Preventing fluid contamination

Implementing proper methods of filtration is the most effective way to eliminate contamination in hydraulic systems

By Steve Krasicky, Program Manager for Industrial Products, Purolator Facet Inc.

PlantServices.com

Contamination of hydraulic and lubricating fluids, as well as lack of adequate filtration, is a leading cause of hydraulic system and component failure. To successfully maintain hydraulic systems and components, one must understand the specifics of fluid contamination, the sources for system contamination, and why filtration is the most cost-effective way to maintain fluid cleanliness.

Fluid contamination is a major contributor in approximately 70% of hydraulic system failures. Contaminant particles find their way into pumps, valves, servo-valves and various hydraulic system components where they cause wear. In extreme cases, they can cause a component to seize. Annual expense for hydraulic system maintenance totals hundreds of millions of dollars in the United States alone.

By eliminating the particles and fibers that cause wear in these systems, many of these expenses can be avoided. What is the simplest means of eliminating these dreaded particles? Filtration.

Hydraulic systems rely on a clean, properly specified fluid to deliver consistent power. Every hydraulic system requires some degree of filtration to keep the fluid clean. Removing particles that harm the system, or more specifically, system components, will prevent premature wear and prolong the system’s life. By implementing proper filtration and systematic maintenance, plant managers can eliminate 80% of the potential causes of premature hydraulic system failure.

Harmful contaminant particles come in a variety of materials, shapes and sizes. Some of the most harmful are invisible to the naked eye. A good guideline: Any particle smaller than 40 microns in diameter is invisible to the naked eye. When suspended in liquids (such as hydraulic oil), the limit of human visibility decreases to 70 microns. Even if a fluid sample “looks clean,” it could be loaded with particles in the critical damage range.

Ironically, the common process of taking an oil sample by dipping a transparent container in the fluid reservoir may actually introduce contaminants into the system. This procedure allows airborne contaminants (and contaminants adhering to the bottle) to enter the reservoir. This critical range is usually in the 3-to 8-micron-diameter size, and particles within this range account for the majority of wear within hydraulic systems. This range represents the clearance size for many critical components, including servo-valves and piston pumps.

Types of contamination

There are many ways a system can become contaminated with the four primary types: built-in contamination, fluid contamination, environmental contamination, and self-generated or system-wear contamination.

Built-in contamination has its source at the point of system or component manufacture. It can come from the residue of manufacturing, assembly, testing and packaging of hydraulic components. These contaminants include core sand, weld spatter, metal chips, lint and abrasive dust. One can prevent early system failure by removing these contaminants with a very fine filter at startup.

Employing proper component selection, manufacturing methods and component cleaning practices can eliminate most built-in contamination. However, avoid homemade reservoirs because of the high incidence of weld splatter inherent in these units.

Fluid contamination, surprisingly, exists in hydraulic oils and lubes when they are purchased. Typically, they are much dirtier than industry standards recommend. New hydraulic and lubricating fluids should be filtered before use, regardless of how or when the fluid will be used, whether at system startup or for simply topping off the reservoir.

Most suppliers offer new hydraulic and lubricating oils that are certified to a specific ISO cleanliness code. The most widely used method or standard for representing fluid cleanliness is the ISO Solid Contamination Level Code (ISO 4406). One must also make sure the fluid meets Cleanliness Codes per ANSI/(NFPA/JIC) T2.24.1-1991 (see Table 3). Filtering oil before using it is the most cost-effective way to ensure that only clean fluid enters the reservoir.

Environmental contamination comes from the conditions that surround the component or hydraulic system. Airborne contaminants are most likely particles measuring less than 30 µm in diameter. Moisture can enter the system as free water or as condensate from humid air. This type of contamination can enter through reservoir ports and tops that are left open or components exposed during maintenance. In addition, dirt can bypass faulty rod seals. The most effective way to exclude this contaminant type is to make sure system reservoirs are completely sealed, that rod seals are effective, and that some type of filtration system is in place. The system must remove the contaminant before it enters the fluid. Breathers, for example, can absorb moisture and filter solid particles.

Self-generated contamination (particles comprised of wear debris) is generated during system operation. These contaminants must be removed while the component or system is in operation. Pump vanes, rod ends and hoses generate small particles that must be filtered out to prevent debris from causing system wear. Removing contaminant particles as they are generated minimizes this normal “wear and tear.”

Target Levels of Cleanliness