The Importance of Filtration

The Importance of Filtration

More than 75% of all hydraulic system failures are a direct result of contamination. Yet a vast majority of these failures could be averted, prevented or eliminated with proper filtration.

What a waste. The staggering costs of losses from filtration failure include: loss of production resulting in downtime; component replacement costs; frequent fluid replacement; costly fluid disposal; increased overall maintenance costs; and increased product scrap rate.

An even bigger shame is how easily and inexpensively all of this waste and trouble could have been eliminated. All it takes is a modest investment in filtration – backed up by the knowledge and diligence to apply the available technology.

To start at the beginning, hydraulic fluid has four functions: to act as an energy transmission medium; to lubricate internal moving parts of components; to act as a heat transfer medium; and to seal clearances between moving parts.

Contamination interferes with all four functions of hydraulic fluid. Because clearances in hydraulic components may be extremely close, as small as 0.0002- 0.0005 inches (5-12 microns) or less, it is necessary to filter out the small particles that can interfere.

When abrasive particles of dirt enter the space between moving parts they score or hone the surfaces to greater clearances and coincidentally produce additional particles. Thus the process continues at an ever increasing speed as the system runs. As contamination grows from this process, common results include internal leakage (slippage). This lowers the efficiency of pumps, motors and cylinders and decreases the ability of valves to control flow and pressure accurately. In addition, parts stick because of sludge or silting. The end result is premature failure of components. This can lead to expensive replacement costs – as well as loss of production and other costs of unscheduled and unnecessary downtime.

To tell if you have a problem, collect oil samples from your hydraulic systems. Then, have those samples analyzed for contamination according to ISO 4406:1999 standards. They should also be analyzed for water content, oxidation, viscosity, acidity and additive depletion.

ISO 4406:1999 measures for contaminants at three size levels: 4um, greater than 6um, and greater than 14um per cubic centimeter. Report numbers on oil analysis show three levels. (E.g. 22/21/18)

As the report numbers decline, the amount of contaminant declines. The scale is easy to understand – 24 rating equals 80,000 to 160,000 parts per cc; 23 rating equals 40,000 to 80,000 parts per cc. With each step down, the level of contamination is cut in half. So, by the time we reach a rating of 16, the level is 320 to 640 parts per cc.

It really makes a difference. When we compare contamination, we see how the higher the rating, the more junk, dirt and undesirable stuff gets passed through a system on an annual basis. For example, at ISO 22/21/18, a 66 gallon per minute hydraulic pump will have four tons of dirt pass through it in a single year. Not surprisingly, the expected life of that pump is only two years.

With filtration in place to bring the rating down to ISO 16/14/11, there will only be 55 pounds of dirt passing through it in a single year. The result is a more acceptable expected life of seven years.

Sadly, even new hydraulic fluid is no guarantee of freedom from contamination. Analysis of brand new fluid, prior to filtration, will usually average on an ISO 22/20/18 rating. It needs to be filtered before it can be used with confidence.

Critical specifications of a filter are described as micron size and efficiency. Each filter will have a Beta ratio. It is important to pay attention not just to the filtration size (micron) but to the efficiency as well. For example: looks can be deceiving. A filter labeled B3=>2 is a 3 Micron filter that removes 50% of particles 3 Micron or larger. However, a filter labeled B3=>200 is a 3 Micron filter removes 99.5% of particles 3 Micron or larger. What a difference in equipment protection.


Another important variable in filtration is the element. These come in three fundamental forms: mesh, paper or spun glass fiber.

One form of mesh is stainless steel, “G.” It provides surface filtration and is partly cleanable. It works in larger sizes such as 25, 40 and 80 micron.

Paper Matting or “P.” Paper matting provides deep filtration and has high material stability and strength. Paper matting is available in 10 and 25 micron.

Interpor Fleece “VG” Glass Fiber is another option. It performs deep filtration and has high particle holding capacity. The fineness levels include 4, 5, 7, 10, 15 and 20 micron levels.
Final variables are functional.

Suction Filters are located on the suction side of the pump. These strainers protect the pump from drawing in large particles and non-system contamination. Suction strainers are often referred to by “mesh” size: 60 mesh = 238 micron; 100 mesh = 149 micron; and 200 mesh = 74 micron.

Pressure Filters are located downstream from the system pump. They are designed to handle system pressure and flow. Pressure filters protect sensitive components from pump generated contamination. Often B6=>200 is used in this application.

Return Line Filters are the last component through which fluid passes before entering the reservoir. It captures wear debris from system working components and particles entering through worn cylinder rod seals. Return line pressure is relatively low and filtration levels of B3=>200 are recommended.

Off Line Filtration consists of a pump, filter, electrical or air motor and the appropriate hardware connections. Fluid is pumped out of the reservoir, through the filter, and back to the reservoir in a continuous fashion. This method can be B3=>200 for solid contaminants. Off-Line also provides an excellent method for water removal with “Watersorp” elements.

Reduce contamination through filtration and you have gone a long way towards increasing the effective life of hydraulic components.

For more information about filtration, other problems with hydraulic systems, or a full range of fluid power systems and components, contact IBT Fluid Power Group.

Source material for this article included:
“Maintaining Hydraulic Fluids” by M. Radhakrishnan
“Hot Hydraulic Systems Need to Just Chill Out” by Alan L. Hitchcox
“8 Things Your Father Never Told You About Contamination” by Philip Johnson
“How Clean Does Your System Need to Be?” by Jeffery B. Mordas
“Have You Changed Your Oil. Program?” by Kevin Campbell
“Filtration Fact” by Parker Corp.
“Hydraulic Filtration” by Penton Publishing, Fluid Power Handbook
“Element Material” by Internormen Inc.


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