Maintenance: Filter Check, Part 1

In the dusty, dirty world you work in, heavy equipment has always been protected by a gauntlet of specialized filters. But over the past five years, changes to engine designs and new oil and fuel formulas have altered the type and the amount of contamination handled by these filters. Equipment and filter manufacturers responded with better filter technology. Knowing more about this technology will make you a better equipment manager and help you avoid unpleasant surprises in the field or the shop.

Here’s a look at the three types of filters – lube, fuel and exhaust – most affected by these changes. Next month we’ll talk about filtering hydraulic fluids, intake air, cabin air, coolants and transmissions.

  1. FUEL
    To get the reduced exhaust emissions required by the Environmental Protection Agency today, heavy diesel engines have to completely burn almost every molecule of fuel sprayed into the combustion chamber. To do this, they shoot up to three or four separate bursts of fuel into the cylinder for each single combustion cycle. The fuel injectors measure and inject the fuel in ultra-precise amounts, and in many engines that fuel blasts out of the injectors at up to 30,000 psi.

    Contamination in your fuel – particles as small as five microns – can compromise the tight tolerances injectors need to perform at this high level. And even miniscule amounts of emulsified water rob the fuel of its lubricity causing an increase in metal-to-metal wear. Clean, high performance engines won’t burn clean or fuel efficient for long without good fuel and the right filters.

    “There is now a zero or almost zero tolerance for water in the fuel,” says Dave Brisk, director of fuel product management for Cummins Filtration. “It wreaks havoc with the injectors and forces you to have good fuel water separators.”

    Biodiesel no fad
    Along with the changes in engine design, changes in diesel fuel formulas – specifically ultra low sulfur diesel (ULSD) and bio-diesel – have further complicated the issue. Biodiesel is a blend of conventional diesel fuel and plant oils that come in formulations ranging from two percent plant based (B2) to 20 percent (B20). Only a handful of cities and state agencies mandate the use of biodiesel, but its market share is expected to grow for years.

    The cloud point of B20 is typically seven degrees higher than No. 2 diesel. Microorganisms such as algae and mold grow more easily in biodiesel, creating an acidic environment corrosive to metal. Its plant based ingredients also make your fuel less heat stable, encouraging the formation of asphaltenes and other sticky contaminants that can clog a filter.

    Despite these issues, biodiesel isn’t just a fad and most of the major equipment manufacturers have approved its use. But to err on the side of caution some fuel filter manufacturers are using less cellulose and more synthetic filter media, increasing the surface area of the filter media and using more depth filters with different layers to trap different size particles. Dual filters, fuel processors and more aggressive fuel-water separation might be warranted in some cases, Brisk says.

    Say goodbye to sulfur
    ULSD fuel (15 parts per million sulfur) is mandated for all on-highway applications today and will replace the low sulfur diesel (500 ppm sulfur) used in off-road applications by 2011 as well. But reducing the sulfur also reduces its lubricity, which is beneficial to the injectors. The refineries put lubricity additives into ULSD, but the water in biodiesel/ULSD blends may quickly negate the positive effects of the lubricity additives unless dealt with aggressively by the filter system.

    The particle size to which fuel should be filtered is small and must be balanced against the risk of filter plugging. (For more on how you define filter efficiency see “Shoptalk: defining filter efficiency,” on page 88.) “Filter plugging depends on how you balance your system; having a two filter system where the filters work together,” says Matt Stein, liquid filtration manager for Donaldson. “But in general, everybody is driving for high-efficiency filters and developing new media to handle that.”

    When a filter plugs up, some customers blame the filter, Stein says. “But obviously, there is a contaminate that’s causing it, probably originating in the bulk fuel,” he says. “If the filter is plugging, it’s doing its job.”

    Tracing contamination
    Diesel fuel comes out of the refinery pure, but through storage and transport, it picks up water and particulates, Brisk says. “In our tests we’ve found that up to 40 percent of the fuel we’ve sampled is of poor quality. Fuel filtration before you get it in the vehicle is important,” he says. “We’re seeing a trend towards fuel filtration being almost as clean as hydraulic filtration, going down to five microns or less.”

    Keep in mind that biodiesel or ULSD, if properly managed, may not require a filter change. “Whenever there is something new it creates confusion and an opportunity for people to sell new stuff,” Stein says, “but that doesn’t mean you need new stuff. Fuel quality is the key. If you have fuel from a good source and are storing it properly, you’re not going to have water issues.”

    Two part solution
    If you’re required to use biodiesel and encounter excessive fuel filter plugging or water in your fuel, you need to take a two-prong approach. First, review your bulk storage and handling procedures to help eliminate the source of contamination. Most guidelines recommend you store biodiesel blends no longer than 90 to 120 days. There are also additives you can put in the fuel to help control water.

    If that’s impractical or doesn’t eliminate the problem, discuss upgrading your fuel filters with your filter supplier or your equipment manufacturer. You can usually bolt-on an aftermarket fuel coalescer that works with your existing fuel filters or switch to a more robust fuel filter system. But, as with any modification to a machine, consult first with your equipment or engine dealer.

    Many on- and off-highway diesel engines today pump recirculated exhaust gas in the combustion chamber to reduce combustion temperatures and curb emissions. But one of the side effects of this EGR technology is it raises soot levels inside the engine. New lube oils were formulated to better keep this soot in suspension, but the lube oil can only do so much.
    “On severe duty-cycle applications, a lot of engine manufacturers have significantly reduced engine oil drain intervals because of soot,” says John Clevenger, general manager for strategic alliances with Cummins Filtration. “Better filtration, capable of removing both organic and inorganic contaminants, can improve the oil’s life,” he says.

    Soot’s challenge
    Inorganic contaminants are things like dirt, wear metals and disintegrating gasket material. Organics consist of unburned fuel, additive drop out and soot. Ordinary pleated filters do fine filtering inorganics, Clevenger says. But you generally need better filtration such as depth media or centrifuges, to take out the organic contamination.

    Soot is extremely hard and abrasive, but submicron in size – so small no filter can trap it as pure soot. The new oil formulations keep it in suspension longer, but soot eventually attaches itself to other, larger organic particles to form what Clevenger describes as “abrasive slime.”

    There are two filter technologies that help deal with abrasive slime: centrifuges and depth media. These are usually set up as bypass filters – separate filters that take about 10 percent of the total oil available in the system and super-clean it before returning it to the sump, thus continually diluting the dirty oil with clean.

    Give it a spin
    “Centrifuge filtration has been around a long time,” says Paul Ewing, national accounts manager off-highway, at Luber-finer. And while it’s not necessarily a solution for every high soot condition, centrifuge filters are growing in popularity for some on- and off- road applications, he says. Large dozers, because of their heavy loading, tend to dump a lot of soot into the oil quickly. And the managers of big mining equipment often favor centrifuges because of the expense of rebuilding engine components and the desire to avoid service related downtime.

    The initial cost for a centrifuge is as high as $3,000, plus the labor to install it, Ewing says. “That’s why I caution you should make sure you need it, that you have a high soot condition. Sometimes you can take care of that with a straight bypass filter or spin-on filter. I’ve had D-11s go with a more economical, high efficiency filter and maintain 500-hour lube change intervals.”

    Also keep in mind that soot buildup isn’t necessarily the condemning factor for your lube oil. “On road we don’t see soot as the driver for oil change intervals,” says Keith Bechtum, liquid filtration product specialist for Donaldson. Depleted additives and/or a lowered TBN (total base number) more typically force the oil change even when the soot level is still acceptable. With off-road engines, he says, soot is more frequently a condemning factor.

    Get good oil analysis
    Oil analysis is the best way to determine if you have a soot problem, but that oil analysis must include a particle count to determine soot levels. Particle counts, however, are often considered extras and rarely included in free oil sample programs. “A free oil sample might not tell you much,” Clevenger says. “Get good oil analysis with a particle count and consider paying for it.”

    The decision to use centrifuges or depth media to control soot depends on the customer’s goals, Clevenger says. “Do you want extended drain intervals, longer equipment life, or just the cheapest product you can get away with?” Extended service intervals are popular. Recently, though, because the engines and equipment have become more expensive, people are starting to talk more about extending their equipment life, he says.

    Drain intervals, engine life
    In trying to save maintenance costs through extended drain intervals, many equipment managers will pay extra for synthetic or high performance oils. If this is one of your goals, keep in mind that even the best oils can’t extend drain intervals in a high-soot application. Also remember that high-performance oils go hand-in-hand with high-performance, extended-life lube oil filters with synthetic media. In addition to giving you increased flow characteristics and finer particle filtration, these high performance filters are designed so that the seals and gaskets don’t deteriorate before the oil does.

    To meet the Tier 3 emissions regulations that came due in 2002, Caterpillar introduced a different (non-EGR) technology called ACERT or advanced combustion emissions reduction technology. According to Frank Scherbing, with Cat’s filter and fluids sales support group, ACERT engines have variable valve actuators operated as solenoids which precisely control air intake and exhaust for more complete combustion. To keep the engine oil cleaner and extend the overall engine life to overhaul Cat also switched from a 35-micron lube oil filter to one that filters down to 22 microns. Scherbing adds that a 100-percent synthetic, 11 micron “ultra high efficiency” filter is also available for customers who want to maximize lube oil cleanliness.

    All 2007 and later model on-highway truck engines come with a diesel particulate filter that traps and burns off exhaust gases much like a catalytic converter. These filters clean themselves in one of two ways. At high exhaust temperatures the particles trapped in the filter are oxidized via precious metal catalysts and available exhaust heat. And for engines that don’t reach these high temperatures a fuel injection scheme raises the temperature to a level that burns the captured soot.

    In either event, some ash residue is left behind in the filter and needs to be cleaned out periodically. The EPA has mandated that these devices be able to go at least one year or 150,000 miles between cleanings. DPFs are somewhat large, about a foot or so in diameter and roughly 18 inches long and in some cases may require two technicians to remove, clean and reinstall.

    New engines, new procedures
    Three practical maintenance items to keep in mind if you purchase a 2007 truck with a DPF is that you cannot put used oil in the fuel of these engines (as sometimes could be done with older models). This will cause excessive ash to form in the filter and shorten the service life. Second, you should avoid burning anything but ULSD in these engines, as the sulfur will likewise cause the filter to plug up prematurely. Finally, most engine manufacturers are recommending the use of the new low-ash CJ-4 lube oils in these engines to likewise keep ash deposits to a minimum.

    Another big change for exhaust filtration is occurring in older trucks and off-road equipment in regions where air quality is poor. The state of California has mandated exhaust filter retrofits for trucks, buses and off road equipment running Tier 0, 1 or 2 engines, and areas in New York, New Jersey, Massachusetts and Connecticut are starting to follow suit, says Fred Schmidt, director of sales for emissions retrofits at Donaldson.

    Retrofitting older equipment
    “We see the off-road retrofit emissions market as an emerging market,” says Gary Reeves, Donaldson’s director of product management for exhaust and emissions products. “It was preceded by a lot of on-road retrofit activity and it’s still in its infancy right now.”

    The California Air Resources Board is calling for the “best available” technology in retrofitting older model diesel engines. The above-mentioned DPFs work fine for retrofitting newer on-highway truck engines. But off-road equipment and applications vary considerably and create more soot and NOx emissions compared to on-road. CARB is working on a rule that will require reductions in both types of emissions.

    “We have several technologies,” says Judy Murphy, project manager, emissions solutions, Cummins. “Any technology we apply to on road can be applied to off-road applications as long as the requirements are met. A lot depends on the location of the exhaust, the fuel constraints and things like vibration. If a higher level of after-treatment does not work due to the duty cycle, we have other products that can be applied.”

    Good, better, best
    The lowest level of technology allowed is what’s described as a CARB Level 1 control. This is typically a diesel oxidation catalyst, which eliminates at least 25 percent of the particulate matter (PM) in the emissions. DOCs are easily applied to off-road applications, accommodate high sulfur fuel levels and are smaller and easier to mount than other types of exhaust filters. CARB Level 2 devices take out at least 50 percent of PM emissions and typically combine a DOC with a metallic filtering substrate. CARB Level 3 devices are DPFs (the same as used in 2007 on-highway engines) and filters out greater than 85 percent of emissions.

    Level 3 retrofits for on-road engines have been in existence for about five years, Murphy says. “We’re just starting to move into the off-road markets with Level 3. We’ve done some off-road retrofits, but they’re at the demo level now.” Off-road applications present unique challenges to DPF installations.

    Their size presents mounting and line-of-sight problems. They’re also heavy and subject to vibration stresses. Management of higher exhaust temperatures is also a factor. And in some areas contractors can’t yet get the ULSD fuel necessary for the DPFs to perform properly. Despite these challenges, DPFs will become more prevalent in off-road equipment as the industry moves toward Tier 4 EPA regulations beginning in 2011.

  • Shop talk: defining filter efficiency
    Talking about the micron size of contaminants seems fairly straightforward. A human hair is about 70 microns wide, white blood cells are 25 microns, tobacco smoke particles measure a tiny half micron. Fuel filters should remove particles down to five microns in size (some say two). Engine lube filters should take out anything larger than 30 microns.

    But in the real world, things aren’t quite so simple. Micron ratings don’t tell you the efficiency of the filter or how well it holds contaminants over time. To measure these attributes the industry came up with what it calls multi-pass testing or beta-ratio testing. According to the Filter Manufacturers Council, in a multi-pass test a fluid containing contaminants of a known size and quantity is pumped through a filter numerous times (hence the multi-pass) and then analyzed to determine how many particles of a given size remain after filtration. Dividing the number of particles upstream of the filter by the number of particles downstream (the clean side) gives you the Beta ratio – a measurement of the efficiency of the filter.

    Without going into a lot of math, here’s how Beta ratios equate to efficiency:

    Beta ratio Efficiency
    2 50 percent
    10 90 percent
    20 95 percent
    75 98.7 percent
    100 99 percent
    200 99.5 percent
    1,000 99.9 percent

    So when comparing filters it helps to know the Beta ratio. A filter that claims to handle particles down to 2 microns in size does you no good if its Beta ratio is 2 and it’s only capturing half of the particles that size.