FAQs on Air Compressor Maintenance & More

Firstly, oil purification is an advanced Proactive Maintenance technique for maintaining the life of a compressor. It is designed to address the root causes of oil degradation and most routine air compressor maintenance. Oil purification is proven to extend the service life and change intervals of compressor oils and other critical components.

It works by removing the harmful contaminants that accelerate oil degradation, produce acids, and promote corrosion, wear and fouling. Oil purification has been used extensively in expensive turbine oil systems and other large industrial fluid applications. Now, this same proven technology is available on a smaller scale to purify oil-flooded rotary screw compressor fluids.

Simply put, oil purification is a better, less expensive, less time consuming way to maintain rotary screw compressors. Purification of rotary screw compressor oils essentially maintains the compressor from the inside out. It does so by continuously reducing the harmful acidic and ultra-fine solid contaminants. These are the root cause of most compressor maintenance and repairs. Oil purification is proven to increase the service life. Additionally, it extends the change intervals of compressor fluids, separators, bearings, valves, seals and other vital components.

Oil purification reduces operation and maintenance costs by increasing the service life of these components. It results in reduced fluid, separator and parts purchases, lower separator energy consumption, reduced compressor maintenance and repair labor. Finally, it helps by the environment in reduced oil disposal and less equipment downtime.

The Fluid Metrics COP combines Ion Exchange technology with ultra-fine particle filtration to continuously remove chemically reactive and catalytic contaminants. They are known to accelerate oil degradation and promote wear, corrosion, and fouling.

The Fluid Metrics COP is installed in a bypass loop in the compressor’s main oil circuit. It continuously purifies a very small slip-stream of oil and does not replace or interfere with the compressor’s main oil filter. Portable filter carts only provide temporary mechanical filtration. However, the Fluid Metrics COP helps maintain the oil in like-new condition by providing continuous mechanical and chemical filtration.

Ion Exchange technology relies on the electrical attraction of oppositely charged matter (ions) to selectively adsorb and neutralize materials. An Ion is an atom, or group of atoms, that has an electrically positive (cationic) or negative (anionic) charge. When compressor fluids degrade, they produce acidic compounds comprised of cationic Hydronium ions. The Fluid Metrics COP utilizes a specially formulated anionic media whose negative charge attracts the positively charged acid molecules.

When oil containing acids comes in contact with Fluid Metrics’ ion exchange media, the acid molecules are adsorbed by the media and removed from the oil. These harmful acid molecules are permanently bonded to the media. They then neutralize the oil and controls Total Acid Number or TAN. This is a one-way reaction where nothing is released back into the oil, unlike other ion exchange processes. As a result, that would cause sludge or otherwise change or harm the oil.

Ion exchange technology was first used commercially in water purifying applications back in the year 1915. Early ion exchange media were naturally occurring zeolite soils which were effective but had low adsorption capacity and selectivity. They often leached unwanted material back into the fluid. These short-comings led to the development of synthetic ion exchange media. They are designed to have much greater adsorption capacity and selectivity while not adding any contaminants to the process fluid. Synthetic Ion exchange media are used extensively today's industries. These include the chemical, industrial, petrochemical, pharmaceutical, food processing, nuclear, mining and water treatment applications.

Fluid Metrics utilizes a proprietary high capacity anionic exchange media that is specially processed for this application. Fluid Metrics’ ion exchange media complies with Food Grade regulations and conforms to FDA regulation 21 CFR 173.25. The ion exchange technology used has been extensively tested by The Dow Chemical Company, the world’s leading maker of synthetic rotary screw compressor lubricants. Nearly three years of testing by Dow Chemical proved conclusively that the ion exchange technology used in Fluid Metrics COP is “extremely effective at removing acids and controlling TAN and pH” in synthetic compressor fluids; and, that this technology “did not contaminate or otherwise harm the treated lubricants in any way.”

In short: no. Standard OEM oil filters are designed only to remove coarse solids. They do nothing to remove the ultra-fine, clearance-size solids or the harmful acids found in all compressor fluids. These “solids-only” filters typically have a 10 micron nominal rating (25 microns absolute). They provide only the bare minimum level of protection for compressor bearings, shaft seals and air-ends. Standard oil filters are full flow filters that are designed for relatively high flow rates. As a result, they have to balance filtration efficiency (micron rating) with pressure drop. Harmful ultra-fine solids and highly reactive acid contaminants are allowed to accumulate in the oil. They accelerate oil degradation, wear, corrosion, and fouling. Standard filters ignore the root causes of compressor fluid and separator replacement. Unfortunately, these filters guarantee a never-ending and expensive cycle of unnecessary fluid, separator, and parts consumption.

Under normal compressor operating environments, purifying the oil with the Fluid Metrics Compressor Oil Purifier (COP) will extend fluid service life 3-5 times the oil’s rated service life. Actual fluid life will vary depending on several factors. These included lubricant type, degree and type of contaminant loading, and compressor fluid operating temperature.

No. The COP’s ion exchange technology is designed to selectively remove only the harmful acidic contaminants and will not affect the oil’s additives or introduce any harmful constituents into the oil. Extensive testing performed by Dow Chemical, the world’s leading supplier of synthetic compressor fluids, determined that this technology “did not contaminate or otherwise harm the treated lubricants in any way.”

The Fluid Metrics COP is effective at extending fluid life and change interval of most of today’s synthetic and hydro-treated compressor fluids. These include Polyglycol / POE, PAO, Food Grade PAO’s, and Esters based fluids. Some of the more common OEM brand names that fall in this category are:

• Sullube®.
• SRF®.
• Ultra Coolant®.
• AEON 9000®.
• QuinSyn Plus®.
• HD Roto Fluid®.

Yes. The COP can be installed on any compressor. Our COP installs in an auxiliary bypass loop to the compressor’s standard oil filter and purifies only a small slip stream of the compressor’s main oil flow. The COP uses existing oil pressure to circulate the oil and needs less than 20 psig of differential pressure.

The COP includes an installation kit which includes practically everything needed to install the COP on your compressor. Since the designs of compressor oil circuits differ among manufacturers, installation requirements will vary. Consult Fluid Metrics for installation details.

Oil separator life is generally determined by one thing. The pressure drop caused by fouling of the separator element(s) from ultra-fine solid contaminants. The Fluid Metrics COP reduces the number of ultra-fine solids that foul oil separators and increases pressure drop. We conducted field tests on highly contaminated compressor fluids. The COP reduced ultra-fine solid levels lower than brand new oil. It also drastically slowed the increase in separator pressure drop. Reducing these solids keeps the separator elements cleaner; extends their service life; and lowers the compressor’s energy consumption.

Oil separator life is generally determined by the pressure drop caused by fouling of the separator element(s) from ultra-fine solid contaminants. The Fluid Metrics COP reduces the number of ultra-fine solids that foul oil separators and increases pressure drop. We conducted field tests on highly contaminated compressor fluids. The COP reduced ultra-fine solid levels lower than brand new oil. It also drastically slowed the increase in separator pressure drop. Reducing these solids keeps the separator elements cleaner; extends their service life; and lowers the compressor’s energy consumption.

Oil degradation is a series of harmful chemical reactions that occur between the oil’s base stock, its additives, and foreign contaminants like oxygen (air), water (humidity), metal particles (rust & wear), chemical vapors, and many others. These reactions change the oil’s chemical and physical properties which negatively impact the oil’s performance ability and reduce its useful service life.

Oxidation, the chemical reaction of an oil molecule with oxygen, is the most common and most harmful of these reactions resulting in permanent chemical changes to the oil’s base molecules. Once initiated, this auto-catalytic reaction is self-sustaining and continuously accelerates producing acids and other reactive byproducts. Compressor oil oxidation may be seen from increasing acid levels or TAN. It may also be seen in decreasing pH, increasing viscosity, rust in filters, and varnish or sludge formation. Degraded oil that is left in the compressor too long may cause serious and catastrophic failure to rotary screw compressors.

In a word – Contamination. Contamination is the root cause of oil breakdown or degradation. Absent any contamination, most synthetic oils could last indefinitely.

Contamination is any foreign matter or energy that comes in contact with the oil. The most common contaminants include oxygen, acids, water, dirt, rust, wear metals, chemical vapors, pollution, and heat. Contaminant sources may be external in rotary screw compressors and ingested from the surrounding air. They can also be internal from the byproducts of chemical reactions, condensation, wear, and corrosion.

Avoid common external contaminants such as acid gases like those found in diesel exhaust, boiler exhaust, and cooling tower exhaust. Eliminate external contaminants by installing a remote air inlet to obtain cleaner, drier, cooler air from a different source. Contaminants ingested by the compressor may be controlled through continuous oil purification.

The Fluid Metrics COP minimizes separator fouling and pressure drop. Compressor energy consumption (horsepower and kilowatts) is a function of three things. 1. Compressor and motor efficiency. 2. Flow rate (cfm). 3. Discharge pressure (psig). As a general rule, compressor horsepower increases 5 % for every 10 psig increase in compressor discharge pressure. This is equal to ½ % power per psig. The oil separators in rotary screw compressors create a pressure drop that can vary from 2 – 15 psig depending on separator design and the degree of fouling of the separator element(s).

This pressure drop causes the compressor to work harder to maintain system air pressure. As a result, it wastes significant money in unnecessary energy costs. Separator elements fouling is caused by the ultra-fine solid contaminants. They are carried by tiny oil aerosols and impinge on the surface of the separator. Fluid Metrics COP removes the ultra-fine solids too small to be trapped by conventional filters. Additionally, it minimizes fouling and pressure drop of separator elements.

Not completely. However, the speed at which these oils degrade can be dramatically slowed by addressing the root cause of oil degradation – Contamination. Oil degradation rates are drastically affected by temperature and contamination. By design, rotary screw compressors continuously pump oxygen, water vapor, and other reactive and catalytic contaminants into the oil while adding heat which elevates the oil’s temperature. Minimizing the oil’s operating temperature and its level of reactive contaminants will significantly slow the rate of oil degradation and dramatically extend its useful service life and change interval.

Rotary screw compressors are one of the most severe applications possible for an industrial lubricant! Unlike other types of rotating equipment, oil-flooded air compressors have a Forced Contamination design. They are inherently open to the atmosphere continuously ingesting airborne solid and vapor contaminants forcing them into the oil.

Oil flooded rotary screw air compressors are very effective scrubbers of the atmosphere. They stripp solid and vapor contaminants from the ingested air and deposit them into the oil. Even barely detectable levels of airborne contaminants may be absorbed by the oil where they accumulate and can concentrate to destructive levels. Air compressor maintenance workers may be unaware they may have a problem with airborne contaminants. That is, until a catastrophic failure occurs and post-failure oil analysis reveals the nature of contamination.

Combining this continuous, forced-contamination design with heat, severe aeration and agitation, requires air compressor fluids to perform in one of the most aggressive environments possible.

Oil that has degraded past the manufacturer’s recommended limits can cause catastrophic failures to rotary screw compressors. As oil degrades, its ability to lubricate, cool, resist foaming, and inhibit corrosion deteriorates and negatively impacts the performance and service life of every component that comes in contact with the oil. Depending on the type of oil, sludge and varnish can also form resulting in expensive failures to bearings and air-ends and extended compressor down-time.

Effective contamination control is a three step process that begins with prevention. Providing the cleanest, driest and coolest inlet air supply and maintaining the inlet air filters will reduce the external ingested contaminant loading to the compressor fluid. Next, practicing proactive oil maintenance using the Fluid Metrics COP to continuously remove the acidic and ultra-fine solid contaminants will preserve the oil’s original physical and chemical properties. Lastly, maintaining compressor fluid levels by regularly adding make-up oil helps replenish oil additives and prevent the natural concentration of contaminants caused when fluid volumes decline from oil carryover and leaks.

Oil analysis is the only reliable way to know when it’s time to change the oil. Oil suppliers routinely provide general oil change guidelines like “every 8,000 hours, or once a year, or as determined by fluid analysis . . . whichever occurs first”. Time based guidelines are never accurate as they ignore the compressor’s actual operating conditions and environment.

Some OEM “8,000 hour rated fluids” have been known to only last 2,000 hours in harsh environments while others have tested satisfactory up to 10,000 hours in mild environments. Without performing periodic fluid analysis, users are only guessing about the condition of their fluid and run the risk of either doing harm to their compressor by running their oil past its useful life or wasting money by changing their oil too soon. Oil analysis is an easy, inexpensive way to accurately determine fluid change intervals and to alert compressor users to impending problems. We recommend users consult their fluid suppliers to obtain their specific condemning values of the key chemical and physical parameters monitored by routine oil analysis.

Finally, as a general rule, an effective oil analysis program should focus on leading indicators that anticipate and help prevent compressor problems rather than trailing indicators that only serve to alert the user to an existing problem. These leading indicators will vary depending on lubricant type but several parameters are universally important.

They include TAN (Total Acid Number), pH, viscosity, and contamination. Since many of today’s new compressors are filled with Polyglycol based lubricants, the following comments are specific to Polyglycol based synthetic fluids and are intended to provide general guidance as to your oil’s condition.

Consult your lubricant supplier for specific recommendations on testing and change-points for your specific fluid. TAN – Total Acid Number is a measure of the oil’s acid level and is widely used to determine the remaining useful life of the fluid. New fluids will have a TAN value of less than 0.10 and this value will increase as the fluid oxidizes and as a result of acid gas ingestion. The normal recommended change point in air compressor maintenance for TAN is 1.0. During normal fluid oxidation, TAN values will increase gradually at a steady rate to a value of 1.0. Above 1.0, TAN values will increases exponentially and can run-away in a relatively short period of time.

Air Compressor Maintenance & TAN

If TAN value is allowed to increase to 2.0, it is generally recommended that the oil be drained and the compressor flushed prior to refilling. pH – pH is also a measure of the oil’s acid level with new oils having a pH value around 8.0 which gradually decreases towards a value of 5.0 as the oil oxidizes. Be on the look out for a rapid or excessive drop in pH, while TAN values are otherwise normal. This indicates that external acidic gases or other oxidizing agents are being ingested from the atmosphere.

When the oil’s pH value drops below a value of 4.5, the fluid should be changed to prevent corrosion. Viscosity – Viscosity is a measure of the resistance of a fluid to flow. As oil degrades, its molecules polymerize into larger molecules increasing the oil’s viscosity. It is normal for viscosity to increase within 10% of the new oil viscosity. An increase greater than 10% or a decrease in fluid viscosity is usually an indication of contamination or varnish or sludge formation with non-polyglycol based fluids.

It is rare to change compressor fluids solely based on viscosity without other abnormal indications.