction.

At top dead center, as the piston comes to a complete stop prior
to reversing direction, the pressure across the valve is equal.

So, the discharge valve is closed.

As the piston moves towards point 4, the volume increases and
the pressure decreases in the cylinder.

The gas trapped in the cylinder expands as the volume increases
until to point 4.

At point 4, the gas pressure inside the cylinder becomes less than
the suction line pressure, so the suction valve opens again.

The cycle then starts over again.

The shape of the re-expansion line (Line 3-4) is dependent on the
same compression exponent that determines the shape of the
compression line.
Reciprocating compressors

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Reciprocating compressors

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 Screw compressors are also belong to the positive
displacement compressor family.
 In screw compressors, the compression is
accomplished by the enmeshing of two mating
helically grooved rotors suitably housed in a cylinder
equipped with appropriated inlet and discharge
ports
 The rotors are the main components of the screw
compressor.
 A cross view of the two principle rotating elements of
the screw compressor is shown
Screw compressors

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 The male rotor is normally the driving rotor and
consists of a series of lobes (usually four) along the
length of the rotor that mesh with similarly formed
corresponding helical flutes (usually six) on the
female rotor.
Screw compressors

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 As the rotors turn, gas is drawn through the inlet
opening to fill the space between the male lobe and
the female flute.
 As the rotors continue to rotate, the gas is moved
past the suction port and sealed in the inter-lobe
space.
 The gas so trapped in the inter-lobe space is moved
both axially and radially and is compressed by direct
volume reduction as the enmeshing of the lobes
progressively reduced the space occupied by the gas.
Screw compressors

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Screw compressors

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Screw compressors

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 Screw compressors are reliable and compact.
 Compressor rotors can be manufactured with very
small clearances at an economic cost.
 The absence of reciprocating inertial forces allows
the screw compressor to run at high speeds. So, it
could be constructed more compact.
 The continuous flow of cooling lubricant allows much
higher single-stage compression ratios.
Advantages of screw compressors

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 Rotary vane compressors consist of a rotor with a
number of blades inserted in radial slots in the rotor.
The rotor is mounted offset in a larger housing that
is either circular or a more complex shape. As the
rotor turns, blades slide in and out of the slots
keeping contact with the outer wall of the housing.
Thus, a series of decreasing volumes is created by
the rotating blades.
Rotary vane compressors

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Rotary vane compressor
 A: Air is drawn in through the intake valve.
B: Air is contained between the rotor and stator wall.
C: Air is compressed by decreasing volume.
D: High pressure air passes into the primary oil separator.
E: Remaining traces of oil are removed in a final separator element, providing high quality
air.
F: System air passes through the after cooler, removing most of the condensate.
G: Oil is circulated by internal air pressure. It passes through an air-blast oil cooler and
filter before being returned to the compressor.
H: Air flow is regulated by an inbuilt modulation system.

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 A scroll compressor (also called spiral compressor, is
a device for compressing air or refrigerant. It is used
in air conditioning equipment.
Scroll compressor

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 These devices are known for operating more
smoothly, quietly, and reliably than conventional
compressors .
 The absence of pistons for gas compression enables
scroll compressors to reach 100% volumetric
efficiency, leading to reduced energy costs.
 Their weight and footprint are considerably smaller
compared to other bulkier types of compressors.
 scroll compressors have been used food and fruit
refrigeration, truck transportation, marine containers
air-conditioning applications.
Advantages of scroll compressor & applications

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Lobe compressors
Lobe compressors are used in water treatment for
backwashing of filter beds.
 Effluent treatment for diffused aeration & agitation
of effluents.
 Aquaculture: For maintaining dissolved oxygen
levels.

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 The centrifugal air compressor is a dynamic
compressor, which depends on transfer of energy
from a rotating impeller to the air. The rotor
accomplishes this by changing the momentum and
pressure of the air. This momentum is converted to
useful pressure by slowing the air down in a
stationary diffuser.
Centrifugal compressors

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Centrifugal compressors

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Centrifugal compressors

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 Centrifugal compressors are used throughout
industry because they have fewer rubbing parts, are
relatively energy efficient, and give higher airflow
than a similarly sized reciprocating compressors or
positive-displacement compressor.
 Centrifugal compressors are often used in small gas
turbines engines and smaller aircraft gas turbines.
 It can reach up to pressure of 1200 psi.
 It has high efficiencies when compared to
reciprocating compressors.
Advantages of centrifugal compressors

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 Reciprocating compressors are typically used where
high compression ratios (ratio of discharge to suction
pressures) are required per stage without high flow
rates, and the process fluid is relatively dry.
 Screw compressors: Trailer mounted diesel powered
units are often seen at construction sites, and are
used to power air operated construction machinery.
Application of compressors

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Application of compressors
 P.E.T bottling industries, gas filling stations usually
use reciprocating compressors.
 Processing equipment, Oxygen Generators Oil
Atomization use compressors of required capacity.

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 Air compressors: a compressor that takes in air at
atmospheric pressure and delivers it at a higher
pressure.
 Compressors serve the basic necessities & form an
integral part of the company .
References:
 www.engineeringtoolbox.com/air-compressor.
 en.wikipedia.org/wiki/Gas compressor.
 Hydraulics & pneumatics – Anthony Esposito.
 http://en.wikipedia.org/wiki/Rotary_screw_compressor.
Conclusions & references

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