Myths and Facts About Compressed Air
Important notes on air treatment
for textile plants.
by Imtiaz Rastgar.
Myth: It is safe
to clean dirt and debris from a work area using compressed air.
Fact: No. This is an unsafe practice.
Cleaning a work area using compressed air could result in
serious injury as a result of particulate striking or entering
the eyes, ears or skin. A safer alternative is to use a vacuum,
mop or broom to remove dirt and debris.
speed drive is always the best solution for the most efficient
Fact: Not necessarily. Inherent to their
design, variable speed drive compressors have an optimum tip
speed range where they operate most efficiently. If the
compressor load requirements fall outside of this range, other
control options may provide the most efficient solution. The
compressor provider will need to consider the numerous
application requirements in order to recommend the most
efficient compressed air solution for the job.
speed drive increases oil carryover.
Fact: Operating at reduced speeds should
have no detrimental impact on oil carryover. The reduced airflow
will lower the velocity through the separator media, which will
improve its efficiency. There are two primary contributors to an
increase in carryover, lower pressure and higher temperature.
Neither of these issues is caused by the addition of a VSD.
variable speed drive compressor eliminates the need for a flow
Fact: every application is different, but
there are clearly systems that would benefit from the stable,
constant pressure that a flow controller can provide in a very
dynamic system and the part load efficiency of a VSD compressor.
Even with a flow controller and proper storage, an optimized
system will fill the storage in the most efficient manner. In
many systems, this can include a VSD compressor.
“Synthetic” compressor fluids are the same.
Fact: No, they are not the same. When
looking at air compressor fluids, the term “Synthetic” is often
used to describe the base stock. Since “Synthetic” simply means
that the fluid is not a hydrocarbon base stock, it encompasses
many different base stocks which offer dramatically different
performance. The real question is what is the synthetic base
stock, PAG, Diester, PAO? Once you determine the base stock you
can evaluate its advantages and disadvantages.
Polyglycol(PAG) blended compressor fluids are the same.
Fact: Polyglycol compressor fluids are
generally blended with one of two types of ‘Esters,’
“Polyolesters” or “Diesters.” These two differ drastically in
their performance in a rotary screw air compressor.
Polyolesters (POE): POE's handle heat very
well and run varnish and sludge free. They are best known as jet
engine lubricants. They are expensive and are used in
applications where performance is critical, like in a rotary
screw air compressor.
Diesters: Diesters are low cost and have
the potential to cause sludge. Sludge can become very costly to
a company's bottom line, reducing compressor efficiency and
becoming very expensive to remove from a compressor system once
it forms. Diesters also cause swelling in gaskets, seals, and
hose liners. This results in problems with leaks, swelling of
O-rings and deterioration of shaft seals.
BEWARE, many generic Polyglycol/Ester
blends turn out to be a Diester base with a minimum amount of
Polyglycol. These generic fluids will have all the issues
associated with a Diester fluid.
replacement parts and compressor lubricants are the same as
manufacturer proprietary parts and lubricants.
Fact: Maintenance kits and manufacturer
proprietary replacement parts and lubricants offer the best
overall performance. They are designed to maintain unit
efficiency and reliability. Generic parts increase liability,
decrease performance, and may void manufacturer warranties.
elements should only be changed when the differential pressure
Fact: you install compressed air filtration
to improve air quality. DP gauges/indicators are blockage
indicators not air quality indicators. To ensure your compressed
air quality, filter elements should be changed annually in line
with manufacturer's instructions.
filters are ONLY for oil removal.
Fact: Coalescing filters have an even
higher capture rate with solid contaminants than with liquids.
contamination is not present in atmospheric air.
Fact: Atmospheric air typically contains
between 0.05mg/m3 and 0.5mg/m3 of oil vapor from sources such as
car exhausts and industrial processes. As oil-free compressors
use large quantities of atmospheric air and atmospheric air
contains oil vapor which can cool and condense in the compressed
air systems, the use of oil-free compressors does not guarantee
and oil aerosol are the only contaminants present in a
compressed air system.
Fact: Generally, there are ten contaminants
found in a typical compressed air system that need to be removed
or reduced for the system to run efficiently.
The ten contaminants are:
Rust Atmospheric Dirt.
Only two of these contaminants, liquid oil
and oil aerosol are introduced by a lubricating compressor. The
purification equipment required to reduce, or remove the
remaining contaminants by virtue of their operation also remove
liquid oil and oil aerosols. Therefore regardless of the type of
compressor installed, purification equipment is required.
air contamination is a compressor issue.
Fact: In a typical compressed air system,
compressed contamination comes from four different sources,
1. Source 1 - Atmospheric Air
Air compressors draw in huge amounts
of atmospheric air, which continuously fills the system with
contaminants such as water vapor, micro-organisms, atmospheric
dirt and oil vapor.
2. Source 2 - The Air Compressor
In addition to the contaminants
drawn in through the compressor intake, the compressor also adds
additional wear particulates from its operation. Additionally,
oil lubricated compressors carry over liquid oil, oil aerosols
and oil vapor from the compression process. Once through the
compression stage, the after-cooler will also condense water
vapor, introducing it into the compressed air in both a liquid
and aerosol form.
3. Source 3 - Compressed air
4. Source 4 - Compressed air
The air receiver (storage device) and the
system piping that distributes the compressed air around the
facility both store large amounts of contamination.
Additionally, they cool the warm, saturated compressed air which
causes condensation on a large scale, adding liquid water into
the system. This saturated air and liquid water leads to
corrosion, pipe scale and microbiological growth.
Myth: Static Oil
Water Separators are not suitable for synthetic lubricants /
PAG's. This is evident with cloudy outlet water.
Fact: Oil Water Separators are designed to
reduce oil in water levels to acceptable limits. Some lubricants
such as synthetics / PAG's also contain detergents and additives
to extend the life of the compressor. Oil water separators are
not designed to remove detergents and additives. Oil in water
content cannot be accurately determined from visual inspection
and lab analysis should be used. Lab analysis on cloudy outlet
water is the only way of accurately testing oil in water content
and will show it is within acceptable limits.
Myth: Any dryer
(refrigerated or desiccant) can be installed outdoors.
Fact: All standard dryers are designed for
internal installation. However, many are often installed
outside, (with a lean-to roof in some cases and without a
lean-to roof in some cases). Outside installation is acceptable
provided there is lean-to roof with freeze / snow protection,
blowing rain protection, and a roof / ceiling high enough to
avoid hot air re-circulation. Outside installation of standard
dryers with no roof is not recommended.
In the case where outside installation
without roof is a necessity, request an outdoor modification
package including freeze protection, UV protection in paint,
fasteners and electronics, and Nema 4 components throughout. A
Nema 4 electrical enclosure alone is not sufficient for an
outdoor without roof installation.
Myth: Most dryers
do not provide dryness levels to the same levels quoted in sales
Fact: Dryer installations are often
plagued with a variety of mistakes which impact the level of
compressed air dryness which they provide. Classic installation
mistakes are: insufficient space above or in front of condenser
air discharge which causes recirculation and high pressure
faults…dramatic under sizing of the dryers when forgetting that
cooling water and ambient air in summer is at far higher
temperatures than in winter…wrong power supplies are amazingly
frequent. Often dryers are on the same power line as other
capital equipment and so the actual voltage is subject to
tremendous dips which play havoc with dryer operation and
air filters also dry compressed air.
Fact: Compressed air filters are capable
of removing bulk liquid water and some water aerosol from
compressed air. Compressed air filters are not capable of
reducing the level of moisture vapor in compressed air or
reducing the pressure dew point of compressed air.
further clarification contact Sakoon