Atlas Copco-Basic Product Training

Basic Product Training
Chapter 1. Air
What is Air? Air is colourless, odourless and tasteless. It is a mechanical mixture of individual gases mainly
Nitrogen (N2 , 78%), Oxygen (O2 , 20.9%), Argon (0.9%) and other gases.
What is water? Water is a pure substance due to its constant chemical composition whether it exists as a solid, a
liquid, a vapour or any mixture of the three.
Air is not a pure substance, its composition varies when it is in a mixture of the gaseous and liquid phases. However,
gaseous air exhibits many of the characteristics of a pure substance.
The composition of the air remains relatively constant from sea level up to an altitude of at least 20 km.
The air in the atmosphere contains gases, water vapour and solid particles like dust, sand, soot and crystals of salts.
Because of air is a mechanical mixture and not a chemical substance the components can be separated. At -196oC air
components may be separated by fractional distillation. Of the air constituents which make up air, only oxygen and
nitrogen are necessary for animal life.
1.1. Oxygen (O2):

O2
Carbohydrates + Proteines + Fat Heat + Energy
∆
An average person consumes:
740liters O 2 ⇒ 1kg O 2 ⇒ 1 kg of food
24h 24h 24h
1.2. Nitrogen (N2):

- no metabolic function
- Serves as inert gas and maintains inflation of certain gas filled body cavities such as
pulmonary alveoli, the middle ear and the sinus cavities.
1.3. Reference tables

boiling point 78.8 K
critical pressure (absolute) 37.66 bar
critical temperature 132.52 K
density 1.225 kg/m³
dynamic viscosity 17.89. 10-6 Pa.s
freezing point 57- 61 K
gas constant 267.1 Jl(kg. K)
kinematic viscosity 14.61 10-6 m²/s
mean collision diameter 0.365.10-9 m
molar mass 28.964 (dimensionless)
specific heat-capacity at constant pressure 1.004 kJ/(kg. K)
specific heat-capacity ratio 1.40 (dimensionless)
speed of sound 340.29 m/s
thermal conductivity 0.025 W/(m. K)
T00able 1: Some physical constants of dry air at sea level (+15°C and 1.013 bar)
page 2/42
Constituent0 Per cent by volume Per cent by mass

Nitrogen (N2) 78.084 75.520
Oxygen (O2) 20.9476 23.142
Argon (Ar) 0.934 1.288
Carbon dioxide (C02) 0.031 4 0.047 7
Neon (Ne) 0.001 818 0.001 267
Helium (He) 0.000 524 0.000 0724
Krypton (Kr) 0.000 114 0.000 330
Xenon (Xe) 0.000 008 7 0.000 039
Hydrogen (H2) 0.000 05 0.000 003
Methane (CH4) 0.000 2 0.000 1
nitrous oxide (N2O) 0.000 05 0.000 08
Ozone (O3) summer:
0 to 0.000 007 0 to 0.000 01
winter:
0 to 0.000 002 0 to 0.000 003
Sulphur dioxide (SO2) 0 to 0.000 1 0 to 0.000 2
Nitrogen dioxide (NO2) 0 to 0.000 002 0 to 0.000 003
Ammonia (NH3) 0 to trace 0 to trace
Carbon monoxide (CO) 0 to trace 0 to trace
iodine (I2) 0 to 0.000 001 0 to 0.000 009
Table 2: The composition of clean dry air near sea level (the composition remains relatively constant up to
an altitude of about 25 km)
Chapter 2. Free air delivery (F.A.D.)
2.1. Concept:
Free air delivery is the volume flow rate of gas compressed and delivered at the standard discharge point, referred to
the atmospheric conditions of the site, not affected by the compressor. F.A.D. can be expressed in l/s, m3/min or cfm.
Atlas Copco uses F.A.D. to rate its displacement compressors. Flow measured at the discharge flange of packaged
compressor as stipulated by ISO 1217 annex C (downstream of the aftercooler, check valve and water separators)
referred back to ambient conditions on site.
Reference ambient conditions according to ISO 1217:
Ambient temp. = 20ºC
Bar pressure = 1 bar
Relative Humidity = 0%
Other representations of capacity may often be used by competitors and are explained as follows.
2.2. Standard/ Normal Volume Flow Rate

Volume flow rate of gas compressed and delivered at the standard discharge point, but with reference to Standard/
Normal conditions for temperature, pressure and inlet gas composition (humidity).
Standard Conditions Normal Conditions
Temp. = 15.6ºC Temp. = 0ºC
Bar pressure = 1.013 bar Bar pressure = 1.013 bar
Relative humidity = 0% Relative humidity = 0%
2.3. Inlet Volume Flow Rate (Im3/min or Icfm)

Volume flow rate of gas at the standard inlet point, i.e. inlet flange first stage for centrifugals.
Temp. = 35ºC
Pressure (at flange) = 0.975 bar (e)
Relative humidity = 60%
page 3/42
2.4. Actual Volume Flow Rate (Acfm)

Volume flow rate of gas compressed and delivered at the standard discharging point, with reference to conditions
prevailing at the standard inlet point. (Inlet of the element)
page 4/42
2.5. Correction calculation – site conditions other than reference
2.5.1. Temperature Corrections

As already stated, Atlas Copco uses F.A.D. to rate the volumetric capacity of its compressors at reference conditions
as per ISO 1217. {Temp. = 20ºC, Barometric pressure = 1 bar, Relative Humidity (Rh) = 0%}
Therefore a correction must be made to calculate the F.A.D. if the site conditions differs from the reference
conditions, using the following formulae:
FAD ×  1  × (273 + Ambient Temp.)


 Ambient barometric pressure 
Site condition FAD =
273 + Reference temp.
P1V1 P2 V2 V1 ×  1  × T1
P
Using formulae:
= as a reference and V2 =
 P2 
T1 T2 T2
Where:
- P= pressure in bar
- V= volume in l/s
- T= Temperature in Kelvin (°C+273)
Example of a different Temperature:

Ambient Temp. (T2)= 30ºC
Barometric press. (P2)= 1.013 bar(e)
F.A.D. required (V2)= 50 l/s
Site conditions FAD:

50 × 1(
1.013
)
× (273 + 30 )
= 51.04 l/s
273 + 20
Taking into account the temperature at site, 51.04 l/s is the corresponding capacity flow of the compressor that
would be needed to satisfy the requirement of 50 l/s with an ambient temperature of 30°C.
It is interesting to note that when keeping the intake pressure constant, (1.013 bar in this example) the needed
compressor FAD will increase with a higher intake temperature.
This is easily explained with the air density; If the air temperature is higher, the air is less dense and to get the same
weight of air more air has to be delivered.
Something similar can be said about a variable intake pressure with a constant intake temperature. If the pressure is
lower (due to high altitude for example) the air is less dense and again to get the same weight of air more air has to
be delivered. (See the example further on).
2.5.2. Relative humidity

The next step is the relative humidity. As you have noticed in the previous example we talked about dry air, but in
practically all cases the air sucked into the compressor has a relative humidity, therefore a basic formula out of the
thermodynamic formula can be used:
FAD (dry air)

FAD (wet air) =
1 - 
(Rh × Ps1 ) 
 P1 
Where:
- Rh = relative humidity of the air intake (ex. 60% Relative humidity = 0.6)
- PS1= Water vapour, this is the saturation pressure in bar at air intake temperature (See table 3, column Ps mbar).
- P1= absolute intake air pressure, in bar.
page 5/42
Temp pS ρW Temp pS ρW Temp pS ρW Temp pS ρW

°C mbar g/m³ °C mbar g/m³ °C mbar g/m³ °C mbar g/m³
-40 0.1283 0.1192 -10 2.591 2.139 20 23.37 17.30 50 123.4 83.06
-39 0.1436 0.1329 -9 2.837 2.328 21 24.86 18.34 51 129.7 87.01
-38 0.1606 0.1480 -8 3.097 2.532 22 26.43 19.43 52 136.2 91.12
-37 0.1794 0.1649 -7 3.379 2.752 23 28.09 20.58 53 143.0 95.39
-36 0.2002 0.1829 -6 3.685 2.990 24 29.83 21.78 54 150.1 99.83
-35 0.2233 0.2032 -5 4.015 3.246 25 31.67 23.05 55 157.5 104.4

-34 0.2488 0.2254 -4 4.372 3.521 26 33.61 24.38 56 165.2 109.2
-33 0.2769 0.2498 -3 4.757 3.817 27 35.65 25.78 57 173.2 114.2
-32 0.3079 0.2767 -2 5.173 4.136 28 37.80 27.24 58 181.5 119.4
-31 0.3421 0.3061 -1 5.623 4.479 29 40.06 28.78 59 190.2 124.7
-30 0.3798 0.3385 0 6.108 4.847 30 42.43 30.38 60 199.2 130.2

-29 0.4213 0.3739 1 6.566 5.192 31 44.93 32.07 61 208.6 135.9
-28 0.4669 0.4127 2 7.055 5.556 32 47.55 33.83 62 218.4 141.9
-27 0.5170 0.4551 3 7.575 5.947 33 50.31 35.68 63 228.5 148.1
-26 0.5720 0.5015 4 8.129 6.360 34 53.20 37.61 64 239.1 154.5
-25 0.6323 0.5521 5 8.719 6.197 35 56.24 39.63 65 250.1 161.2

-24 0.6985 0.6075 6 9.347 7.260 36 59.42 41.75 66 261.5 168.1
-23 0.7709 0.6678 7 10.01 7.750 37 62.76 43.96 67 273.3 175.2
-22 0.8502 0.7336 8 10.72 8.270 38 66.26 46.26 68 285.6 182.6
-21 0.9370 0.8053 9 11.47 8.819 39 69.93 48.67 69 298.4 190.2
-20 1.032 0.8835 10 12.27 9.399 40 73.78 51.19 70 311.6 198.1

-19 1.135 0.9678 11 13.12 10.01 41 77.80 53.82 71 325.3 206.3
-18 1.248 1.060 12 14.02 10.66 42 82.02 56.56 72 339.6 214.7
-17 1.371 1.160 13 14.97 11.35 43 86.45 59.41 73 354.3 223.5
-16 1.506 1.269 14 15.98 12.07 44 91.03 62.39 74 369.6 232.5
-15 1.652 1.387 15 17.04 12.83 45 95.86 65.50 75 385.5 241.8

-14 1.811 1.515 16 18.17 13.63 46 100.9 68.73 76 401.9 251.5
-13 1.984 1.650 17 19.37 14.48 47 106.2 72.10 77 418.9 261.4
-12 2.172 1.803 18 20.63 15.37 48 111.1 75.61 78 436.5 271.7
-11 2.376 1.964 19 21.96 16.31 49 117.4 79.26 79 454.7 282.3
Table 3 : Saturation Pressure ps and Density ρw of water vapour at

saturation. Values below 0°C refer to saturation above ice.
Example:
Let us now continue with our previous example: for 30°C and 1.013 bar intake conditions of dry air we needed a
capacity of 51.04 l/s. If we correct this now for a relative humidity of 60% we come to the following:
51.04
FAD (wet air) = = 52.5 l/s
 0.6 × 0.04243 
1-  
 1.013 
Conclusion:
In this example the customer specified 50 l/s (corresponding to a GA18 at 7.5 bar). We have in fact to offer a
compressor able to deliver 52.5l/s this because of the fact that the FAD of 50 l/s are for standard reference conditions
(20°C, 1.013 bar and dry air (Rh=0%). In this case, for the same working pressure we will have to propose to the
customer a GA 22 with a FAD of 60l/s at 7.5 bar.
page 6/42
2.5.3. Correction for Altitude operations

The air inlet conditions usually differ from the AML standard inlet conditions.
Altitude Pressure Denisity
AML Standard inlet conditions are:
- Dry air (m) (bar) (kg/m³)
- 20°C inlet air temperature -1000 1,138 1,345
- 1 bar absolute air intake pressure -800 1,109 1,317
- 20°C inlet coolant temperature. -600 1,080 1,288
Example -400 1,062 1,272
The customer would like to install a GA type compressor. -200 1,038 1,249
Required air flow rate: 0.271 kg/s at 7 bar effective corresponding to 222 l/s at 0 1,013 1,225
AML conditions.
100 1,001 1,213
Altitude of operation: 2000 m
Corresponding air inlet pressure: 0.795 bar absolute (see table 4) 200 0,989 1,202
300 0,978 1,190
2.5.3.1. Capacity and altitude operation 400 0,966 1,179
500 0,955 1,167
2.5.3.1.1. Influence of Barometric pressure 600 0,943 1,156
800 0,921 1,134
Solution convert the mass of the required air flow rate to Free Air Delivery by the
1000 0,899 1,112
formula pV = mRT 1200 0,877 1,090
1400 0,856 1,069
mRT 1600 0,835 1,048
V= 1800 0,815 1,027
p 2000 0,795 1,007
Where: 2200 0,775 0,986
P= Absolute pressure (Pa) 2400 0,756 0,966
V= volume (m³) 2600 0,737 0,947
m= mass of the gas (kg) 2800 0,719 0,928
R= gas constant: 287.1 J/(kg.K) for dry air 3000 0,701 0,909
T= absolute temperature (K)
3200 0,683 0,891
0.271 × 287.1 × (273 + 20 )
3400 0,666 0,872
V= =0.287m³/s = 286.75 l/s 3600 0,649 0,854
0.795 × 105 3800 0,633 0,837
We can see after this calculation that the GA 75 will not deliver as much air as the 4000 0,616 0,819
customer requires due to the specific site conditions. We then will have to find
5000 0,540 0,736
another solution for him.
6000 0,472 0,660
7000 0,411 0,590
8000 0,356 0,525
2.5.3.1.2. Influence of pressure ratio Table 4: Air pressure (Absolute)

and Density at different altitudes
A working pressure of 7 bar effective at 0.795 bar absolute inlet pressure (2000 m) according to NASA
correspond to a pressure ratio of:
7 + 0.795
Pressure Ratio = = 9.81
0.795
A pressure Ratio of 9.81 corresponds to 8.81 bar effective working pressure at 1 bar absolute inlet pressure (AML
conditions).
By making a linear regression on the AML data it is easy to find the FAD to a specific atmospheric pressure.
Example with the new pressure ratio for a GA75 / 50 Hz = 220.3 l/s (the AML data is 222 l/s)
Although the influence of pressure ratio in altitude is minimal for screw type compressors, it can be more important
for a piston compressor.
page 7/42
2.5.3.2. Power consumption and Altitude operations
Reduction factor for shaft input at altitude operation

The shaft input is proportional to the pressure ratio
Factor
1
and the inlet pressure.
For our GA 75P 50Hz 0,95
The shaft input at 9.81 bar effective = 80.3 kW at 1
0,9
bar absolute inlet pressure (extrapolated by linear
regression from the AML data = 84 kW at 7 bar). 0,85
0,8
This value has to be multiplied by a correction
factor 0.892 because of the low inlet pressure (See 0,75
−5
graph or formula: y = −6,667.10 x + 1 ). 0,7
0 1000 2000 3000 4000 5000
Note: The reduction factor is an approximation and
should only be used as a preliminary calculation Meters
The corrected shaft input is then: 0.892 x 80.3 = 71.6 kW. Graph 1: Reduction factor for
shaft input at altitude operation
The compressor will consume less power at a higher altitude…
2.6. Noise level measurement

Sound is a form of energy that is propagated by longitudinal waves throughout an elastic medium (in most cases
through the air).
From a soft whisper to the roar of a large rocket engine, the level of sound varies so widely that, when measured in
the conventional unit of watts, handling the wide range of values is difficult. Therefore, a more convenient unit for
measuring or comparing sound powers has been thought.
In acoustics, the term “level” is used whenever a comparison, or ratio, of a quantity to a reference quantity is made.
Taking the logarithm of this ratio greatly reduces the numerical notation so that the range becomes more
manageable.
Sound power Sound power
(watts) level (dB)
1000,000,000 200
10,000,000 190 Rocket
1,000,000 180
100,000 170 Jet
10,000 160
1,000 150
100 140
10 130
1 120 Disco bar
0.1 110
0.01 100 Unsilenced compressor
0.001 90
0.000,1 80
0.000,01 70 Silenced compressor
0.000,001 60 Normal conversation
0.000,000,1 50
0.000,000,01 40 Soft whisper
0.000,000.001 30
Table 5: Sound power and power level
According to ISO standards and Cagi-Pneurop, standards and principals do exist and a manufacturer may choose to
measure the noise level of their compressors as per any of the methods as long as they declare the relevant code that
was applied.
The old measuring code was according to the ISO 2151 standard which only takes into account the sound pressure
level noise of the compressor measured at certain points around the compressor at a prescribed distance and height.
page 8/42
This has led to subjective representations of noise level by manufacturers as the tests could be arranged so as to
obtain the lowest possible dB(A) level.
Certain manufacturers are still using this ISO standard as form of measurement and are using adapted code names as
declaration of measurement e.g. Hitachi Code and J.I.S.
2.6.1. Definitions
SOUND PRESSURE is a fluctuating pressure superimposed on the static pressure by the presence of sound. It is
expressed in Pascal.
SOUND PRESSURE LEVEL: Ten times the logarithm to the base 10 of the ratio of the square of the sound pressure
to the square of the reference sound pressure. Sound pressure levels are expressed in decibels.
The reference sound pressure is 20mPa.
SOUND INTENSITY is the time-average value of instantaneous sound intensity in a temporally stationary sound
field.
SOUND POWER is the rate per unit time at which sound energy is radiated by a source.
SOUND POWER LEVEL: ten times the logarithm to the base 10 of the ratio of the sound power radiated by the
source under test to the reference sound power.
FREE FIELD: A sound field in a homogeneous, isotropic medium free of boundaries.
2.6.2. Hitachi Code

This is a noise pressure level obtained from a measurement taken at one point away from the compressor.
(the operator position??) at a distance of 1.5m and a height of 1.0m above the ground. The measurement is not taken
in a free field but in a sound proof room, therefore no reverberating sound is included.
2.6.3. Cagi-Pneurop
The Cagi-Pneurop measuring codes, according to the ISO 2151, follows a similar principle in that only the sound
pressure level is measured and the sound power level is not taken into account.
The measurements taken as per this code are 1.0m away from the compressor and at a height of 1.5m above the
ground. The number of measuring points (microphones) varies from 5-9 equally spaced in a measuring field around
the reference point or noise source - the compressor in this case.
From this type of measurement the sound pressure levels are represented as measured.
2.6.4. PN8NTC2.2
In an effort to create one standard or the same standard the ISO 3744 combined with the ISO 9414/2 standards have
been adopted and implemented taking the sound power level and sound pressure level into account to establish the
most accurate noise level for representation – the PN8NTC2.2 code.
page 9/42
Chapter 3. Compressor Range

Atlas Copco develops manufactures and markets industrial, oil-free and portable compressors, generators, specially
built gas and process compressors, expansion turbines and cryogenic pumps. Supplementary products are air dryers,
after coolers, energy recovery systems, control systems and filters.
3.1. Piston Principles
3.1.1. Basic build-up
Figure 1: Typical Single Stage LE/LF compressor
Figure 2: Inlet Valve
page 10/42
3.1.2. Main compressor components
Figure 3: Air flow and regulating system
Air pressure switch (MDR3) opens and closes its contact at pre-set pressures. During loaded operations, the contacts
are closed: the motor is running.
When the pressure in the air receiver reaches the pre-set maximum pressure, the contacts as well as pressure relieve
valve are opened. The motor stops, the air at the delivery side of the compressor is vented to atmosphere and check
valve (CV closes to prevent venting of the receiver.
When the pressure in the air receiver decreases to the pre-set minimum pressure, the contact of the pressure switch
closes and pressure release valve closes. The motor restarts and compressed air is supplied to the receiver again.
page 11/42
3.1.3. Flows and circuits

Basically the piston compressor utilise the same principles as the bicycle pump.
To illustrate the compression principles it is best to use a theoretical pressure volume diagram for a displacement
compressor.
1-2 Compression
2-3 Discharge
3-4 Return
4-1 Intake (suction)
At position 1: The piston starts to compress the gas along line 1-2 in the cylinder. At the same time, the suction
valves close and shut-off the cylinder from the suction line.
At position 2: The pressure in the cylinder is slightly higher than that existing in the discharge line and the
discharge valves open, allowing the piston to push the compressed air out of the cylinder into the
discharge system along the line 2-3.
At position 3: The piston complete its discharge stroke. However, there is clearance volume which the air is
trapped between the end of the piston and the end of the cylinder. As its return stroke, the pressure
in the cylinder drops and the discharge valve closes. Air expands along 3-4 until pressure is slightly
lower than the suction pressure.
At position 4: The suction valves open and the cylinder starts to drain air from the suction line. The intake stroke
occurs from position 4-1.
The shaded area, is the required work to generate that amount of air.
It is interesting to note that in real life the volume flow rate of a real compressor is, however, smaller than the
theoretical swept volume because of:
• pressure drop on the suction side
• heating up of the intake air
• expansion of the gas trapped in the clearance volume
• internal and external gas leakage
page 12/42
3.2. Scroll principles

Each compressor element consists of a fixed scroll shaped having a scroll shaped rotor. Air enters the compressor
element through inlet opening (1). Once the air is drawn in, the orbit scroll (4) seals the inlet opening and forces the
air into a continuously decreasing space. As scroll (4) keeps orbiting, this process of compressor is constantly
repeated, resulting in discharging continuos oil-free compressed air through outlet opening (3).
1. Air Inlet
2. Fixed Scroll
3. Compressed air
Outlet
4. Orbiting Scroll
Figure 4: Scroll Compressor element
Figure 5 : Working principle of the Scroll element
page 13/42
3.2.2. Main compressor component

Scroll compressor element
Opposing helical elements orbit in relation to
each other, progressively compressing
atmospheric air up to 10 bar pressure. There is
no metal to metal contact whatsoever - hence no
need for lubrication. A minimum of moving
components ensures inherent reliability,
minimum maintenance and guarantees
continuous operation.
Air intake filter

The air inlet filter is a dry paper filter cartridge
ensuring optimal filtration. Replacement is easy
and accessibility optimal.
Drive system
All SF models are V-belt driven, using belts
with XPZ profile.
Belt tensioning is easy as adjusting bolts are
easily accessible via the front door.
Electric motor
The foot mounted motors SF units are totally enclosed fan cooled drive motors of high specification with high
efficiency, IP 55 protection and class F insulation.
Cooling
SF series are aircooled. A radial fan on the compressor element forces the cooling air flow over the cooling fins of
the scroll element. Cooling air is evacuated via the rear panel or alternatively via the top panel. Top and rear panel
are therefore fully interchangeable and cooling air ducts can be mounted easily.
Instrument panel and controlling/regulating system

All SF units have direct on line starters. Load / No Load regulation is used, ensuring the most economical operation.
An easy to read control panel enables an easy operation and perfect supervision of the unit.
Aftercooler
The finned copper tube aftercooler is placed in the cooling air flow, ensuring a maximum air outlet temperature of
ambient plus 30 °C.
Air receiver
SF models are equipped with a 16 l air receiver or with two 16 l receiver in series. The receivers have an anti-
corrosion treatment both on in and outside.
Integrated refrigeration dryer

SF full feature variants have an integrated refrigeration dryer. The integration of the FD dryer results in a compact
compressed air installation, avoiding a lot of pipework and connections.
The integrated refrigeration dryer has the following characteristics:

- A compact aluminium air to air and air to refrigerant heat exchanger.
- Hermetically sealed rotary freon compressor
- integrated WSD25 water separator with automatic and manual drain
- analogue pressure dewpoint indicator.
page 14/42
3.2.3. Flow and circuits

Referring to the figure 5 the air compression is achieved by the interaction of a fixed and orbiting scroll. Air at inlet
pressure enters the compression chambers at the exterior side of the scroll element. Once air is drawn in, the orbiting
scroll seals off the inlet port. As the scroll continues to orbit , the air is progressively compressed into an increasing
smaller “pocket”. A continues flow of compressed air leaves the scroll element through a discharge port in centre of
the fixed scroll. This compression process is endless repeated, generating pulsation free air delivery.
3.3. Screw principle

These are positive displacement compressors with a built in pressure ratio. Figure 6
shows the working principles. As there no inlet and outlet valves and no unbalanced
mechanical forces, the screw compressor operates at high shaft speed. Consequently it
combines high flow rates with small exterior.
Dry type screw compressors use external timing gears to synchronise the counter
rotating male and female rotors. As the rotors touch neither each other nor the casing,
lubrication is not required within the compressor space. The delivered air is oil free.
However, if the compressor space is oil-flooded by injection of oil then shaft speeds
may be lowered. The injected oil has three functions:
to seal the internal clearances
to cool the air during compression
to lubricate the rotors
The internal lubrication makes it possible to dispense with the timing gears. The
injected oil is reclaimed and recirculated after compression. As the maximum oil
temperature can be kept low it is possible to reclaim practically all the oil. The oil
reclamation is in two stages:
first with a mechanical separator
then with a terminal pad type oil filter mounted inside the air receiver
The injection is usually accomplished by using the discharge pressure. Sometimes a

separate scavenging pump is used. A minimum pressure valve is used to ensure that oil
is injected even if the discharge pressure should drop.
3.3.2. Main compressor component

To simplify the illustration of all type of compressor, GA 55-75 Full Feature
compressor is chosen to illustrate the main component in the rotary screw compressor.
3.3.2.1. Air inlet filter

The air inlet filter is of heavy duty type. This means that the particle Figure 6: Working principle of a screw
separation takes place in two stages, first by cyclonic action before the inlet air compressor
is sucked through the filter. The efficiency of the filter is 99.9% for particle
sizes greater or equal to 3 µm.
This two-stage filter is suitable for dusty environments. Alternatively service intervals will be extended when it is in
a normal industrial environment.
3.3.2.2. Air intake valve

The air intake valve is of the monoblock type, integrating all pneumatic regulation functions of the compressor. The
piston valve used for the following advantage:
simple design with only one moving part ( the piston), needs no regular adjustments.
3.3.2.3. Compressor element

The compressor element used in the new GA 55-75 is the proven size 1.5, which has rotors with large diameters and
therefore rotate at a low speed, for a long life time of operation.
page 15/42
The compressor element is optimised to bring performance especially on higher pressures.
3.3.2.4. Non return valve

This unit serves as one way valve for the air flows to the air/oil separator vessel.
3.3.2.5. Air/Oil separator vessel

The air/oil separation system removes the oil from the compressed air three stages. First by cyclonic action, then by
gravitation and change in direction and finally in the third stage the air passes through the final separator filter. The
air leaving the unit has an oil content of less 2mg/m3 (2ppm).
3.3.2.6. Minimum pressure vessel

The minimum pressure vessel is used to control air flows to aftercooler where a minimum pressure of the valve has
to be overcome.
3.3.2.7. Aftercooler- oil & air

Aircooled versions oil & air after cooler is compact block cooler of aluminium for optimal heat transfer, low
pressure drop and low weight. The aftercooler reduces the temperature of the outlet air to approximately 10°C
above ambient temperature.
3.3.2.8. Air to air heat exchanger

This is where the inlet air temperature exchange heat with outlet compressed air.
3.3.2.9. Air & Refrigerant heat exchanger

To cool compressed air to minimum temperature so that most of the water vapour is condensate.
page 16/42
3.3.3. Flow and Circuit
Figure 7: GA 30-75 Full feature flow diagram
3.3.3.1. Oil flow

Oil sump
The oil sump is the vessel to collect all condensate oil to be re-circulated to the system.
Oil cooler
To cool oil before going into the system.
Thermostatic by-pass valve

It is use as a thermostatic control valve to control oil into the compressor element.
Oil filter
To filter the oil of the compressor element.
Oil stop valve

To control oil injected to the compressor element.
3.3.3.2. Refrigerant flow

The main design features for the dryers are:
− environmental friendly refrigerant 404a
− compact aluminium air to air and air to refrigerant heat exchangers
− hermetically sealed freon compressor.
− integrated WSD 250 water separator with automatic and manual drain
− digital pressure dew point indicator with a read out on the “Elektronikon” displays
The integration of the refrigerant dryers makes installation more compacts and for less complicated. These dryer
modules are built in such a way that they can be installed afterwards as a “ dryer -kit”.
page 17/42
3.3.3.3. Drive System

The GA55/ 7.5 bar / 50 Hz is a direct driven variant. All other units have a gearbox transmission. The coupling
used is of a special design to reduce the torque peaks at start. The coupling housing is connected to the element
directly to the motor permanent alignment to optimise the reliability of the drive system.
3.3.3.4. Electric Motor

Reference Standards: IEC 529
Standards IP codes for Motor Protection
First Numeral DEGREE OF PROTECTION (First Number in Code)
Characteristic
Brief Description Definition
0 Not protected -
1 Protected against solid foreign objects The object probe, sphere of 50mm diameter, shall not fully
of 50mm diameter and greater. penetrate1
2 Protected against solid foreign objects The object probe, sphere of 12.5mm diameter, shall not fully
of 12.5mm diameter and greater penetrate.1
3 Protected against solid foreign objects The object probe, sphere of 2.5mm diameter, shall not
of 2.5mm diameter and greater. penetrate at all.1
4 Protected against solid foreign objects The object probe, sphere of 1mm diameter, shall not
of 1mm diameter and greater. penetrate at all.1
5 Dust-protected Ingress of dust is not totally prevented, but dust shall not
penetrate in a quantity to interfere with satisfactory operation
of the apparatus or to impair safety
6 Dust-tight No ingress of dust.
1
The full diameter of the object shall not pass through an opening of the enclosure
Second DEGREE OF PROTECTION (Second Number in Code)

Numeral
Characteristic
Brief Description Definition
0 Not protected
1 Protected against vertically falling Vertically falling drops shall have no harmful effects
water drops
2 . Protected against vertically falling Vertically falling drops have no harmful effects when the
water drops when enclosure is titled up enclosure is tilted at any angle up to 15° on either side of the
to 15°. vertical
3. Protected against spraying water. Water sprayed at an angle up to 60° degrees on either side of
the vertical shall have no harmful effects.
4 Protected against splashing water. Water splashed against the enclosure from any direction
shall have no harmful effects.
5 Protected against water jets. Water projected in jets against the enclosure from any
direction shall have no harmful effects
6 Protected against powerful water jets Water projected in powerful jets against the enclosure from
any direction shall have no harmful effects.
7 Protected against the effects of Ingress of water in quantities causing harmful effects shall
temporary immersion in water. not be possible when the enclosure is temporarily immersed
1 meter in water under standardised conditions of pressure
and time.
8 Protected against the effects of Ingress of water in quantities causing harmful effects shall
continuous immersion in water. not be possible when the enclosure is continuously immersed
in water under conditions which shall be agreed between
manufacturer and the user, but are more severe than for
number 7
Table 6 : Standard IP code IEC 579 Reference Standards: IEC 34-1, BS 4999, AS 1359.32.
page 18/42
3.3.3.5. Temperature Rise and Motor Life

The “Life” refers to the life of the windings before they require rewinding. The Temperature rise of the windings,
(and the insulation materials), of an electric motor is critical to the life expectancy of the motor, and is a function of
the design of the motor. The insulation materials age overtime and this ageing process is directly related to
temperature. Eventually the materials lose their insulating properties and break down causing a short circuit.
The increase in temperature of a motor is due to the losses that occur in the motor. These loses are mainly made up
of copper and iron losses. The temperature inside the motor will depend on how effectively this heat can be removed
by the cooling system of the motor. It should not be assumed that a motor that appears to be hot externally, is hot
internally.
If the cooling system is efficient the thermal gradient through the motor will be small and the difference between the
winding temperature and the external temperature low.
Some standards estimate the life of the insulation materials as 25, 000 hours if operated continuously at their rated
temperature that the life will be reduced by 50% for every 10 degrees of excess temperature.
Insulation Class A E B F F with H

B Rise
Temperature Rise 105 120 130 155 155 180
Maximum Temp of the
100 115 120 140 140 165
Winding
Ambient Temperature 40 40 40 40 40 40
Allowance for Hot Spots 5 5 10 15 15 15
Maximum Temp Rise of
60 75 80 100 80 125
Winding
Thermal Reserve 0 0 0 0 20 0
Table 7 : Insulation Class
3.3.3.6. Temperature Limits

The permitted temperature rises of the windings of an electric motor are subdivided into different insulation classes
and temperature limits.
The above table applies for motors in an ambient temperature up to 40°C and an altitude of less than 1000 meters
above sea level.
The difference between the 'Maximum Temperature of the Winding' and the 'Temperature Limit' is because there
will be hot spots in the winding which are not measured by the 'Resistance Method' which only measures the Mean
Temperature of the whole winding. An Allowance is made for this difference to ensure that no part of the winding is
operating at it's full thermal rating. It is not considered to be practical to try to locate and measure the hottest spot in
a winding.
The temperature rise of the winding is measured by the resistance method using the following formula:
(R 2 − R 1 )
DT =
(235 + T1 ) + (T1 − T2 )
Where:
DT= Temperature Rise in deg. K.
R1 = Cold resistance of the Winding @ T1
R2 = Hot resistance of the Winding @ T2
T1 = Ambient @ Start up deg. C.
T2 = Ambient @ Finish in deg. C.
235 = Reciprocal of the temperature Coefficient of the resistance of Copper at 0°C.
For a winding to comply with Class F insulation requirements all the materials must be to Class F specification or
better.
3.3.3.7. Advantages of Thermal Reserve

There are a number of advantages in buying motors with a thermal temperature reserve apart from an anticipated
long service life.
page 19/42
3.3.3.7.1. Service Factor.

This is really an American, (NEMA), term that is not covered in IEC standards. It means that the motor can be
overloaded without serious damage of overheating.
Typically NEMA specifications call for Service Factors of 1.1 or 1.15, meaning a 10% or 15% overload. Service
Factor is in fact using up the thermal reserve of the motor and allowing it to operate at its full Class temperature rise.
Although IEC does not acknowledge Service Factor in the same way it certainly allows motors to operate to their full
class rating and in fact most motors with a generous thermal reserve will easily match the NEMA requirement for 1.1
or 1.15.
Service Factor and duty rating, e.g. S1, S2, etc, should not be confused. Duty ratings are clearly covered in IEC
standards for different repetitive short term overloads which can be defined and simulated to ensure the motor still
meets the requirements for temperature rise.
3.3.3.7.2. Voltage of Frequency variations.

In some installations, especially with their own power generation, or a very weak grid, large fluctuations in voltage
and/or frequency are possible, which can cause increases in the temperature rise of the motor. Motors with a large
thermal reserve can operate in these conditions usually without exceeding their Class rating by using some or all of
their thermal reserve, depending on how large the fluctuation is.
3.4. Control/regulation system and instrument panel

The GA 5-75 series are equipped with the user-friendly “Elektronikon” system that features a clear alphanumeric
display.
The “ Elektronikon” system continuously and accurately monitors the status of the compressor and automatically
regulates the unit for economic and efficient operation. It can be programmed for each day of the week with a start
and stop time.
The full load/ no load is the most efficient regulating method from power consumption point. When compressed air
pressure reaches the maximum level, the airflow into the element is stopped.
The compressor gives no output, until the compressed air falls to the minimum pressure level.
The delayed second stop feature (DSS) of the “ Elektronikon” regulation cuts energy consumption significant by
stopping the motor as fast as possible when the compressor switches to no load. This reduces no load power
consumption drastically.
The high range “ Elektronikon” system of GA 55-75 compressor provides all opportunities for remote monitoring
and control. It can be integrated in central governor system and /or connected to a PC running Windows software
providing access and control of all data available in the “ Elektronikon”. On top of all this, add-on modules for extra
digital and /or sensor inputs are available.
3.4.1. Load - No Load
3.4.1.1. Principle
The inlet valve of a Load - No Load (L-NL) compressor is either fully open, either completely closed. When the
compressor has reached the maximum pressure in the air net, it is not stopped but switched to ‘No Load’. This means
the inlet valve closes off completely but the drive motor continues to run. As a result the pressure will not rise
further and too many starts per hour for the motor will be avoided.
Unfortunately a waste of power occurs in NL running condition.
During NL running condition the inlet valve is closed off completely. The air output is reduced to 0%, but the power
consumption remains on a 25% level. (Fig.8)
page 20/42
100 %
75 %
50 %
25 %
0%
Power Capacity Power Capacity
Load No Load
Figure 8: Power and capacity in stabilised L-NL conditions

This is due to the small amount of air which is aspired and compressed to create the minimum pressure at NL.
Although this air volume is very small, the aspiration via the channels bypassing the closed inlet valve creates a
vacuum and causes a very high pressure ratio over the screw element resulting in a power consumption of still 25%
in stabilised NL condition.
On top of that, the power consumption will only gradually decrease proportional to the exponentially decreasing
internal pressure (Fig. 8).
3.4.2. Delayed Second Stop (DSS)

In traditional electro-pneumatic controlled compressors, the motor will continue to run for a fixed amount of time
(e.g. 6 min for 45kW) at each switch-over to NL. This to meet the limitations on motor starts per hour (e.g. 10st/h for
45kW) .
The Elektronikon  regulator implemented on all GA Pack and Full Feature compressors operates according to the
advanced DSS-algorithm which cuts the NL running time to a minimum. The DSS-algorithm will stop the motor as
soon as possible after a switch -over to NL (e.g. 45kW).
If the previous stop occurred at least 6 min ago, the motor will be stopped 30s after the switch-over to NL
(when internal pressure reached 2 bar(a), see section 3.2)
If the previous stop occurred less than 6 min ago, it will delay the second stop until 6 min have elapsed and
then stop the motor immediately.
The DSS-algorithm can realise an important reduction on the NL running time in conditions of intermittent operation
with prolonged stop periods.
3.5. Modulation
3.5.1. Principle
The inlet valve of a compressor regulated by modulation can be closed off partially. This will vary the capacity
between 100% and 50% according to air demand. The drive motor will run continuously, avoiding too many motor
starts per hour.
Unfortunately a waste of power occurs during modulation.
3.5.2. Power consumption

A standard oil-injected screw compressor regulated by modulation, will vary it’s outlet by throttling the inlet valve.
Capacity can be reduced to 50%. Due to throttling, a considerable pressure drop will occur over the inlet valve. As a
result the pressure ratio over the screw compressor element will increase. Therefore the power consumption will not
drop to 50% but remain above 85%, which means a 35% waste of power (Fig.9).
As a result capacity will vary between 100% and 50% whereas power consumption will vary simultaneously but
between 100% and 85%. Below 50% capacity, the compressor switches to No Load condition and similar
phenomena occur as on a purely Load - No Load compressor.
page 21/42
100 %
75 %
50 %
25 %
0%
Power Capacity Power Capacity

Full Load 50% Modulation
Figure 9: Power consumption and capacity during Modulation
3.6. Variable Speed Drive
3.6.1. Principle
A VSD compressor runs continuously with a completely open inlet valve. The air output is varied according to air
demand by increasing/decreasing the speed of the drive motor.
Thanks to the VSD operation, there is no limitation on the amount of motor starts.
Part load or No Load conditions and the related waste of power do not exist. The VSD only consumes power
according to the customer’s air demand.
3.6.2. Operation
The Elektronikon  regulator monitors continuously the outlet pressure and steers the converter. The converter
steers the motor with the appropriate frequency. The motor varies its speed according to the supplied frequency. The
compressor air outlet varies proportionally to the motor speed.
The closed loop system targets a constant delivery pressure equal to the programmed ‘setpoint’.
In practice the pressure remains stable within a +/- 0.1 pressure band.
3.6.3. Power consumption

It is clear from the above that a VSD-compressor only consumes power according to the customer’s air demand.
Part load and/or No Load conditions do not exist. There is no waste of power. Power consumption varies
proportionally with capacity (Fig.10).
100 %
75 %
50 %
25 %
0%
Capacity Power Capacity Power

100% Capacity 50% capacity
Figure 10: Power consumption and capacity during VSD operation
3.7. Conclusion
The VSD regulation solves the original problem of the limitation on the amount of motor starts per hour for which
the two traditional regulation systems Load - No Load and Modulation were developed. Simultaneously it realises
outstanding energy savings and provides a number of additional benefits.
Variable Speed Drive is truly the today’s “state of the art” compressor regulation.
page 22/42
Chapter 4. Basic of dryer
4.1. Drying air principles
4.1.1. Moisture in compressed air systems
4.1.1.1. Composition
Atmospheric air is a mixture of different gases of which the composition is the following:
Nitrogen (N2), 78% Oxygen (O2), 21% and others, 1%.
The “others” consist mainly of Argon (Ar), 0.9%. In addition to this, atmospheric air always contains water in
vapour form.
The amount of water vapour in the air normally varies between 1 and 4%. What determines the possible amount of
water that can be held in vapour form in the atmospheric air is the temperature alone.
The warmer the air is, the more water vapour it can contain.
In Graph 1, we can see the maximum amount of water that can be held by one m³ of air at different temperatures and
pressure. This graph shows the saturation point, after this points dew will immediately start to form.
Saturation of 1 m³ of air
1000.00 450
400
350
100.00
Saturation pressure (mbar)
300
Density (g/m³)
250
10.00
200
150
1.00
100
50
0.10 0
-40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Water Content g/m³ Pressure mbar Temperatures in °C
Graph 2 : Water content in 1m³ of air
page 23/42
4.1.1.2. Understanding air density

In simple terms, density is the mass of anything divided by the volume it occupies. The density of the air depends on
its temperature, its pressure and how much water vapour is in it. In compressed air, the density increases as pressure
increase.
4.1.1.3. Water content

We know now that air contains a certain quantity
of water in a vaporous form at different pressures
and temperatures. By compressing the air
(reducing the volume occupied by it) the water
vapour density rise.
The outlet air of an air compressor is always hot

and 100% saturated with water vapour.
Any further reduction of temperature will cause the formation of water condensation in the outlet piping. (see
graph).
4.1.1.4. Dewpoint
Is the temperature at which a certain amount of water vapour will be equal to the maximum amount of water vapour
the same volume can hold. In other words, it is the temperature at which moisture will condense.
The dewpoint temperature gives a much better estimate of the amount of moisture present in the air.
4.1.1.5. Relative humidity

Ratio of actual water content of one cubic meter of air at a certain g/cm³
temperature and pressure to the maximum water content it physically
can carry at these conditions. The warmer the air is, the more water
it can “hold”. Dewpoint is a measure of how much water vapour is The ability of air
actually in the air. Relative humidity is a measure of amount of water to hold water
in the air compared with the amount of water the air can hold increases with
at the temperature it happen to be when you measure it. (see table 1) temperature
Temperature
Humidity is the amount of water vapour in the air and can be described in different ways, including “relative
humidity” which is the term used most often in weather information meant for the public. Relative humidity is the
amount of water vapour in the air compared with the amount of vapour needed to make the air saturated at the
current temperature of the air.
Air temperature in °C and Water vapour air can hold at this temperature. (Extract of Table 1)
30 ° C 30.38 g/m³ of air
20 ° C 17.30 g/m³ of air
10 ° C 9.34 g/m³ of air
These numbers apply to air at sea level pressure.
4.1.1.6. Pressure dew point and atmospheric dew point
4.1.1.6.1. Dew point:

Is the temperature of a gas at which the vapour in a space (at a given pressure) will start to condense (form dew).
Dew point of a gas mixture is the temperature at which the highest boiling point constituent will start to condense. In
Atlas Copco, we always talk about pressure dewpoint, which is the actual dew point of the compressed air.
4.1.1.6.2. The Pressure Dew point (PDP)

Is the temperature at which water vapour begins to condensate at a given pressure. It differs from the atmospheric
dewpoint because the water vapour is confined in a smaller volume of air when it is compressed.
page 24/42
4.1.1.6.3. The Atmospheric dew point

Is the actual dew point of same air in free condition i.e. expanded to atmospheric pressure. As the volume then
becomes much bigger (when expanding to 7 bar effective pressure to 1 bar absolute = 8 times bigger) the water
content per specific volume unit will be less and consequently the dewpoint.
Example: PDP= 2°C; Water content = 5.6 g/m³; Pressure (effective) = 7 bar
Expansion Pressure (absolute)= 1 bar; water content = 5.6 /8=0.7 g/m³; Atmospheric Dewpoint = 22°C
4.1.1.7. Water vapour in the compressed air system
4.1.1.7.1. Where it comes from

Atmospheric air with a certain water content (depending on the temperature and the relative humidity) is sucked in
the compressor. There it is brought to a higher pressure, a decreased volume and a higher temperature. In spite of
the decreased volume, the water vapour content still remains in vapour form due to the high temperature of the
compressed air. Then the air is brought to the aftercooler where it is cooled to a much lower temperature, resulting
in condensation. The free water is then separated. The compressed air leaving the aftercooler is always saturated
(i.e. 100% R.H.). Therefore if the temperature decreases further more water will condense in the compressed air
system.
4.1.1.7.2. What can happen?

The moisture in a compressed air net causes corrosion of the piping, pneumatic devices and air tools. Corrosion
starts already a 50% R.H. By drying the compressed air, the pressure drops and the air leaks in the air net are
avoided. This reduces the power and capacity requirement of the compressor therefore saves on the functional cost
of the installation. This condensation is not only harmful for the piping system, but it will also reduce the life span
of the condensed air equipment. In some applications, it will also spoil the end product. In all cases is therefore
recommended to install air dryers after the compressor.
Air tools:
Better lubrication
Less maintenance corrosion
tendency
Pneumatic Components:
Longer lifetime
Air nets:
No corrosion relative
No draining humidity
The air net will be cheaper to install 0 50%
Applications:
Spray painting; no damages to finish
Blast cleaning: no clogging or icing
Production:
Less risk of unplanned shutdowns
4.1.1.7.3. Solution
The solution to all these problems and elimination of the cost caused by them is: Drying the compressed air.
4.1.2. Basic of drying compressed air
4.1.2.1. Definitions
Dry compressed air is compressed air with a reduced water vapour content.
page 25/42
4.1.2.2. Methods
4.1.2.2.1. Water Separator

As the air temperature falls in the air net, water vapour in the air condenses. This condensate can be removed from
the air net by a waterseparator. As a waterseparator can only collect water in liquid form, it needs to be placed at the
point in the line where most of the water condenses, that is where the temperature is the lowest. To prevent ice
formation it must be placed where the temperature is somewhat above 0°C. Water separator utilises centrifugal
forces. The air flowing through is given a rotary motion so that the water particles are thrown against the walls of
the container and are thereby separated from the air. This method is used in the air nets close to the point of use to
prevent the water to reaches the tools or process. In order to prevent water to form in the air nets the compressed air
has to be dried at the source.
Drying done in different ways:
4.1.2.2.2. Cooling and refrigeration

The ability of air to retain water is depending on the air temperature and as it decreases with decreased temperature,
cooling is one way of drying. This is done in an aftercooler in which the major part of the content is separated from
the air.
Atlas Copco has both watercooled (HD) and aircooled aftercoolers (TD), matching all Atlas Copco stationary
compressors. Generally, air-cooled aftercoolers are used with aircooled compressors.
When the dew point reached in this way is not sufficient, a refrigeration system is normally used (FD). As the
cooling temperature must not be so low as to allow frost formation on the coils, the dewpoint is normally limited to
between +0.6 and +3°C.
4.1.2.2.3. Aftercooler
Heat exchangers for cooling air or gas discharge from compressors. Designed to reduce the temperature and liquefy
condensate vapours and oil droplets, which are drained off.
The dewpoint obtainable by aftercooling is dependent on the temperature of the coolant (water or air). The
temperature of the compressed air after the aftercooler will be usually some 10°C higher than the coolant
temperature. (Ex: a+10°C means the dewpoint will be 30°C).
As this cooling mostly is not sufficient to avoid further condensation in the compressed air system, further cooling is
necessary. Aftercooling removes approximately ° of the water produced by compressing the air, the remaining ↓ of
water content can be treated with a refrigeration type air dryer (FD).
Aftercooling decreases the volume of air available. However, this represents no real power loss since the air would
in any case be cooled in the pipe system and then the precipitation of moisture and oil would take place in the system
itself with consequent harmful effects.
4.1.2.2.4. Over-compression
This method as such is one of the simples available. The air is compressed to a higher pressure than the final
working pressure. Due to higher pressure, the volume of air is decreased and consequently the concentration of
water vapour is increased. When the air “aftercooled” and “water-separated” is expanded to the working pressure, a
lower dewpoint is obtained. This method is only useful for very small airflows, due to high-energy consumption.
4.1.2.2.5. Absorption
Drying by absorption is a chemical process where the water vapour is bound to the absorption material by a chemical
reaction. Absorption of water can be achieved with both solid (Lithium chloride, calcium chloride) and liquid
(sulphur acid, glycol) adsorbents.
Disadvantages with absorption:
The continuos consumption of the absorbent results in high operating cost.
With this type of dryers, only a dewpoint reduction of maximum 15°C can be obtained.
The drained moisture is corrosive. The lubricant used is very aggressive and not environmentally friendly.
There are no adsorption dryers in the Atlas Copco dryer program.
4.1.2.2.6. Adsorption
Drying by adsorption is a physical process where the water vapour is bound to the adsorption material by molecular
adhesion forces.
This method of drying gives the lowest dewpoint of compressed air (down to –40°C). The compressed air passes
through a tower where the desiccant adsorbs the water vapour in the air. This process continues until the desiccant is
page 26/42
saturated with water vapours. The airflow is then automatically switched to the other tower (with active desiccant).
The same principle is used in CD and MD dryers where part of the drum dries the air whilst the other part is
regenerated. The material is continuously regenerated by hot compressed air (all air is recuperated). As no
additional heating is required the power consumption of the CD and MD dryers is extremely low. In the MD dryer,
the dewpoint is reduced by approx. 50°C. The most common desiccant are the Activated aluminia (Al2O3), standard
in Atlas Copco adsorption dryers, and the Silicagel (SiO2).
4.1.2.2.7. Osmosis
Air is blown through a membrane where the molecules are separated.
4.2. Refrigeration dryers

As refrigeration deals entirely with heat, some knowledge of the nature and effect of heat is required for a better
understanding of this subject. Let us therefore review some of the basics.
4.2.1. What is heat?

Heat is a form of energy.
Since heat is not a substance, it can only be dealt with through its effect on substances for example, via temperature
measurements. Every substance on hearth contains some heat. If water of 40°C is warmer than water of 20°C, it
only means that water of 40°C contains more heat.
The unit of heat is the kcal (kilo-calorie) or the kJ (kilo-joule). 1 kcal is the amount of heat needed to increase the
temperature of 1 kg of water with 1°C
4.2.2. Heat flow

Heat flows from bodies or substances with a higher temperature to bodies or substances with a lower temperature,
just as water flows from a higher level to a lower level.
As water never flows uphill, heat cannot flow from a cold body to a warm body. When two substances of different
heat content are brought together, the heat will flow from the hot to the colder substance until they both have the
same temperature. At this condition, no more heat can flow. The greater the temperature differences between the
two substances, the faster the heat will flow, or the faster the heat exchange will be.
4.2.3. Specific heat

The specific heat of a substance is the amount of heat needed to increase the temperature of 1 kg of that substance
with 1°C. This specific heat is different for each substances.
Some example:
Water: 1.0 kcal/°C/kg
Oil: 0.4 kcal/°C/kg
Cast iron: 0.17 kcal/°C/kg
4.2.4. Boiling Point

At atmospheric pressure (sea level) water boils at 100°C. On top of a mountain, where the atmospheric pressure is
lower, the water boils at a lower temperature, e.g. 85°C.
Deep down in a tunnel, or in a coal mine, where the atmospheric pressure is higher than at sea level, the water will
boil at a higher temperature e.g. 105°C.
As long as the temperature of water (at sea level) remains below 100°C, it will remain a liquid. If more heat is added
to the water, this heat will serve to increase the temperature of the water. The water will begin to boil once it reaches
100°C, i.e. the atmospheric boiling point at sea level. The boiling point always depends from the pressure prevailing
in the liquid.
If more heat is now added, the temperature of the water will no longer increase, instead more water will turn into
vapour. But when no more liquid is available then we will overheat the vapour or gas, and only then will the
temperature increase.
Liquid evaporates if the temperature at a given pressure increases to the boiling point.
The vapour condenses back to liquid if the temperature at this same pressure decreases below the boiling point (or
condensation point). The boiling point it also called the boiling temperature or the boiling pressure. The lower the
pressure on the liquid, the easier it will start to boil.
page 27/42
4.2.5. The principle of evaporation & Cooling

From the theory we know that:
If, in an enclosed volume, the pressure above a liquid decreases then the pressure in the liquid decreases also (both
pressure are the same).
If the pressure in the liquid keeps on dropping, then at a certain stage we will reach the boiling point of this liquid.
From this point onward, if the pressure drops even further, the liquid will start to boil and evaporate at an increasing
rate.
In the course of the expansion process, during which liquid Freon R404A gradually changes into saturated vapour, a
pressure drop from 5 to 1 bar causes a considerable temperature drop: The Freon mixture (liquid/vapour) cools
down from 0°C to –45°C. This temperature drop will cool down the compressed air in the heat exchanger to a
temperature of +3°C.
4.2.7. Main dryer components

• Water separator with automatic drain ensures optimum condensation drainage
• IP54, TEFC, fan motor on all 3-phase units
• Large capacity condensers to convert refrigerant gases
• Constant Pressure Expansion valve
4.2.8.1. Air Circuit

Incoming compressed air (A) is pre-cooled in the air-to-air heat exchanger (B); passes through the air-to-refrigerant
heat exchanger (C) where it’s cooled down to +3°C. The condensate is separated from the air and automatically
drained by the water separator (D). Before leaving (E) the cold dry air passes for a second time through the air-to-air
heat exchanger to be reheated.
4.2.8.2. Refrigerant circuit
4.2.8.2.1. Overlook
From the compressor (F) the refrigerant gas comes in the condenser (G) where it is cooled by a high volume air
cooling fan or cooling water and becomes liquid. A pressure regulated expansion valve (H) regulates the airflow
into the air-to-refrigerant heat exchanger ( C ) where the refrigerant evaporates by extracting heat from the
compressed air. The refrigerant pressure is then increased in the compressor and the cycle starts again.
page 28/42
4.2.8.2.2. The Complete Freon Cycle

Let us take a simple example in order to explain the principle of application. Imagine a receiver with liquid Freon
R404A, at 6 bar(a) and 0°C. (This Freon, therefore, is at its boiling point). Let us now expand the 6 bar(a) to a
pressure of 1 bar(a). The Freon will begin to boil and turn into vapour. The heat needed for this is given up the
Freon itself. We thus obtain strong cooling of the Freon.
After passing a restrictor, to come down to 1 bar(a), the expanded Freon will cool down to an impressive –45°C.
Again, this effect is typical for Freon.
Freon was invented specifically for the purpose of obtaining a strong cooling after expansion. This phenomenon is
used widely in industrial cooling applications, air conditioners, household refrigerators etc.
All types of Freon have a typically low boiling pressure. The boiling temperature of Freon is also comparatively low
for any relevant given Freon pressure. The process extracts heat from the compressed air, and this heat warms up the
Freon vapour.
(remember: heat always flows from a warm body to cold body).
Notice that the Freon pressure, after the start of expansion, remains constant, 6 bar(a) at 2”C. This line forms an
isobar. The specific heat content however increases as the saturated vapour extracts more and more heat from the
medium being cooled (e.g. compressed air). This heat will evaporate more and more liquid Freon. An initial
mixture of e.g. 80% Freon liquid & 20% Freon vapour will gradually change into 0% liquid & 100% vapour. At this
point no more liquid is available. The Freon vapour, created after expansion, will usually serve to cool another
medium e.g. compressed air. This is done with the help of a heat exchanger
The evaporation of liquid Freon occurs all the while at a constant temperature (isotherm). Therefore , at this point,
the heat flowing from the compressed air to the Freon serves to transform liquid Freon into saturated Freon vapour
(basically a process of evaporation).
When no more liquid Freon is available for evaporation, the heat transferred from the medium (compressed air) will
immediately begin to raise the temperature of the Freon vapour. The condition of the vapour is now no longer
“saturated”. The extra heat warms up the Freon vapour which is now called “overheated” or “superheated”. The
temperature of the Freon vapour/gas will now typically rise from +2°C to + 1 O°C.
We say that the Freon gas is superheated by 8°C (temp. rise from 2°C to 1 O°C). The heat exchanger in which the
expanded Freon evaporates is called, quite logically, the evaporator or heat exchanger.
You should be aware that Freon is a rather dangerous gas. It pollutes our atmosphere. It is also an expensive gas. It
cannot be simply expanded and blown off to the atmosphere. We have to recuperate it use it again. In order to
recycle the Freon gas we shall compress it again after evaporation by means of a Freon compressor.
As a rule, a compressor can only compress gas, not liquid. We must ensure then that the Freon returned from the
evaporator to the compressor consists of Freon gas only. All liquid Freon must have evaporated before entering the
Freon compressor. The Freon therefore must be overheated (“superheated”). This to prevent liquid knock in the
Freon compressor.
In our example, the overheated Freon gas undergoes adiabatic compression, in the Freon compressor. We shall
increase the pressure from 6 bar(a) to 18 bar(a). During compression, the heat content of the Freon gas builds up
because of the heat of compression. This heat will have to be removed after compression, in order to revert to the
desired condition of liquefied Freon at high pressure. We use a special cooler for this, Hot Freon gas always needs
to be condensed back to liquid. The cooling device that we use for this is called, quite logically, a condenser.
We have seen that after compression, both the temperature and pressure of the Freon gas are high: 80°C at 18 Bar(a).
It is the heat that we want to get rid of now. By cooling down the overheated Freon gas (while maintaining high
pressure) will bring it down to its condensation point (or boiling point). The superheated gas will cool down and
reach the state of saturated gas. It now begins to liquefy. We are looking at a temperature drop from 80°C down to
40°C..
If more heat is removed from the saturated gas it will not cool down further (yet): The additional heat removed will
only cause more saturated vapour to condense back into liquid, until all the Freon has reverted to the 100% liquid
state.
If we now cool down further, then more heat is removed from the liquid. This will cause a temperature drop from
40°C to e.g. 35°C. The latter condition (35°C) is called subcooling (“undercooling”). The liquid has been
undercooled by 5°C (from 40°C to 35°C).
It soon becomes apparent, that we also need to establish a well defined flowrate of the Freon, in order to meet
various operating conditions. Looking at an FD dryer, let us take at a few examples-.
Example 1
In the case of e.g. low air consumption only a small amount of compressed air needs cooling in the evaporator.
Consequently the Freon will only warm up slightly and not all of it will evaporate. In principle this could ultimately
result in saturated vapour (and possibly some liquid) being sucked into the Freon compressor. This would create the
risk of destructive liquid knock. It follows that the amount of Freon, delivered to the evaporator, needs to be
page 29/42
metered so as to ensure the return of overheated gas only, to the Freon compressor. We obtain this effect through the
use of an adjustable flow restrictor.
Example 2
But if large amounts of compressed air are to be cooled in the evaporator, then a small Freon flowrate would soon
cause all the Freon gas to evaporate and subsequently the Freon gas would become too hot. Hot gas sucked into the
Freon compressor would be heated up even further by the heat of compression. This would cause overheating of the
Freon compressor. To avoid such a risk we need to circulate more Freon capable of absorbing the extra heat.
What we need in fact is an adjustable restrictor with one setting adapted to span the specific cooling range required.
Such a device should result in a fixed flowrate of Freon. This will result in a scale of evaporation which will match
the varying conditions of heat load, while also protecting the compressor against overheating. Such a system will
ensure stable operation. The device which we use to adjust and monitor the flowrate is called an expansion valve.
We know now that the condition of the Freon vapour after the expansion valve needs to be monitored continuously.
In older designs this condition was monitored mainly through the use of a temperature sensor placed after the
evaporator. This was not a very accurate method for controlling the response of the expansion valve. Dewpoint
fluctuations were rather common.
In later designs we introduced a much improved system whereby we monitor Freon pressure in or before the
evaporator. FD dryers, during the last 1 0 years or more, have been equipped with such constant pressure expansion
valves. These provide stable performance, resulting in a constant dewpoint. The setting of such a valve creates a
certain throttling or closing of the expansion valve mechanism. This will yield a very stable Freon outlet pressure,
even with reasonable variations in Freon inlet pressure. How does this valve work ?
“Constant pressure” expansion valve - its purpose.
The expansion valve reduces the pressure of the liquid Freon. This will cause evaporation: the transition of an
amount of liquid to saturated vapour. During this transition, the Freon pressure and temperature drop significantly.
The heat content however remains constant. No energy is being demanded or added during expansion, so no heat is
added or removed during this process. While the pressure is dropping, the liquid will start to boil (when boiling
point is reached). The necessary heat required for boiling or evaporating is obtained from the liquid itself. It is this
which causes the sudden temperature drop.
Downstream of the expansion valve, we will have a mixture of liquid Freon and Freon vapour. We rarely know what
the exact ratio of the mixture will be, But we do know that this ratio will change, depending on the (varying) amount
of heat given off by the compressed air.
The “constant pressure” expansion valve
Will maintain a constant Freon outlet pressure in face of a varying heat load (e.g. fluctuations in compressed air
consumption). This guarantees a constant dewpoint of the FD dryer under all working conditions (within AML
limits).
“Constant pressure” expansion valve - Build up and location.
A constant pressure expansion valve is basically pressure regulating device, responding to the pressure at the valve
outlet. It is ;Installed at the evaporator inlet side as a device to control the Freon refrigerant flow. The expansion
valve meters refrigerant to maintain a constant evaporator pressure during dryer operation.
This type of valve consists of a diaphragm, a control spring (1) and the basic valve needle (or ball) and seat (2). The
control spring is above the valve diaphragm, exerting force to move the diaphragm downwards, which is the opening
direction of the valve. The opposing force on the opposite side of the diaphragm is developed by the low side
(evaporator) pressure. This force tends to close the valve.
“Constant pressure” expansion valve - How exactly does it work.
During shutdown of the FD dryer, the valve will be closed as evaporator pressure builds up and overcomes the
control spring pressure. When the FD dryer is started up, the compressor quickly reduces the pressure on the suction
side (in the evaporator). When this pressure reaches that of the control spring the valve is ready to open. It actually
opens when the LP Freon (evaporator) pressure is reduced just below the control spring setting.
This is the valve opening point. The valve, however, must open further to satisfy the compressor capacity at the set
operating pressure.This occurs as the operation of the compressor further reduces the LP Freon pressure (in the
evaporator). LP Freon pressure continues to drop, and the valve continues to open until a point is reached where
liquid is entering the evaporator coil and vaporising at a rate equal to the Freon compressor pumping capacity.
Evaporator pressure now stabilises and the system will operate at this point for the remainder of the running cycle.
Constant pressure expansion valves feature a manual adjustment (4). The adjusting screw increases or decreases the
tension of the control spring above the diaphragm, changing the valve opening point. The valve can be adjusted to
open at a predetermined pressure within the design range of the spring. The valve operating point will be a fraction
below the opening point. The exact differential is determined by the Freon compressor pumping capacity. The
operating pressure (evaporator pressure) can be observed on a Freon LP pressure gauge attached to a system.
page 30/42
4.3. Adsorption dryers

PNEUMATIC DIAGRAM
A: Tower A
AF: Air filter
B: Tower B
CA: Control air valve
IV: 3-way valve
OV: Outlet valve (= nozzle valve)
P1: Pressure gauge 1
P2: Pressure gauge 2
PA: Pneumatic actuator
PR: Pressure regulator
(only for 16 bar units)
PV: Pneumatic valve
S: Silencer
SV: Solenoid valve
TV: Throttle valve
Figure 11: Shows the pneumatic diagram of the dryer
4.3.1.1. Description
The construction of the air dryer is simple, reliable and easy to service. The dryer has two towers containing the
adsorbing material or desiccant. This desiccant is a very porous grain material which can adsorb large amounts of
water vapour.
The operation cycle of the dryers is repetitive and is controlled by a factory-set timer. While the desiccant in the first
tower dries the compressed air, the desiccant in the second tower is being regenerated and vice versa. Regeneration
of the desiccant is achieved by means of purge air from the drying tower.
The compressed air entering the dryer is led to one of the towers by means of the inlet valve. The position of the
inlet valve depends on the condition (activated or not) of the solenoid valves. As the air flows upwards through the
tower, the desiccant adsorbs the water vapours and the compressed air is dried. Once the top of the tower is reached,
the air leaves the dryer via the outlet valve (= nozzle).
A small portion of the dried air does not leave the dryer immediately via the nozzle valve but is expanded to
atmospheric pressure and flows downwards through the other tower, regenerating the desiccant.
This regenerating air is finally released via the solenoid valve and the silencer. These solenoid valves are controlled
by the timer. After a certain period, the cycle will restart. The fully regenerated tower will now dry the air whereas
the other tower will be regenerated. The condition of the desiccant can be checked by means of the moisture
indicator. !
4.3.2. Main dryer components
CD dryers CD 7 - 60
page 31/42
(1) Head and Base.

Aluminium die casted parts to connect the dryer’s in and outlet, the control devices
and which contain the shuttle and nozzle valve.
(2) Towers -
Aluminium tubes of different diameter and length. These dimensions are one of the
factors that define the capacity of the dryer.
(3) Strainers:
Stainless steel perforated plates which are kept on their places by means of stainless
steel clamps (17).
(4) Desiccant:
Activated alumina (AL203 )size F200, this type of desiccant is different from the
desiccant used in our previous and current types of BD and CD dryers. The desiccant
is fixed between the strainers on bottom and on top. These heads (1) towers (4) with
strainers (3) and desiccant (4) are assembled together by means of threaded rods.
(5) Shuttle valve.

The shuttle valve is located in the base, which is the inlet part of the dryer. This valve is an assembly of the piston (1
2) with 0 rings, shafts (1 5) and exhaust washer (16) on both sides of the piston. This shuttle is gliding in the valve
seats (1 1) which are provided with 0 rings to avoid leakage.
(6) Nozzle valve:

The nozzle valve is located in the head, which is the outlet part of the dryer.
The nozzle valve is an assembly of the piston (12, the same as on the shuttle valve) two pipes (1 3) and a calibrated
nozzle (1 4). This valve is also gliding in valve seats (1 1).
(7)(8) Timer and solenoid valves

An electronic timer controls the solenoid valves, one for each tower. It opens, in turn one solenoid valve and kept
the other closed. (see working for details).
(9) Silencers:
Silencers are placed on the outlet of the solenoid valves to reduce the noise of the expanding air during switching
over the towers.
(10) Indicator:
The indicator gives a rough indication of the performance of the dryer. Blue shows a dryer which is working good,
whereas a pink indication shows a dryer which need to be regenerated.
(11) Valve seat:

with 0 ring ( 4 pieces 1 dryer).
(12) Piston: with 0 ring ( 2 pieces 1 dryer).
(13) Pipe:
Self-cleaning channel for purge air.
(14) Nozzle:
Calibrated orifice for purge air
(15) Shaft:
Stainless steel shaft to carry the exhaust washer.
page 32/42
(16) Exhaust washer:

These washers have the purpose to assure and speed up the movement of the Piston into the correct position.
(17) Strainer clamp

To keep the strainers and the desiccant in position.
(18) 0 ring:
To seal the towers and the head and the base.
(19) Seal plug:

To seal the different chambers of the head and the base.
(20) Connection plug –

The 0 rings are needed since the thread of this plugs is cylindrical. The internal thread is either “G” or “NPT”. It
will be also possible to connect our own made filters directly onto the dryer.
CD dryers CD 100 - 230
(2) Towers:
Welded vessels of different diameter and length. These dimensions are one of the factors
which define the capacity of the dryer.
(3) Strainers:
Welded stainless steel perforated plates, in bottom and on top, which keep the desiccant
on its place (4).
(4) Desiccant:
Activated alumina (AL2O.) size F200 this type of desiccant is different from the
desiccant used in our previous and current types of BD and CD dryers.
(5) Way inlet valve -

The valve is located at the bottom, where the iniet of the dryer is. This valve is an
assembly of a 3 way valve and a pneumatic actuator.
(6) Outlet valve:

The outlet valve is located in the top, of the dryer. It has the purpose of a shuttle valve and it has also the purge
nozzle.
(7)(8) Timer and solenoid valves:

An electronic timer controls the solenoid valves, one for each tower. It opens, in turn one solenoid valve and kept
the other closed. (see working for details).
(9) Silencer:
A silencers is placed on the outlet of the pneumatic valves to reduce the noise of the expanding air during switching
over the towers.
page 33/42
(10) Indicator:
The indicator gives a rough indication of the performance of the dryer. Blue shows a dryer which is working good,
whereas a pink indication shows a dryer which need to be regenerated.
(14) Nozzle:
Calibrated orifice for purge air.
(21) Control valve:

To isolate the pneumatic system from the compressed air net.
(22) Filter:
Air filter to remove the dust of the desiccant, for the control air.
(23) Pressure regulator:

Only on the 16 bar versions a pressure regulator is needed, since the maximum working pressure of the pneumatic
valve is 1 0 Bar.
(24) Needle valve:

Valve to adjust the speed of the pneumatic valve.
(25) Pneumatic valve:

Since the solenoid valves are to small to cope with the big air flow, pneumatic valves are used.
(26) Gauge:
Pressure gauges to indicate the pressure in each tower.

Working principle
4.3.3.1. CD 7 - 60
• solenoid valve a is open ( at start-up both solenoids are
closed)
• pistons of shuttle and nozzle valve close tower A
• desiccant of tower B is adsorbing the water vapour out of
the passing air.
• dry air leaves the CD dryer, passing the outlet valve seat
and the moisture indicator
• a small amount of the dried air flows to tower A via the
self cleaning nozzle
page 34/42
• this dry air regenerates the desiccant from tower A

• the wet air leaves the CD dryer via solenoid valve A and the silencer which reduces the noise of the
expanding and purge air.
• the timer controls the switching of the solenoid valves and these valves change the function of the
towers form adsorbing to regenerating.
4.3.3.2. CD 100 - 230

• pneumatic valves are closed
• air is passing the 3 way valve into tower A where the desiccant adsorbs the moisture out of the air
• the outlet valve closes the port B, the nozzle in this permits a small flow of dried air to pass through
tower B to regenerate the desiccant in this tower
• dry control air is taken from the outlet. ( regulator only on 16bar units)
• the solenoids which are controlled by the timer, supply control air to the pneumatic valves and the
pneumatic actuator of the 3 way inlet valve
• the open pneumatic valve controls the purge air by bleeding it through a silencer to atmosphere.
page 35/42
Chapter 5. Filtration Principles
5.1. Basic filtration

Most production processes demand pure compressed air ( no moisture, no particles, no oil) -for
example: in the pharmaceutical, food and beverage industries; pneumatic instrumentation;
assembly of electronic components, handling of hygroscopic materials or outdoor installations
with freezing temperatures.
Generally, compressed air carries some moisture. An after-cooler linked-up with a water
separator will remove most of the water, but not all of it. Remaining moisture can cause
considerable damage to your compressed air system and spoil your end products. To avoid this
problem, you need pure compressed air.
To fulfil the needs of compressed air users, Atlas Copco offers a variety of dryers and filters to
keep compressed air systems clean, corrosion-free and to protect users' processes and products
against contamination.
Dryers and filters offer you:

- save the end products against spoilage
- protects the air net and tools
- low installation costs
- reliable in operation
- low power consumption
- minimum maintenance
- sure, safe performance
- favourable cost/efficiency ratio
5.1.1. How do they work?

The key to effective filtration is to optimise the three mechanisms of filtration, i.e.
Direct interception (removal of larger particles)

inertial impaction (removes particles which are unable to negotiate the tortuous path between the
fibres).
Diffusion or brownian movement (which causes the very small particles to eventually collide
and adhere to a fibre)This is achieved by using a deep bed of borosilicate microfibre
material, which ensures that liquid and solid particles as small as 0.01 micron can be
removed. Another important advantage of the microfibre is that the larger free space
within the filter material allows high flow rates, ensures low-pressure drops and a long
service life.
Fine oil mist removed from the air stream gradually coalesce to form larger droplets. To prevent their carry-over
or re-entrainment, there is an anti re-entrainment barrier on the downstream side of the element. The oil and
water droplets are adsorbed within this barrier and pass down through its cellular structure, forming a wet
band at the bottom of the element. The oil and water emulsion drips from the element into a turbulence free
zone at the base of the filter body, where it is drained away automatically.
5.2. Compressed air quality

Compressed air is used either as a carrier medium for the transport of energy to the point of use. Where its potential
and kinetic energies can be converted into a driving force for pneumatic equipment, or as a process medium itself
(e.g. breathing air) or for processing purposes (agitating, mixing, packaging, conveying and pressurising). For most
applications of compressed air, a requirement of air quality exists, expressible as a permissible level of contaminants.
Compressed air quality classes for solids, water and soils are given in Table 6, in accordance to ISO 8573.
Quality Dirt water pressure oil mg/m³
page 36/42
Class particle size (um) dewpoint ( °C ) at 7 bar

1 0.1 -70 0.01
2 1 -40 0.1
3 5 -20 1
4 40 3 5
5 - 7 25
6 - 10 -
Table 8 : the quality air classes
To specify the quality class for a particular application, quote the three classes in turn, eg.
Quality class 2.2.2. is dirt particle size 1 um, water pdp –40°C, oil content 0.1 mg/m³.
Refer to table 2 for quality recommendations for typical applications.
Typical quality classes

Application Solids Water Oil
Air agitation 3 5 3
Air bearings 2 2 3
Air gauging 2 3 3
Air motors, heavy 4 4-1 5
Air motors, miniature 3 3-1 3
Air turbines 2 2 3
Boot and show machines 4 4 5
Brick and glass machines 4 4 5
Cleaning of machine parts 4 4 4
Construction 4 5 5
Conveying, granular products 3 4 3
Conveying, powder products 2 3 2
Fluidics, power circuits 4 4 4
Fluidics, sensors 2 2-1 2
Foundry machines 4 4 5
Handling of food, beverages 2 3 1
Industrial hand tools 4 5-4 5-4
Machine tools 4 3 5
Mining 4 5 5
Packaging and textile machines 4 3 3
Photographic film processing 1 1 1
Pneumatic cylinders 3 3 5
Precision pressure regulators 3 2 3
Process control instruments 2 2 3
Rock drills 4 5-2 5
Sand blasting - 3 3
Spray painting 3 3-2 3
Welding machines 4 4 5
Workshop air, general 4 4 5
Table 9: Quality classes recommendation for some typical applications
The demand of air purity for high precision complex and fully automated pneumatic systems, and of chemical,
biochemical, electronic, pharmaceutical and food processing applications increase year by year, requiring a
continuously improving level of air treatment.
Research indicates that contamination to the extent of 190 million dirt particle per cubic meter (even more in heavily
industrialised areas) is commonplace. As much as 80% of these particles are smaller than 2 microns and pass straight
through a compressor intake filter. This contamination is supplemented by water vapours and unburned
hydrocarbons from aviation, industrial and domestic heating and vehicle fuels. When this poor quality of air is
compressed, the particle content increases to an excess of 1 billion particles per cubic meter.
page 37/42
5.3. Basic filter types
Atlas Copco has three basic industrial model filters i.e., DD, PD and QD.
DD and PD filters are equipped as standard with a differential pressure indicator or gauge to allow element
replacement in due time. Quick element change is simple only by unscrewing the filter bowl.
5.4. DD filter – General purpose protection

- Particle removal down to 1 micron
- Removal of liquid water and maximum remaining oil content of 0.5 mg/m3 (0.5ppm)
at 21C (70F) Air flow inside to out: coalescing filter (Air flow outside to in: dust
filter)
- Sealant: Epoxy resin forms a seal preventing any bypass of the filter media by the
compressed air.
- Stainless steel screens: Support the microfibre medium, both in- and outside, ensuring
resistance to high pressure shock loads and pulsating air flows.
- Support fabric: Prevents fibre migration and acts as integral pre-filter.
- Coalescing medium: Deep bed of graded density borosilicate micro-fibre removes bulk
contamination in heavily contaminated systems.
- 'O' ring: Special material, resistant to both mineral and synthetic oils. Figure 12: DD Filter
- Anti re-entrainment barrier.: Resistant to attack by acidic, mineral and synthetic lubricants. Prevents
separated liquids from re-entering the compressed air system.
- Wet band: Coalesced liquid is separated from the air stream in the quiet zone formed at the base of the filter.
This is then automatically drained away.
Nominal working pressure 7 bar(e) (102 psig)
Maximum working pressure with automatic drain 16 bar(e) (232 psig)
Maximum working pressure with manual drain 20 bar(e) (290 psig)
Maximum air inlet temperature 66°C (151°F)
Minimum air inlet temperature 1.5°C (35°F)
Initial pressure differential 0.085 bar (1.25 psi)
Initial saturated pressure differential 0.14 bar (2.0 psi)
Recommended element replacement at pressure drop 0.5 bar (7.25 psi) or yearly
Table 10: Specifications DD filter
5.5. Type PD - High efficiency

Particle removal down to 0.01 micron and maximum remaining oil content of 0.01 ppm at
21°C.
Air flow inside to out: coalescing filter (Air flow outside to in: dust filter)
- Sealant: Epoxy resin forms a seal preventing any bypass of the filter media by the
compressed air.
- Stainless steel screens: Support the microfibre medium, both in- and outside, ensuring
resistance to high-pressure shock loads and pulsating air flows.
- Support fabric: Prevents fibre migration and acts as integral pre-filter.
- Coalescing medium.: 96 % voids volume pure borosilicate glass microfibre filter
media. Ensures a high flow rate, quick drainage and low-pressure drop.
- 'O' ring.: Special material, resistant to both mineral and synthetic oils. Figure 13: PD Filter
- Anti re-entrainment barrier: Resistant to attack by acidic, mineral and synthetic
lubricants. Prevents separated liquids from re-entering the compressed air system.
- Wet band: Coalesced liquid is separated from the air stream in the quiet zone formed at the base of the filter.
This is then automatically drained away.

page 38/42

Initial pressure differential 0.1 bar (1.25 psi)
Initial saturated pressure differential 0.2 bar (2.0 psi)
Recommended element replacement at pressure drop 0.5 bar (7.25 psi) or yearly
Table 11: specifications PD Filter
5.6. Type QD- Oil vapour and odour removal

Removal of oil odours and vapours. Max. remaining oil content of 0.003 ppm at 21°C.
- Deep bed of activated carbon granules: Adsorbs oil vapours and odours. Long life span
reduces operating costs (1000 hours at recommended inlet temperature)
- Audible alarm.: Gives warning when dismantling attempted under pressure.
- High efficiency PD coalescing filter
- Automatic drain: Removes separated liquid from filter, ensuring maintenance-free
operation..
- Test valve: A pressure relief valve allows the unit to be depressurised before
dismantling and can also be used for a simple check that the automatic drain is
functioning correctly. (Except for DD/PD/QD6).
- Layer of microfibre filter material: Prevents activated carbon dust carry-over.
- Simple "bolt together" design: Easy connection of filters in series. No interconnecting
pipework reduces installation costs.
- Unique flow designed head: provides smooth air flow and low pressure drop
- Heavy duty screw thread and ribbed bowl.: Allows easy removal for quick element Figure 14: QD Filter
changes.
- Sight glass.: Allows visual check of liquid collection and drain operation.
. Filter models QD 6-85 are two-stage combination units incorporating both PD and QD filter elements. It is essential
that models QD170-QD500 are protected upstream by a separate PD model.
Why QD filter does not have a pressure gauge?
The QD is an activated carbon bed that adsorbs oil vapours, it must always be preceded by a PD to ensure no dirt
particles enter. Dirt particles would block the filter reducing its adsorbent capability . The QD absorbs oil vapours
and as it cannot be regenerated it has a certain lifetime after which it must be thrown away (regeneration is very
difficult). The lifetime is of course is dependent on the amount in vapour phase present in the compressed air stream,
which is related to the temperature of the compressed air. The preceding PD will remove liquid plus aerosols but not
vapours.

Pressure drop over filter at nominal flow and nominal working pressure:
QD6-85 0.3 bar (4,35 psi)
QD170-500 0.07 bar (1.0 psi)
Recommended QD element replacement at 21°C inlet temperature 1000 hours or yearly
Table 12 : Specification QD filters
page 39/42
Table of Contents
Chapter 1. Air________________________________________________________________ 2
1.1. Oxygen (O2): ________________________________________________________________________ 2
1.2. Nitrogen (N2):________________________________________________________________________ 2
1.3. Reference tables ______________________________________________________________________ 2
Chapter 2. Free air delivery (F.A.D.) _____________________________________________ 3
2.1. Concept: ____________________________________________________________________________ 3
2.2. Standard/ Normal Volume Flow Rate ___________________________________________________ 3
2.3. Inlet Volume Flow Rate (Im3/min or Icfm)_______________________________________________ 3
2.4. Actual Volume Flow Rate (Acfm) _______________________________________________________ 4
2.5. Correction calculation – site conditions other than reference ________________________________ 5
2.5.1. Temperature Corrections _____________________________________________________________ 5
2.5.2. Relative humidity ___________________________________________________________________ 5
Correction for Altitude operations _____________________________________________________________ 7
2.6. Noise level measurement _______________________________________________________________ 8
2.6.1. Definitions _________________________________________________________________________ 9
2.6.2. Hitachi Code _______________________________________________________________________ 9
2.6.3. Cagi-Pneurop ______________________________________________________________________ 9
2.6.4. PN8NTC2.2 _______________________________________________________________________ 9
Chapter 3. Compressor Range _________________________________________________ 10
3.1. Piston Principles ____________________________________________________________________ 10
3.1.1. Basic build-up _____________________________________________________________________ 10
3.1.2. Main compressor components ________________________________________________________ 11
3.1.3. Flows and circuits __________________________________________________________________ 12
3.2. Scroll principles _____________________________________________________________________ 13
3.2.1. Basic build-up _____________________________________________________________________ 13
3.2.2. Main compressor component _________________________________________________________ 14
3.2.3. Flow and circuits ___________________________________________________________________ 15
3.3. Screw principle _____________________________________________________________________ 15
3.3.1. Basic build-up _____________________________________________________________________ 15
3.3.2. Main compressor component _________________________________________________________ 15
3.3.3. Flow and Circuit ___________________________________________________________________ 17
3.4. Control/regulation system and instrument panel _________________________________________ 20
3.4.1. Load - No Load ____________________________________________________________________ 20
3.4.2. Delayed Second Stop (DSS) __________________________________________________________ 21
3.5. Modulation _________________________________________________________________________ 21
3.5.1. Principle _________________________________________________________________________ 21
3.5.2. Power consumption_________________________________________________________________ 21
3.6. Variable Speed Drive ________________________________________________________________ 22
3.6.1. Principle _________________________________________________________________________ 22
3.6.2. Operation_________________________________________________________________________ 22
3.6.3. Power consumption_________________________________________________________________ 22
3.7. Conclusion _________________________________________________________________________ 22
Chapter 4. Basic of dryer ______________________________________________________ 23
4.1. Drying air principles _________________________________________________________________ 23
4.1.1. Moisture in compressed air systems ____________________________________________________ 23
4.1.2. Basic of drying compressed air _______________________________________________________ 25
4.2. Refrigeration dryers _________________________________________________________________ 27
page 40/42
4.2.1. What is heat? ______________________________________________________________________ 27

4.2.2. Heat flow _________________________________________________________________________ 27
4.2.3. Specific heat_______________________________________________________________________ 27
4.2.4. Boiling Point ______________________________________________________________________ 27
4.2.5. The principle of evaporation & Cooling _________________________________________________ 28
4.2.6. Basic build-up _____________________________________________________________________ 28
4.2.7. Main dryer components ______________________________________________________________ 28
4.3. Adsorption dryers ___________________________________________________________________ 31
4.3.1. Basic build-up _____________________________________________________________________ 31
4.3.2. Main dryer components ______________________________________________________________ 31
Chapter 5. Filtration Principles _________________________________________________ 36
Basic filtration _______________________________________________________________________________ 36
5.1.1. How do they work? _________________________________________________________________ 36
5.2. Compressed air quality _______________________________________________________________ 36
5.3. Basic filter types _____________________________________________________________________ 38
5.4. DD filter – General purpose protection __________________________________________________ 38
5.5. Type PD - High efficiency _____________________________________________________________ 38
5.6. Type QD- Oil vapour and odour removal ________________________________________________ 39
Table of Content _____________________________________________________________ 40
page 41/42
INDEX
Acfm, 3 Minimum pressure vessel, 15
Adsorption, 26, 30 Modulation, 20, 21
Aftercooler, 13, 15, 25 Moisture, 22
Air, 1, 11, 12, 13, 14, 15, 23, 24, 26, 27, 33, 37, 38 Motor Protection, 17
Air receiver, 13, 14 Motors, 13, 18, 19, 37
Altitude, 1, 2, 4, 18 NEMA, 19
Altitude operations, 6 Nitrogen, 1, 2, 22
Capacity, 6 Noise level, 7
Power consumption, 7 Non return valve, 15
Belt, 13 Oil
Boiling Point, 26 cooler, 16
By-pass valve, 16 filter, 16
Cagi-Pneurop, 7, 8 stop valve, 16
Condensation, 23, 24, 25, 27, 28 sump, 16
Control valve, 33 Oil-free, 9, 12
Desiccant, 31, 33 Osmosis, 26
Dewpoint, 23, 24, 29 Piston, 9, 32
Atmospheric Dewpoint, 24 PN8NTC2.2, 8
Pressure Dewpoint, 24 Refrigerant, 16
Displacement, 2, 11, 14 Refrigeration dryers, 26
Dryer, 13, 16, 22, 25, 26, 27, 29, 30, 31, 32, 33, 34 regulation system, 19
Electric Motor, 17 Relative humidity, 2, 4, 23
Elektronikon, 16, 19, 20, 21 Scroll, 12, 13
Evaporation, 27, 28, 29 Service Factor, 19
F.A.D.. See Free Air Delivery Setpoint’, 21
Filter, 13, 14, 15, 16, 33, 36, 37, 38, 39 Solenoid valves, 30, 31, 33, 34
Filtration, 36 SOUND, 8
Free air delivery, 2 Free field, 8
Freon R404A, 27, 28 Intensity, 8
Frequency, 19 Power level, 8
Gas, 1, 2, 3, 9, 11, 23, 25, 27, 28, 29 Pressure, 8
Hitachi Code, 8 Pressure level, 8
IEC 529, 17 Strainers, 31, 33
Inlet Volume Flow Rate, 2 Temperature, 4, 18
Insulation Class, 18 Limits, 18
IP codes, 17 VSD, 21
ISO 1217, 2, 4 Water content, 23
ISO 2151, 8 Water Separator, 25
ISO 8573, 37 Water vapour, 24
Load - No Load, 19, 20, 21 Windings, 18
Lubrication, 13, 14, 24
page 42/42

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Basic Product Training

1.1. Oxygen (O2):

1.2. Nitrogen (N2):

1.3. Reference tables

Constituent0 Per cent by volume Per cent by mass

Chapter 2. Free air delivery (F.A.D.)

2.2. Standard/ Normal Volume Flow Rate

2.3. Inlet Volume Flow Rate (Im3/min or Icfm)

2.4. Actual Volume Flow Rate (Acfm)

2.5. Correction calculation – site conditions other than reference

2.5.1. Temperature Corrections

FAD ×  1  × (273 + Ambient Temp.)

Example of a different Temperature:

Site conditions FAD:

2.5.2. Relative humidity

FAD (dry air)

Temp pS ρW Temp pS ρW Temp pS ρW Temp pS ρW

-35 0.2233 0.2032 -5 4.015 3.246 25 31.67 23.05 55 157.5 104.4

-30 0.3798 0.3385 0 6.108 4.847 30 42.43 30.38 60 199.2 130.2

-25 0.6323 0.5521 5 8.719 6.197 35 56.24 39.63 65 250.1 161.2

-20 1.032 0.8835 10 12.27 9.399 40 73.78 51.19 70 311.6 198.1

-15 1.652 1.387 15 17.04 12.83 45 95.86 65.50 75 385.5 241.8

Table 3 : Saturation Pressure ps and Density ρw of water vapour at

2.5.3. Correction for Altitude operations

2.5.3.1.2. Influence of pressure ratio Table 4: Air pressure (Absolute)

2.5.3.2. Power consumption and Altitude operations

Reduction factor for shaft input at altitude operation

The compressor will consume less power at a higher altitude…

2.6. Noise level measurement

Table 5: Sound power and power level

FREE FIELD: A sound field in a homogeneous, isotropic medium free of boundaries.

2.6.2. Hitachi Code

Chapter 3. Compressor Range

3.1. Piston Principles

3.1.1. Basic build-up

Figure 1: Typical Single Stage LE/LF compressor

Figure 2: Inlet Valve

3.1.2. Main compressor components

Figure 3: Air flow and regulating system

3.1.3. Flows and circuits

3.2. Scroll principles

3.2.1. Basic build-up

Figure 4: Scroll Compressor element

Figure 5 : Working principle of the Scroll element

3.2.2. Main compressor component

Air intake filter

Instrument panel and controlling/regulating system

Integrated refrigeration dryer

The integrated refrigeration dryer has the following characteristics:

3.2.3. Flow and circuits

3.3. Screw principle

3.3.1. Basic build-up

The injection is usually accomplished by using the discharge pressure. Sometimes a

3.3.2. Main compressor component

3.3.2.1. Air inlet filter

3.3.2.2. Air intake valve

3.3.2.3. Compressor element

The compressor element is optimised to bring performance especially on higher pressures.

3.3.2.4. Non return valve