The document provides an overview of air compressors, including types, selection criteria, and components of compressed air systems. It discusses common compressor types (reciprocating, screw, and blowers), their merits and demerits, and factors affecting compressor selection such as location, pressure drop, and air quality. Additionally, it includes a calculation guide for determining compressed air requirements and ensuring optimal system performance.

1. Air Compressors
Overview and basic selection guide
Presented by - Anil Nair

2. Contents
oCompressed air systems - overview
oCommon compressor types
oCompressor types - Relative merits
oCompressed air system ancillary devices
oFactors affecting compressor selection
oHow to calculate minimum compressed air requirements
oFactors influencing optimal system performance
o Appendix 1 - Compressed air requirement calculation table
oAppendix 2 - Compressed air pipe sizing table

3. Compressed air system overview
oAir compressor is a mechanical device, usually powered by an electric motor,
that compresses the air prior treatment and distribution to end user
oCompressed air is used for driving a wide variety of devices in a factory or
warehouse including: process equipment, pneumatic conveying systems,
pneumatic tools, hoists, conveyors, actuators, sprayers, pumps, vacuum
filters etc.
o A compressed air system consists of
• Supply side – Included compressors and air treatment
• Demand side – Included distribution, storage systems and end-use equipment
oA properly designed and maintained compressed air system addresses both
the supply and the demand sides of the system
oThere are many types of compressors, hence a proper selection should be
followed to ensure the compressed air system works in balance

4. Common Air compressor types
Reciprocating compressors Rotary screw compressors Air blowers
General view Sectional view General view Sectional view General view Sectional view
Reciprocating piston within a cylinder
compresses the entrapped air and is
released to distribution system
Entrapped air is compressed between
the rotary screws and chamber and
released to distribution system
Entrapped air inside the void surrounding
the lobes is carried from the intake side to
the exhaust by high speed rotation of the
rotors

5. Air Compressor types - Relative merits
Type Merits Demerits
Reciprocating
o High efficiency on full, part and no load
o Easy to maintain
o Suitable for High pressure applications 10 Bar to 700 bar
o Suitable for high free air delivery i.e. upto 12000 m3/hr
o High noise levels
o Large size
o High oil carry over to the system piping (not for instrument air
application)
o High level of vibration
o High maintenance cost
o High electrical power consumption
Screw
o High efficiency only on full load
o High energy efficiency
o Low noise level
o Zero vibration level
o Low maintenance requirement
o Compact size
o Low oil carry over and suitable for instrument air
applications
o Suitable for medium pressure applications upto 8 Bar and
free air delivery upto 2400 m3/hr.
o Poor efficiency on part load
o Medium level efficiency on no load
o Expensive Compressor element
Blower
o Suitable for low pressure and high volume air application
o Operating range 0.15 to 1500 m3/hr.
o Pressure maximum upto 3.6 bar
o Constant flow rate at varying discharge pressure condition
o Low cost installation
o High noise levels
o High electrical energy consumption
o High maintenance costs

6. Compressed air system ancillary devices
o Intake air filters
• For supplying clean air to compressor element
o Compressor
• Integrated inbuilt Inter-stage and after-coolers
o For optimum efficiency of air compressor
• Air compressor element
• Integrated air-dryers
o Moisture drain traps
• To capture condensed water from the system and drain
o Filters, regulators and lubricators units
• Filter unit - for filtering water, oil mist etc.
• Regulator unit - to regulate the outlet air pressure
• Lubricator unit - to add lubricant to the distribution system
o External air drier unit
• For removal of all moisture from compressed air
o External air receiver tank
• High volume air reservoir to improve air compressor load cycle
o Pressure gauge
• To indicate the outlet system pressure
o External piping system for compressed air distribution
• Correct pipe sizing ensure consistent air delivery to end user - refer Appendix 2 Table 3 Compressed air system pipe sizes

7. Factors affecting Air compressor selection
o Location of installation
• Distance of piping will influence pressure drop in distribution system
• Intake temperature will influence overall efficiency
o Pressure drop inside pipe system
o Volume of air receiver
• Design of receiver affects loading cycle of compressor
o Air volume requirement in CFM (Cubic feet per minute) or lpm (Liters per minute)
o Air pressure requirement in bar or in kg/cm2
o Type of application
• High or Low pressure
o Required quality of air
• Dry, dust free, instrument, lubricated air etc.
o Type of air operated equipment

8. How to calculate minimum compressed air requirements and
select air compressor
 Refer Appendix 1 - Table 1 and 2 then follow steps 1 to 5 below
1. List equipment requiring compressed air (ref Table 1)
2. Confirm air requirements (ref table 1)
a) Volume
b) Pressure
3. Calculate total air requirement (ref table 1)
4. State system variables (ref table 2)
a) Diversity factor (typically 20%)
b) Pressure drop allowance (typically 10%)
c) Calculate
I. Maximum air requirement
II. Maximum calculated air demand
III. Maximum calculated pressure demand
5. Select the appropriate compressor and receiver from any manufacturer data sheet based
on
a) Volume - maximum calculated air demand
b) Pressure - maximum calculated pressure demand based on compressed air requirement calculation table 2

9. Factors influencing optimal system performance
o Intake air quality
• Dust content of air
o Intake air temperature
• Low ambient temperature improves system efficiency
o Location of Installation
• High altitude (low atmospheric pressure intake)
• Low temp air intake
o Pressure drop across the air intake filter
• Must be regularly maintained
o Pressure setting of compressor
• System pressure setting affects loading cycle
o Inter coolers and After coolers
• Must be maintained to remove scales (Water cooled units)
o External ancillary Equipment sizing
• Air drier – for capacity and pressure dew point
• Air receiver – for correct volume
o Air leakages from distribution system
• Has major influence on operating cost
o Accumulated water inside system
• Affects performance
• Causes damage to equipment

10. Appendix 1 - Compressed air requirement calculation table
o Site specific compressed air requirement summary-Table 1
Ref # Equipment name
Quantity
(Nos)
Air requirement per device
(CFM)
Total air
requirement
(CFM)
Working air
pressure in
(bar)
Remarks
1 Equipment 1 2 113 226 5.5 Instrument air
2 Equipment 2 1 28 28 6 Instrument air
3 Equipment 3 2 1 2 3 Lubricated air
4 Equipment 4 5 1.2 6 5.6 Filtered dry air
6 Total air requirement 262
Ref # Calculation
Total Air
Requirement
(CFM)
Maximum
Pressure (bar)
A
Total air requirement from equipment and compressed air requirement
summary from Table 1
262 6
B
Air requirement, assuming extra 20 % air requirement for friction loss,
leakage etc (CFM)
314
C Industry specific instantaneous operating/diversity factor (%) 20%
D Maximum calculated air demand (CFM) 63
E Distribution system pressure drop allowance (%) 15%
F Maximum calculated pressure demand (bar) 6.9
o Compressed air requirement calculation-Table 2

11. Appendix 2 - Compressed air system pipe sizes
o Pipe sizing-Table 3
Air Compressor
delivery CFM
Equivalent Pipe Length (Feet)
25 50 75 100 150 200 250 300
CFM Pipe Diameter (Inches)
1 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
2 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
3 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
10 0.5 0.5 0.5 0.75 0.75 0.75 0.75 0.75
15 0.5 0.75 0.75 0.75 0.75 0.75 0.75 0.75
20 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75
25 0.75 0.75 0.75 0.75 0.75 1 1 1
30 0.75 0.75 0.75 0.75 1 1 1 1
35 0.75 0.75 1 1 1 1 1 1
40 0.75 1 1 1 1 1 1 1
50 1 1 1 1 1 1 1 1
60 1 1 1 1 1.25 1.25 1.25 1.25
70 1 1 1 1 1.25 1.25 1.25 1.25
80 1.25 1.25 1.25 1.25 1.5 1.5 1.5 1.5
100 1.25 1.25 1.25 1.25 1.5 1.5 1.5 1.5
125 1.25 1.25 1.25 1.25 1.5 1.5 1.5 1.5
150 1.25 1.25 1.25 1.25 1.5 1.5 1.5 1.5
175 1.5 1.5 1.5 1.5 2 2 2 2
200 1.5 1.5 1.5 1.5 2 2 2 2
225 1.5 1.5 1.5 1.5 2 2 2 2

12. THANK YOU