b'A Fluid Situationcan remove submicron particles from the airstream. To be effective, a filter medium will use high pressure and require high energy costs to force air through.Devices that use coalescing mediums as a mode of filtration need less energy and can last up to 10 years. The other filtration method uses noncoalescing medi-ums, which are fibrous mediums that must be thrown away once saturated. While these filters do not de-mand much energy, they are not very efficient and must be replaced continually.Oil mist requires specialized equipment for collect-ing wet particulate matter, along with a different type of filter. Filters created for dry particulates, such as dry grinding dust, quickly become clogged and ineffective if used for oil mist. Wet mist collectors pull mist-laden air into the bottom of a collector, where larger drop-lets can fall out before air is pulled into a filter medium. must work correctly to achieve the overall goal.Packed-bed, or coalescing, filters are most effectiveBecause oil mists and solid particulates do not be-for most oil mists. These filters capture tiny dropletshave the same, they require different approaches to on fibrous mediums, and the droplets then coalescecollection. Dust collection equipment made for weld into larger droplets. When enough liquid accumulates,fumes and other solid particulates is not effective it simply drains off the filter medium into a collector.against oil mist.These filters continue to work even when fully satu- The best way to determine if a system works effec-rated, and they continually clean themselves as liquidtively is to test the air that travels in and out of a collector. drains off. The collected metalworking fluid then canPacked-bed filters with multiple layers of tightly woven fi-be further filtered for reuse. bers work well for both mechanically and thermally gen-erated oil mists.Fantastic Fan Packed-bed filters can handle some dry-soluble par-Using the right fan is critical to eliminate 80% of theticulates, which simply wash away with liquid as it co-problems behind mist control. When the people whoalesces. However, if a process generates large amounts design the equipment do not use the correct fan, theyof nonsoluble particles that mix with oil mist in the air, miss the right amount of pressure, the right ductworkyou may need to consider a pre-filtering process.or the right airflow to capture mist. If a fan does notThere are different approaches to separate solid par-move the right amount of air, mist in a machine will notticulates and liquid oil mists. Disposable pre-filters can be evacuated properly. Every component of a systembe used to strain out large solids before oil mist reaches 54APRIL 2020ShopSafety.indd 54 3/16/20 4:56 PM'