INTAKE AIR
Consider this: In the course of burning one gallon of diesel fuel a typical engine will consume more than 8,000 gallons of air. And should that engine inhale as little as a teaspoon of dirt over any length of time, it will soon begin to show signs of accelerated wear and premature failure.
That makes your machines’ intake air filtration a critical first line of defense against contamination. To enable off-road machines to breathe cleanly amid all the dust kicked up on a jobsite, most manufacturers offer three layers of air filtration. This starts with a pre-cleaner – a cyclone separator or multi-tube pre-cleaner that drops out or ejects 75 to 95 percent of the heaviest airborne particles. Next downstream is the main filter, which stops 99.9 percent of the remaining dust, followed by an inner, secondary or safety filter.
There is some misunderstanding about what these different layers of filters do, says Tom Miller, director of air product management for Donaldson. “The safety filter isn’t a polishing layer or part of a two-stage filter like some people think,” Miller says. “It doesn’t add to the filtration capacity. It’s there in case there is a failure of the primary filter – either a filter that had a breach in it or a filter that was installed wrong. It also protects the induction system when the primary filter is being changed.”
Air filter maintenance is also sometimes misunderstood.
Filtration experts all describe their worst nightmare: a guy pulling a primary filter off an engine, knocking it on a fender to loosen up the dust – or blowing it out with an air compressor – and then re-installing it. Although not uncommon, this practice is guaranteed to send that engine to the rebuild shop much earlier than necessary. Knocking dust out of a filter or blowing it out with compressed air immediately allows dust to accumulate on the clean side of the filter. And blowing compressed air onto a filter may remove a lot of dust but it also forces some dust more tightly into the fabric of your filter media, thus increasing your restriction.
There are several types of pre-cleaners. The tube-type pre-cleaners found on haul trucks collect dirt in a bowl that you simply empty when full. But the two-section designs that scavenge by an ejector muffler or rotating vane type pre-cleaners don’t require any maintenance, Miller says.
The first rule of air filter maintenance is the less frequently you change it, the better. Every time you open the compartment up you introduce contamination. Some people change the primary air filter when they change the oil filter, Miller says, but you really shouldn’t. Wait until the restrictor gauge tells you it's time to change and not before. You can’t tell when a filter is clogged just by looking at how dirty it is. And if you change air filters too frequently you’re actually putting more contamination into the engine since the filter is least efficient when it’s brand new. “Service by restriction,” Miller says, “not by scheduled maintenance.” The safety filter, as a general rule, only needs changing during every three or four changes of the primary filter.
Update on filters
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