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What are contaminants
in a pneumatic system? Fluid power contaminants usually come in
three major forms.
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Built-in Contaminants in new
pneumatic systems build at the OEM’s facilities due to sub-
standers during installation/ build process/ and shipping to the
receiver’s facility.
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Wear particles Are usually
generated within the end-used working pneumatic system.
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Ingested That is caused during the
installation process or when equipment is being rebuilt or from
bad cylinder seals on the pneumatic actuators.
So let’s break
contaminants down a bit further. They will consist of particulate,
air, water, microbes, static electricity, corrosion, magnetism,
chemical and even thermal, which all will affect the pneumatic
system.
Many filtration
experts say that contaminants can be classified in three categories.
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Hard-dirt: This style of
contamination may be generated within, or outside the
faculties. This leads to component failure, thus causing faulty
pneumatic operation.
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Soft-dirt: This type of
contamination may be generated within the pneumatic system at
either assembly or disassembly. Example; pipe dope or tape
being misapplied well get into the pneumatic system like
component clearances or within the orifices. Results are the
same system operation failures.
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Entrained liquids; Undesirables
such as gases when mixed with moisture result as corrosion when
air pollution is present in the form of entrained liquids.
Example: coolants present in the atmosphere, this will lead to
rust formation with the pneumatic system. When this happens the
pneumatic component’s operation will make the valves shift
erratically.
Typically one must
remember that compressor oils being used are never compatible with
non-lubricated pneumatic systems / pneumatic component applications
being used today. When this occurs the incompatibility will lead to
varnishes and this will cause the components within the pneumatic
system to stick. Proper main line filtration must be used between
the powerhouse and the receiving facility.
Filtration becomes
very critical to the pneumatic applications. First one must
considerer what is filtration? Webster’s dictionary describes
filtration, as a porous substance through which a liquid or gas is
passed in order to remove constituents such as suspend matter.
Dr. E.C. Fitch
stated in his book entitled “Fluid Contamination Control” incipient
failure exists when fluid power system conditions are right for
surface interactions to occur. Once the surfaces begin to wear, lock
and seize; an impending failure situation exists which can only lead
to precipitous and catastrophic failures. The U.S. Army’s “Triage”
classification system of battle casualties, as indicated below,
applies to failure situation:
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Trivial---
incipient (about to occur)
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Treatable---
impending (is occurring)
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Terminal---
catastrophic (has occurred)
Controlling
contamination in a pneumatic system must always involve correct and
necessary planning, be well organized and of course doing the
implementation needed to resolve the following. One must have a
description and the identification of the contaminants, and how to
determine, and on going analyze of the contamination within the
pneumatic system. How can maintenance stop and achieve the
ingression and restrict its growth with in the pneumatic system?
Engineers and maintenance personnel must learn new methods to
prevent and protect the system against contamination. All of the
above can be done by closing the communication loop between OEM’s,
control suppliers and end-users. By doing this, will help lead to
more efficient pneumatic systems with less contamination. End-users
will benefit with better up times for their machinery.
Let’s look and
breakdown a few major terms related to contamination. First and
foremost, what is a micron? Micron is measured on the micrometer
scale as .0000039 of an inch. First, this does not take into
consideration what is the shape of the micro and its’ ability to
pass through a filter element. Filter manufacturer usually rate
their filter as either nominal or absolute. There has been much
debate over which rating is correct. In todays global everyone
should be taking a hard look at the ISO pneumatic filtration
specifications. |
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Typically the
pneumatic system uses some form of filtration at the regulator, some
end-users specify that they want to use a 40-micro and 5-micro
arrangement, other’s want only a 5-micro. A coalescing style filter
should be used in pneumatic system, but are application driven.
Remember, to look at the ISO standards for Air filter / coalescing
testing, ISO-8573 parts 1 and 2. You should consult with all
parties involved, by consulting with pneumatic control suppliers and
original equipment manufactures, to meet the needs of end-users.
Normally this is accomplished at simultaneous engineering, when
starting a new program. If air motors are being used, remember that
a lubricator is a must, this will allow for long life of the air
motor. Air motor system should also have reclassifiers in each
exhaust port to reduce the amount of contaminates (oils) released
into the facilities atmosphere. If system exhaust speed drops or
pneumatic system performance reduces this is usually due to clogging
of the reclassifies element.
For ease of
maintenance, you should always be looking at the delta-P or pressure
drop across the filter; this indicates when the element should be
changed. What is the meaning of pressure drop or pressure
differential; the change in pressure between two points of either
the system or a component. There are other means for checking for
dirty filters and one should always be looking at the end-users
pneumatic specification. Service life of the filter element is very
important, this is the length of time that the element, can remain
within the system before it must be changed.
One may want to
consider using and sizing the drip-leg that should be used to help
eliminate moisture and oils from the main supply header. If sized
correctly this will form a vortex that will take contaminates out of
the pneumatic system as the equipment is running. Some OEM’s argue
the point that the drip-leg is not to be considered to be filtration
and is too costly to add to their machinery. Make sure to always
check with the end-users pneumatic specification.
If your facility
still has issues or concerns with contamination you may want to
consult with a good filtration lab dealing in air filtration. This
would help with determining why what and how you may resolve these
concerns.
Filtration cost
typically off-set by the operation cost for the industrial pneumatic
system. Pneumatic system designers should be looking at the type of
filter media being used, replacement element interchangeable, and
types of housing being used.
In today’s pneumatic
systems one must take into consideration the environmental factors
relating to filtration. Where the equipment is being installed, is
going to be effected by the following; Temperature, humidity,
machinery utilization rate, maintenance practices and of course the
contaminant ingression rate with in the system.
One could write a
complete manual related to contamination and contaminants for all
fluid power systems. A suggestion engineering and maintenance
personnel may want to refer to their filter manufacturers /
component supplier, to determine, what is best way to off-set the
contamination for their pneumatic applications. You also can read
literature published by different filter manufacturers along with
articles/ papers written by different fluid power personnel, with
their input on this subject matter. A good start would be to check
with the National Fluid Power Association (NFPA) for filtration
standards and publications. One may also check with International
Standards Organization (ISO), Society of Automotive Engineers (SAE),
American National Standards Institute (ANSI), for their
publications. Good luck and happy reading on your new adventure in
the world of reducing contamination within your pneumatic systems.
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