A Look at Filter Media
Filter manufacturers continue their efforts to develop media that will meet the demands of today’s engines. Filter customers continue to demand products that will provide engine protection during maintenance intervals which continue to increase.
It is important to understand that filter media differences can be significant from one filter to the next. A spin-on or cartridge filter may be the same length and diameter as another filter, but this doesn’t mean that the filter will perform the same and protect your engine as the OE manufacturer has intended.
Baldwin Filters and other leading manufacturers use many different types of media for various fluids and environmental extremes. Overviews of the most common media are given below.
Cellulose-Based Media Overview
Cellulose and cellulose blends have proven over time to be the best media value for most lube, fuel and air filter applications. New technology has allowed the development of cellulose-based media that provides the best combination of life and efficiency in various applications and operating conditions.
Fleet test have shown that cellulose-media lube filters still have additional capacity and media integrity after 30,000 miles in normal applications. With cellulose-based media filters, maintenance managers can achieve their goals of longer maintenance intervals at the lowest cost without sacrificing engine life.
Glass Media Overview
Glass media was developed to be utilized in hydraulic systems because it has low flow restriction at high filtration efficiencies. These low flow resistance properties are beneficial in hydraulics where cold oil is being forced through the media and filtration in the 3-5 micron nominal range is desired.
Glass media has a drawback regarding capacity. Typically, this media has the same pore size and same fiber diameter through the entire sheet. The media can be manufactured to be very efficient, but then it is so tight that it has very little life or capacity. The media can be manufactured to be more open, but then the efficiency is lost. Remember that the low flow resistance properties of glass media are not as important in engine lube oil filtration. Engine oil tends to heat rapidly, so flow resistance is of little concern.
Why Is Cellulose Most Often the Best Choice?
In most lube, fuel and air filter applications, cellulose media is a better choice than synthetic media. Again, the reason largely relates to capacity, or filter life. To explain why, a description of the filtering process is necessary.
Cellulose media is manufactured with fibers of various sizes. On the top layer of the media, the fibers are fluffed up, rather than compacted down.
When fluid and contaminants are passed through the media, many particles collect on the fluffy fibers on the surface and don’t travel farther into the sheet. This is referred to as “adsorption” because the particles adhere to the fibers.
The more of this separation technique that a media applies, the more small particles can be separated before they reach the small pore spaces on the screen side of the media. This keeps these small particles from plugging the media.
Another advantage of cellulose media is that the media will typically be thicker. The thicker it is, the more time the particles spend traveling through the media. Each time the fluid changes direction around a fiber, the particles momentum keeps them traveling in the same direction they were going and they are driven into the fibers.
This particle separation is referred to as “impingement.” As with adsorption, the more impingement that a media applies, the more particles are separated without plugging the tight pore space on the screen side.
Synthetic media does separate some particles with adsorption and impingement, but the smooth fibers can’t hold the particles in place and they are washed off with the fluid traveling through the media. Synthetic media primarily uses the particle separation technique call “direct interception.” This is how most people think all filtering is done.
Direct interception is simply separating particles by passing the fluid through pore spaces that are small enough to catch them. However, once all pores are plugged with the contaminant, the filter is plugged and its life is over.
Because cellulose media is better at adsorption and impingement, it can remove more contaminants than glass media without plugging pore spaces.
Can a synthetic media be created with the benefits of cellulose media? This remains to be seen. The fact is that cellulose-based media and glass media both have a place in today’s filter market.