You may take your oil filter for granted, but this small, inexpensive part of your compressor's lubrication system plays a vital role in protecting the compressor from premature wear. Each moving part in the compressor requires clean oil for proper lubrication and lasting life. The oil filter cleans the oil as it passes through the filter element or filtering media. This prevents abrasive contaminants in the compressor lubrication system from damaging compressor parts.

The better you understand your compressor's lubrication system, the more you'll appreciate the vital role your oil filter plays. When the compressor is running, oil enters the oil pump through a screened intake. The oil is drawn through the screen intake and forced by the oil pump through the oil filter.

In a typical full-flow type oil filter, the oil flows into an inlet passage and then through the filtering element. After flowing through the filter element, the filtered or "clean" oil passes directly to the main oil gallery. In a partial-flow type filter, the oil returns directly to the oil pan.

There are two basic types of filter media: the "paper" media and the "depth" type media.

The primary features of the filter elements are:

Particle size retention (filtration efficiency)
Particle size retention is the measure of the degree to which the filter can retain particles of various sizes.

Dirt-holding capacity
Dirt-holding capacity is the amount of contaminant that can be removed and held by the filter until the filter ceases to function.

Resistance to oil flow
New arch-pleated, prescription-blended media, with a maximized number of pleats has less than 2 psi pressure drop when filtering oil at a rate of 4 g.p.m. at normal operating temperature.

Parts of an Oil Filter

Gasket - provides exterior seal between the filter and engine at the engine mounting surface.

Mounting Plate - prevents deflection (movement) at the gasket sealing surface. Heavy gage steel plate provides for threaded attachment to the engine.

Inner Element Support - provides inner element stabilization and a positive seal between the inner element and the mounting plate to prevent the bypass of unfiltered oil.

Upper End Cap - retains element end sealant and filter media, provides an outlet for clean oil, and provides structural rigidity to the pleated media.

Lower End Cap - retains element end sealant and filter media.

Arch-pleated, Prescription-blended Filter Media - provides a more than adequate filter area. The element has a controlled porosity blended media to assure complete filtration of the oil.

Spiral-wound Center Tube - provides internal element support. The spiral design greatly reduces initial flow restriction when compared to other designs.

Coiled Spring - ensures a constant load on the inner element to maintain the seal between the upper element end cap, the inner element support, and the mounting plate even during pressure surge situations.

Filter Canister - encloses the assembly with a mechanically-locked double seam. The canister provides "flutes" at the closed end for ease of removal with an oil filter wrench.

Silicone Anti-Drain back Valve - Stays flexible in extreme temperatures, improves oil flow and keeps oil in filter to prevent engine destroying dry starts.

Some filters include anti-drain back and/or filter by-pass valves. These types of filters are identical to full-flow filters, except that a by-pass valve replaces the inner element support and an anti-drain back valve has been added. The Anti-Drain back Valve prevents oil from draining out of the filter inlet holes when the engine is shut off. It also provides seal between clean and dirty oil at the upper end cap. This is necessary in applications where the oil filter is mounted in a horizontal or inverted position.

The Filter By-Pass Valve

If a full-flow filter becomes "clogged", or excessively restrictive to oil flow, the filter by-pass valve ensures continued engine lubrication by allowing the oil to by-pass the filter. Some manufacturers have the by-pass valve built into the oil filter mounting unit (located on the engine).

Other manufacturers require full-flow filters have the by-pass valve built into the filter itself. All oil filter types recommended for these particular applications include the by-pass valve assembly in the filter

By-pass Valve Assembly -- spring loaded valve assembly that allows oil to by-pass the element under high-differential pressure conditions such as cold oil and/or excessively contaminated media. This allows lubrication of the engine, but without full-flow filtration.