The document provides an overview of air compressors, defining them as machines that compress air or gas from low to high pressure. It discusses various types of compressors, including reciprocating, rotary, and multistage compressors, along with their operational principles, advantages, and efficiency metrics. Additionally, it covers specific applications of compressed air across different industries and explains key concepts such as indicated power, brake power, and volumetric efficiency.

1. TOPICS: AIR COMPRESSOR
Prepared by:
BABARIYA SHANIKUMAR SANJAYBHAI : 130110120005
BAGADA RAVIKUMAR : 130110120006
BHARADAVA RAVI MANSUKHBHAI : 130110120007
BHAVSAR HEMDEEP RASHMIKANT : 130110120008
Respected Faculty:
Prof. Saurin M. Sheth
College : G. H. Patel college of engineering & technology
Branch : Mechatronics (2nd sem)

2. WHAT IS AIR COMPRESSORS?
COMPRESSOR :
“The machine which takes in air or any other gas at low pressure
and compresses it to high pressure are called compressors.”
The compressor used for increasing the pressure is called “air
compressor.”

3. USES OF COMPRESSED AIR
 In refrigeration cycle.
 Operating tools like drill, hammers etc.
 Filling the air in automobile tires.
 Spray painting.
 Pumping of water.
 Gas turbine power plant.
 Conveying the materials like sand and concrete along the pipe
line.
 Sand blasting
 Operating blast furnace
 To operate air motor in mines where is high fire risk.

5. RECIPROCATING COMPRESSORS
 This compressors are widely used for compressing air for all
range of pressure.
 Construction:
 It consists if the cylinder in which a piston reciprocates.
 Piston is driven by crank connecting rod.
 The crank is mounted in crankcase.
 The valve are generally pressure differential type.
 Thus they operate automatically by the difference of the pressure
across the valve.

6. OPERATIONS OF A COMPRESSOR
Operation without clearance :
 It is assumed that in an ideal compressor there is no
clearance volume at the end of the stroke.
 In this type compressor, when piston is moving away from
TDS, pressure inside cylinder will decrease and volume will
increase. Hence pressure difference across the valve is
created.
 The spring operated inlet valve will be opened automatically.
 Therefore atmospheric air enters into cylinder at constant
pressure p1 with increase in volume.
 The piston moves towards the TDS from BDC during the
second stroke.

7. P
P2 3 2” 2’ 2
P1 4 1
V1 V

8.  The air is compressed adiabatically with increase pressure (as
shown in curve {1-2}.)
 When the pressure of compressed air becomes equal to the
pressure of receiver in which the air is delivered, the spring
operated delivery valve opens automatically and the air is
forced into the receiver at constant pressure P2 from the
cylinder.
 This process is shown by the horizontal line (2-3).
 Again the piston moves away from TDS. Thus, the cycle is
completed and the same cycle will be repeated.
 The area of the diagram (1-2-3-4) represents the work
required to compress the air from pressure P1 to P2 for
adiabatic compression.

10. Operation with clearance :
 Clearance Volume required because of
 Preventing striking of piston at cylinder head
 Thermal expansion due to high temperature at the end of
compression
 Maintaining machine tolerance.
 In the graph clearance volume is denoted by V3 or Vc.
 The residual compressed air at pressure p2=p3 is filled in
clearance volume at the end of upward stroke of piston.
 During the suction stroke this compressed air expands and it is
denoted by the curve (3-4) on p-V diagram.
 This expansion will reduce the pressure from p2=p3 to intake
pressure p4=p1 and inlet valve will begin to open and permit the
intake of a fresh air.

11. The volume (v1-V4) is known as suction volume or
effective swept volume or free air delivery at
suction condition.
The effect of clearance is to reduce the volume of
air actually sucked in per working cycle.
P
P2=P3
P1=P4

12.  Indicate power:
 The power required to compress the air is called the indicated
power or cycle power or air power.
 Brake Power :
 The power required to drive the compressor is called the brake
power or shaft power of compressor.
 B.P = 2πNT / 60000
 Where N= Compressor speed, RPM
 T= Torque, Nm
 For compressor the B.P is greater than I.P .

13.  Mean effective pressure (pm):
 For compressor it is calculated by work done per cycle.
 Work done/ cycle = pmLA,
 Where LA= swept volume m3/cycle.
 Pm = {n/n-1x p1
(v1
-v4
)x[(p2
/p1
)n-1/n
– 1]} /Vs
 Mechanical efficiency :
 The ratio of indicated power to the brake power of compressor is
called mechanical efficiency.
 nm =

14.  Isothermal efficiency:
 It is defined as the ratio of isothermal work to indicate work.
 niso = Isothermal work / Indicated work
 niso = p1V1loge (p2/p1)
(n/n-1)p1V1 [(p2/p1)n-1/n -1 ]
 Volumetric efficiency(nv):
 It is the ratio of effective swept volume to swept volume of
cylinder.
 nv= 1-C[(p2/p1)1/n – 1]
 From above eqn , volumetric efficiency reduces with the
increase in pressure ratio and clearance ratio C.

15. MULTISTAGE RECIPROCATING COMPRESSOR
 Process:

16.  ADVANTAGES:
1. Without intercooling, the curve of compression will follow the
path (1-4”),hence the saving in work input due to inter cooling.
2. Less shaft power is required for a given pressure ratio due to
the saving in work input.
3. Due to smaller working temperature, better lubricating effect is
provided.
4. Better mechanical balance and smooth torque-angle diagram is
obtained.
5. Less leakage problems due to less pressure difference for each
stage.

17. ROTARY COMPRESSORS
Rotary
Rotodynamic
Centrifugal
Axial flow
Positive
Roots
blower
Screw blower
or
compressor
Vane type
blower

18. CENTRIFUGAL COMPRESSORS

19.  It is consist of a impeller and a volute casting.
 Due to rotation of the impeller at high speed produces the
centrifugal force which cause the air to move out of the
impeller at a higher velocity.
 The air is entered in a diffuser ring and paasing out at a
high pressure.
 The high pressure air then flows to passage of volute
casting and velocity is reduced due to increased cross
sectional area and then finally air comes out of a
compressor.

20. AXIAL FLOW COMPRESSOR

21.  In this compressor air flows parallel to the axis of
compressor.
 It consisting of several rows of fixed blades and rotor
attached with several rows of moving blades.
 The fixed and moving blades are placed on alternate rows.
 The fixed air receive high velocity air and they decrease the
velocity and increase the pressure of air and direct to next
row of moving blades.
 The basic working principle is same as the centrifugal
compressor.

22. ROOTS BLOWER

23.  For high pressure ratio, three or four lobes may be used.
 It is consist of fixed casting which contains two shafts fitted with
two lobe rotors.
 One is driven by motor or prime mover and other one through
gears from first.
 The air is drawn through the inlet pipe due to rotation of the
rotors.
 Due to rotation of lobes trapped air is carried to discharge side.
 Continued rotation of rotors, opens the trapped space to the
discharge port.
 The air is pushed to the receiver due to the continued rotation of
rotors.

24. VANE TYPE COMPRESSOR

25.  It is consist of rotor drum mounted eccentrically in the cylinder
casting.
 The rotor is provided with vanes and they remain in contact with
the wall of casing due to centrifugal force .
 The vane can slide in and out in the slots and volume between
two vanes keeps changing due to motion of the rotor.
 With the rotation of rotor, trapped air between the vanes and
casing gets compressed due to reduction of space towards
delivery side.
 Since the receiver pressure is higher than the compressed air
between the vanes, the back flow of air from the receiver will
take place.

26.  This is cause increase in the pressure.
 Due to rotation of vanes air is delivered to receiver.
 This type of compressor can produce a pressure ratio up to 6
per stage.