Compressed Air Explained This
section explains the basics behind compressed air.
Why Do We Need It?
Compressed Air is often
described as the fourth utility, although not as ubiquitous
as electricity, petrol and gas, it plays a fundamental part
in the modern world. The main difference is that users
generate their own air and so have a choice in the way that
air is generated.
The importance of compressed air
is often over looked, but in reality it plays a vital part
in most modern manufacturing processes and modern
civilization. Although we may not realize it most products
we use today could simply not be made without compressed
air. Compressed air accounts for about 10% of the global
energy used in industry today.
With so many applications in
different environments being dependant on compressed air,
the compressors not only have to compress the air to a
specific pressure, at a certain flow, it has to deliver air
of the right quality. To most people, a compressor is all
that is required to compress air, but to obtain the right
quality of the compressed air, more equipment is often
needed. Filters and dryers are often needed to remove oil
and water before it reaches the application. CompAir has a
range of completely oil-less compressors where air comes
into contact with the process it serves and so the quality
is critical, for example in where a compressor may be used
in a food packaging role.
The three different types of
Piston Compressor: The
piston compressor is one of the earliest compressor designs,
but it remains the most versatile and is still a very
efficient compressor. The piston compressor moves a piston
forward in a cylinder via a connecting rod and crankshaft.
If only one side of the piston is used for compression, it
is described as single acting. If both sides of the piston,
top and underside are employed, it is double acting.
The versatility of the piston
compressors knows virtually no limits. It compresses both
air and gases with very little alterations. The piston
compressor is the only design capable of compressing air and
gas to high pressures, such as breathing air applications.
The configuration of a piston
compressor can be a single cylinder for low pressure/low
volume to a multi-stage configuration cable of compressing
to very high pressure. In these compressors, air is
compressed in stages, increasing the pressure before
entering into the next stage to compress the air into even
Rotary Screw: The screw
compressor is a displacement compressor with pistons in a
screw format; this is the predominant compressor type in use
today. The screw compression element main parts comprise
male and female rotors that move towards each other while
the volume between them and the housing decreases. The
pressure ratio of a screw is dependent on the length and
profile of the screw and of the form of the discharge port.
The screw element is not
equipped with any valves and there are no mechanical forces
to create any imbalance. It can therefore work at high shaft
speed and combine a large flow rate with small exterior
Rotary Vane: Based on
traditional, tried and tested technology, the vane
compressor is directly driven at very low speed (1450rpm),
offering unrivalled reliability. The rotor, the only
continually moving part, has a number of slots machined
along its length into which fit sliding vanes that ride on a
film of oil.
The rotor rotates within a
cylindrical stator. During rotation, centrifugal force
extends the vanes from their slots, forming individual
compression cells. Rotation decreases the cell volume,
increasing the air pressure.
The heat generated by
compression is controlled by pressurized oil injection.
The high pressure air is
discharged through the outlet port with the remaining traces
of oil removed by the final oil separator.
Once air has been compressed,
why refine it?
Air is a colorless, odorless,
tasteless mixture of many gases, primarily nitrogen and
oxygen. Air is naturally contaminated with solid particles,
such as dust, sand, soot and salt crystals. This
contamination varies with differing environments and
Water vapor is another natural
ingredient which can be found in variable amounts in the
air. The amount of water vapor and contamination of the air
plays a vital role in the compression process and in the
quality of the air delivered by the compressor.
The damaging and corrosive
properties of water are well known. Untreated air at
atmospheric pressure contains large amounts of water and
other contaminants such as oil droplets and dirt particles.
When the air is compressed the
concentration of moisture and other contaminants increases.
If allowed to remain in the system this corrosive mixture
has a detrimental effect on pneumatic equipment, causing
unnecessary production downtime, product spoilage and
reduced equipment life.
Compressed air filters remove
the oil and dirt content while compressed air dryers remove
water vapor before air reaches the point of use.
Different ways of
treating/refining compressed air
Aftercoolers are a good first step in removing moisture and
air contaminates. They lower the temperature to safe, usable
levels, thus reducing the air's ability to hold water vapor,
removing 70%. However the air is still saturated. A further
drop in temperature will cause additional condensation to
occur in downstream airlines.
Refrigerant drying Refrigerant
drying cools the compressed air, whereby a large amount of
the water condenses and can be separated. The compressed air
is then heated so that condensation does not form on the
outside of the pipe work system.
The compressed air cooling takes
place, via a closed coolant system, where a refrigerant
cooling agent is employed. CompAir uses environmentally
friendly gasses for this. By cooling the compressed incoming
air with the cooled outgoing air in the heat exchanger, the
energy of the refrigerant dryer is reduced.
Desiccant drying works on the principle of absorption of
water vapor through a bed of desiccant material, in a pair
of chambers. Two types are used, heatless regenerative and
heat regenerative. The heatless type uses a percentage of
the dried air (purge), for re-generation of the desiccant
material, while the heat regenerative type uses an electric
heat disk, which reduces the amount of purge air needed for
Filters and Water Separators:
WS Water Separators have been designed for the efficient
removal of bulk liquid contamination from compressed air.
Filters are used both prior to, and after compression.
Filtering the intake air reduces the intake wear on the
compressor by removing larger particles. During the
compression air can be contaminated with oil (in oil
lubricated machines) which is removed by filters. The filter
efficiency is dependant on compressor type, age, design and
condition. Filters are often setup in multistage. Fiber
filters can only trap oil as droplets, while more efficient
active carbon can trap oil as a vapor. We can help you
select the right filters for your needs.