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It takes some juice to get through the shell of a quality oil filter. The strength of this shell is very important. If the shell is too thin or poorly joined at the base rupture can occur. Rapid loss of oil and pressure will result in engine damage. Measure of the shell strength is referred to as burst pressure.
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Removing the outer shell reveals the inner workings of an oil filter. Directly underneath the shell is the filter hold-down element or spring. The spring applies just the right amount of pressure to the filter cartridge to keep it sealed against the anti-drainback valve.
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The filter cartridge holds the pleated filtration material in place. This material is what catches and keeps crud from ruining the engine. The better the material the better the filtration. The material will eventually clog up as it cleans. This is why it is important to regularly change the oil filter.
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At the base of the filter cartridge is the anti-drainback valve. This valve holds oil in the filter when the engine is turned off to help provide quick lubrication to the engine when it is started once again.
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The pressure relief valve is shown open here. This valve is designed to open in case of oil pressure imbalance and prevent engine oil starvation by bypassing the filter cartridge. A severely clogged filter will cause this valve to open making the filter itself moot.
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At the bottom of the oil filter is the base. This is what holds the oil filter to the engine. Oil filter base gasket quality is extremely important. A base gasket rupture can spell the end of an engine in short order. Never over-tighten an oil filter, as this can cause the base gasket to fail.
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