LO 10-5 Identify and describe the types, functions, construction features, and applications of diesel engine lubrication system components

1.10. Oil Filter

Oil Filter

The purpose of lubrication-oil filtration is contamination removal. Oil contamination can allow abrasives to rapidly wear engine components if not properly controlled. Soot, sludge, and dirt are the most common contaminants removed by the filtration system. The choice of filter capacity and type of filter media are determined by the degree of cleanliness desired for the lubrication oil.

Filter Media
The type of filter media used inside the oil filter depends on a number of variables, including particle-removal efficiency, contaminant holding capacity, resistance to flow, and the corresponding pressure drop of a full filter. There are between 50–75 different media grades designed for oil filtration that are available to filter manufacturers Figure 46. Media used for air, coolant, and oil filtration cannot be used interchangeably. Types of oil filter media range from mesh-like screens to thread or chopped paper to 100% natural cellulose and 100% synthetic microfibers.

A	B		FIGURE 10-47: Cutaway of a bypass filter that uses cellulose-microglass filter media. Unfiltered oil enters the case on the outside of the filter and must pass through the filter media to the filter center. The bypass filter has two different types of media supplied with one inlet but two separate outlets.
FIGURE 10-46: Two oil filters. A. Paper filter with yellow media. B. Microglass filter with white media.

When only large particles are to be removed, a cellulose or paper media is used. To remove progressively smaller particles, the type of media changes from complex cellulose to blended media containing cellulose and microfiber materials. Cellulose or paper typically provide filtration of particles larger than 13–20 microns. Glass microfiber, or microglass, provides the most efficient filtration with the least amount of restriction, but it is usually the most expensive to manufacture. Microglass filtration is capable of removing particles as small as 2–5 microns Figure 47. Pleated filters provide more surface area for holding contaminants; however, too many pleats can swell and prevent oil flow.

Because diesel engine oil contains a substantial amount of soot, more than one filter is used, and bypass filters are commonly used in addition to the full-flow filters that supply oil directly to engine bearings Figure 48. Bypass filters supplement regular filtration by filtering oil and returning it to the oil pan. Paper depth filters and spinner or centrifugal bypass filters are commonly used. Centrifugal bypass filters often use a replaceable paper filter that separates soot by spinning a filter core at high speeds, using oil pressure to drive the spinner core Figure 49. The thin paper, which is replaceable in many bypass spinners, traps and separates soot from oil.

FIGURE 10-48: This engine uses two full-flow filters and one bypass filter.

FIGURE 10-48: A centrifugal bypass filter removes soot using a high-speed centrifuge driven by engine oil pressure.