The precise design of fluid-using systems in today’s machines—whether fuel, hydraulic, transmission, or engine—demands a higher level of fluid cleanliness than ever before. To that end, equipment manufacturers have developed highly efficient filtration systems, but given the extreme intolerance to even minute particulate contamination exhibited by these systems, more equipment owners are considering supplemental filtration as a means of boosting protection for extended component life.
For example, common-rail fuel-injection systems, which greatly increase combustion efficiency, routinely operate at pressures of 30,000 psi or more. Maintaining these pressures requires that fuel-delivery components have extremely tight machining tolerances, some no more than two microns—a dimension that one filter manufacturer equates to the thickness of a single bacteria cell. (About 35 of these cells placed side-by-side would be required to equal the diameter of a human hair.)
Likewise, hydraulic systems in today’s machines—whether powering implements, driving hydrostatic propulsion systems, activating clutches and brakes, or providing exacting control of these functions—are being more precisely engineered as they compete for space within the machine’s design envelope, sometimes vying for real estate with bulky exhaust after-treatment hardware.
To help equipment manufacturers make the best use of space without compromising performance, hydraulic suppliers are developing more-compact components, which generally operate at substantially higher pressures. (Theoretically, for example, the size of pumps and motors can be halved if pressure is doubled.) These components are robustly built to sustain increased loads, but they also have much tighter machining tolerances to maintain long-term efficiency. As with high-pressure fuel systems, efficient hydraulic filtration is all the more critical today.
“Most damage to hydraulic systems is done by particulates smaller than 7 microns and by water,” says Keith Nye, owner of Perfect Filtration Systems.
Pierre Nieuwland, president and CEO of NTZ Micro Filtration, makes the further point that control valves in today’s machines are especially vulnerable to particulate contamination:
“With new technologies in hydraulics and transmissions, the sensitivity of components, in terms of cleanliness, is becoming more critical every day,” says Nieuwland. “Electro-hydraulic valves in these systems are particularly sensitive, and the demand for cleanliness is becoming more of an issue.”
And diesel-engine oil, too, bears the burden of today’s technology. Engine oil must circulate through a power plant that is running generally hotter than before, in part the result of its obligation to meet emissions standards, and often must handle an added particulate load imposed by an exhaust-gas-recirculation (EGR) system, which retards formation of toxic nitrogen oxides.
“The use of EGR introduces soot and combustion by-products into the aspiration gas,” says NTZ’s Nieuwland, “increasing the oil’s stress index and adding to the quantity of soot in the engine.”
Both NTZ’s Nieuwland and Perfect Filtration’s Nye say that as more machine owners recognize the critical need for fluid-system cleanliness, supplemental filtration is getting a second look.
On the fuel side, says Nye, equipment owners are becoming particularly cognizant of the need to use high-efficiency filtration at the point of dispensing fuel. But in locations where such systems are not being used, he says, supplemental filters are now more often being added to the machine. For oil-using systems, he says, high-efficiency by-pass filtration is gaining wider use as a means for adding another level of component protection.
By-pass filtration involves continually diverting a small volume of oil from a system’s main flow (usually 0.5 to 2.0 gallons per minute), passing it at reduced pressures (15 to 50 psi) through an extremely fine filter that also removes water, and then returning this “polished” oil to the system’s sump. The parallel by-pass system thus supplements the filtration capability of the machine’s factory-installed, “full-flow” filter, which must accommodate the system’s full oil flow at full system pressure.
“A by-pass system tees into a pressure source, then controls the volume and pressure of oil passing through a dense, depth-type cellulose media that absorbs water and can trap solids below 1 micron,” says Nye.
Depth-type filtration is sometimes equated—graphically, but not too accurately—as being akin to forcing fluid through a roll of bath tissue to trap contaminants within its large mass. This contrasts with “surface-type” or “membrane-type” filtration, in which a barrier, such as pleated-paper, blocks contaminants. Because the depth-type filter has a large surface area to trap contaminants, says Nye, its effectiveness is enhanced.
Proponents of by-pass systems reason that, because the full-flow filter must continuously handle a system’s complete circulating oil volume and yet be of a practical size so as to fit within the machine’s space constraints, filtration effectiveness must be balanced with an acceptable flow rate and an acceptable pressure drop across the filter. By contrast, since pressure and volume are limited in a by-pass system, the degree of filtration need not be.
“We see the primary use of by-pass filtration for hydraulic systems and transmissions, because cleanliness of the fluid in these systems is paramount,” says Nieuwland. “Installation of by-pass filtration on engines usually comes later—when the user has experienced the effects and benefits of the process in other systems.”
Although by-pass filtration will extend oil-drain intervals, says Nieuwland, “the motivation for installing these systems should be to extend component life by means of reduced wear. Statistics from component suppliers clearly show that by lowering contamination levels, component life rises—sometimes as much as eight times longer than the predicted average.”
By-pass filtration advocates also say that the system’s ability to trap a higher percentage of very small particulates and to absorb water retards a number of harmful effects, including the breakdown of base oil, additive depletion, viscosity increase (because of particulate load), and the formation of sludge, sediment, varnish, and acid. Extending additive life is claimed to help the oil do its job better, longer, thus offering the prospect of significantly increased drain intervals.
Nieuwland cites another potential benefit for using by-pass filtration for engines. He relates an incident in which a cylinder-liner seal failed in a customer’s over-the-road truck, but by-pass filtration so effectivcely absorbed the antifreeze leaking into the oil, that the engine was unharmed, as revealed by a subsequent teardown.
Nieuwland does caution, however, that adding by-pass filtration to an old engine may cause it to leak, because detergent and dispersant additives in the oil now have a better chance of cleaning deposits, which might have been keeping hardened seals functioning. But in time, he says, seals will likely regain perhaps 80 percent of their flexibility, and the leaking will stop.
By the time diesel fuel travels via pipeline from the refinery to the terminal, is transferred to the oil distributor’s trucks, delivered to a machine owner’s bulk-storage tank (where it might be especially vulnerable to fouling by water-induced debris), it can potentially pick up significant contamination.
Fuel being dispensed from a typical bulk tank, according to some industry statistics, might have an ISO (International Standards Organization) cleanliness rating of 22/20/18. As measured by ISO 4406, this rating means that present in one milliliter of fuel (less than a half fluid ounce) are 20,000 to 40,000 particles 4 microns and larger, 5,000 to 20,000 particles 6 microns and larger, and 1,300 to 2,500 particles 14 microns and larger. This rating makes the fuel unsuitable for use in a high-pressure common-rail fuel system.
Target cleanliness for fuel after passing through the machine’s on-board filtration system, say the same statistics, should be on the order of ISO 15/13/10, which reduces particles 4 microns and larger to no more than 320, 6 microns and larger to no more than 80, and 14 microns and larger to no more than 10. Although some engine manufacturers would like to see even cleaner fuel for Tier 4-Final engines, most agree that these numbers are likely the practical limits for in-field cleanliness.
The point is, say the experts, that exponential reductions in fuel contamination can be achieved by practicing proper storage and filtration techniques, which might include filtering fuel entering bulk storage, filtering it when dispensing, using effective tank breathers (to reduce the prospect of drawing in contaminants and moisture as the tank breathes), and installing supplemental on-board filtration to complement these efforts—or to compensate for their lack.
“The first step in protecting equipment is to dispense fuel that has been filtered equal to—or better than—what the vehicle’s filters will do,” says Howard Chesneau, president of Fuel Quality Services, a company that assists clients with fuel-related machine-operability issues. “Filtration is critical to the operation and longevity of Tier 4 common-rail fuel systems. It’s never made sense to me that fleet owners would place loose filters on their ground systems—or worse, not filter either the intake or output of the ground system—and yet rely on the super-tight filters on rolling stock to do the job.”
As Perfect Filtration’s Nye suggests, in situations in which loosely filtered or unfiltered fuel is being dispensed into machines having exceedingly contaminant-intolerant fuel systems, supplemental filtration can be an important adjunct to the machine’s factory-installed filtration/water-separator system.