Maintenance/Management: Dealing with dust
| June 12, 2007 |
Heavy equipment engines may be massive and powerful, but all it takes is a teaspoon of dust to ruin one. Silica, the primary ingredient in dust, is highly abrasive and acts like a lapping compound – polishing your piston rings, valves, cams and crankshafts and sandblasting your fuel injectors or any moving part with tight tolerances.
Fortunately today’s heavy equipment air filters do a fine job of cleaning the intake air before it reaches your combustion chambers. But because of the speed and ease with which contamination can damage an engine it is crucial that you approach the servicing and maintenance of your air filters with surgical precision and cleanliness. A few careless mistakes can have big consequences.
“With the new Tier 3 and the upcoming Tier 4 engines, the tolerances are tighter and air quality is more important,” says Tom Miller, who is in charge of air product management for Donaldson.
“With the new engines coming out you have turbos that push greater volumes of air through the engine and higher pressure fuel systems,” says Guy Moret, global product director for air and crankcase ventilation at Fleetguard. “All of this is creating an engine environment that is much more sensitive to dust contamination.”
“People are getting more cognizant of air filtration,” says Pathikrit Banerjee, marketing manager for air technology business at Fleetguard, “and it is getting more sophisticated for various reasons.”
Anatomy of an air filter
Most construction machines today use a two-stage filter: a larger outer primary filter and a smaller secondary or safety filter inside that. The secondary filter is not there to polish the air or add additional filtration during normal operation, but to protect the engine should the primary filter become damaged and to keep dust out of the engine when you’re changing the primary element. Since it’s protected inside the primary filter, the secondary filter is changed far less frequently than the primary. On average you’ll change the primary filter three times before the secondary filter needs changing, says Wayne Mellgren, manager of field services for Donaldson.
The contaminant removal efficiency of the inner filter is much lower than that of the outer, says Travis Winberg, service engineering supervisor for Baldwin Filters. The reason is that the inner air filter has a lot less surface area of media than the outer filter and has to provide the same airflow as the outer.
Gauge it, don’t eyeball it
Restriction gauges are found on many off-road air filters and are the best way to tell when your primary filter has become too clogged with dust and dirt. Without a restriction gauge you’re forced to remove the primary filter from its housing and visually inspect it, a procedure that may allow contaminant to fall to the clean side of the filter, Winberg says.
Restriction gauges come standard on many filters, and are mounted to the filter housing or the air duct near the housing and need only be replaced if they get damaged, says Steve Merritt, director of air filter engineering at Baldwin. And you can usually install one as an aftermarket part on a filter that doesn’t have one. They range in complexity from simple screw-in gauges to sophisticated electronic monitors. Larger, more expensive, more critical equipment tends to get the more sophisticated gauges that are wired to alarms or indicators in the cab. These can be helpful in severe dust environments where checking a gauge in the engine compartment may only happen once a day and can prevent an operator from running a piece of machinery for hours with a clogged or damaged air filter, Miller says.
And once you’ve blown out a filter and returned it to service you have to remember that filter will never get back to a like-new performance level, Moret adds. So you’re starting from a worse point every time you do this. “It’s not something we endorse,” he says. The issue comes down to this, Moret says: “Do you want to change your filters often or do you want to change your engine often?”
Catching the big particles
Precleaners can be a useful addition to your air filter program, particularly in high-dust environments. Precleaners remove contaminant through mechanical separation and do a relatively good job of removing large particles, Merritt says. By removing the large particles precleaners increase the life of the primary filter. Precleaners are mounted upstream of the primary filter either in the filter housing or in a separate housing. Most precleaners are maintenance free, Merritt says, but some models have a reservoir to hold the contaminant and these must be dumped periodically.
What makes precleaners a wise investment is that they remove up to 80 percent of the contaminants and they can extend the life of your primary filter by a factor of four or five, Miller says.
Most air filter housings today are made of lightweight plastics. Metal housings were once the norm because the rigidity of the metal container was necessary to compress the gasket that seals the filter to the engine mounting block. But with the design of what the industry calls a “radial seal,” essentially a sleeve that fits over a tube, the need for rigidity was eliminated and plastics took over in all but a few applications. You’ll occasionally see steel housings in equipment that experiences heavy shock loads, Miller says. There are also high-temperature plastics for high-heat applications and some hybrid designs with plastic bodies and metal end covers.
Although it may look bad, an air filter caked in dust may in fact be filtering air better than one that’s brand new. “Dirt on the surface of the media becomes another filter,” Miller says. “An element that looks dirty could have pretty low restriction yet.” Accordingly, the restriction gauge is the only reliable means of determining when it’s time to change a filter, he says. Appearance doesn’t matter and neither does the time the filter has been in use. If enough air is flowing through you should leave it alone.
One of the worst things you can do is to take the primary filter out for unnecessary inspections. Every time you open the filter housing you introduce the possibility of contamination getting into the engine. It only takes a light tap to send an airborne cloud of dust flying over the engine and contaminating the clean side of the filter.
In dusty environments it’s not uncommon to see operators or service technicians remove a primary filter and tap it on a bumper or tire or blow it out with an air compressor and reinstall it. Again Miller and Mellgren advise against the practice. First, just tapping the filter on a solid object creates enough shock loading to possibly tear the filter media, Mellgren says. Blowing out a filter with compressed air is not quite as bad, if you blow from the inside out. But it’s still a less than pristine operation and also runs the risk of tearing the media.
“We ran a study once with one of our major customers because they were questioning whether or not they should clean their air filters,” Miller says. “We had a reputable cleaning outfit clean their filters with compressed air in a controlled environment and 60 percent of them came back damaged.”
Watching the gauge
With a restriction gauge to guide you, filter replacement is just a matter of waiting until the gauge says so. And thanks to today’s electronically controlled engines you may not need to immediately switch the engine off and change the filters, Miller says. “As the engine gets less air it tends to have less power and use more fuel, but the reality is that today’s electronically controlled engines will run past that with hardly any detraction in performance,” he says. “I’m not making recommendations beyond what the engine manufacturers do, but it’s usually not a critical thing the second the gauge trips.” So it’s fairly typical for the people who are servicing by restriction levels to wait until the end of the shift to service the air filter, Mellgren says.
One thing to watch for, however, is if your gauge indicates a sharp increase in restriction. That usually means the primary filter has been compromised and that the secondary filter is rapidly clogging up, in which case you’d want to get an immediate replacement.
Fitting into the future
With the coming of the new Tier 3 and Tier 4 emissions compliant engines, many manufacturers are increasing the size of their cooling packages. Additionally, many are sloping the front hoods on their machines for better sightlines and stylish looks. The end result of both these trends is less room under the hood for componentry, air filters included.
Filter manufacturers are responding by designing smaller filters that maintain the same air flow and life expectancy of the filter.
Another technology to look for is long-life filters, Winberg says. The long-life versions provide more contaminant holding capacity and give you more time between service intervals in high dust environments.