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When a collapsed center tube or element is discovered, the natural tendency is to assume something is wrong with the filter (Figure 1).
This is generally not the case, but instead is a symptom of problems with internal engine components.
Most engines incorporate a bypass valve across the inlet and outlet of the full flow oil filter within the lube oil system. The valve is designed to open and bypass oil around the filter and/or element when the restriction reaches its opening pressure (Figure 2).
The bypass flow circuit ensures oil flow to the engine when there is a significant restriction across the filter due to element plugging or cold start conditions. Typically, engine manufacturers design bypass valves to open at a pressure differential of approximately 10 to 30 psid with some as low as 4 psid (28 kPad), and others opening as high as 75 psid (500 kPad). Some engine manufacturers locate the bypass valve in the filter mounting base on the engine, while others locate the valve within the filter. Either way, the same purpose is served.
Oil filters are designed to withstand differential pressures significantly greater than those experienced under normal operating conditions. Therefore, when a center tube or element has collapsed, it is usually the result of a sticking or otherwise malfunctioning bypass valve.
In some instances, a sticky filter bypass valve alone is not enough to collapse the center tube or element. The oil pump pressure regulating valve may also stick in the closed position, which results in increased pressure and oil flow through the filter. Although this condition may be only momentary, it can quickly collapse the center tube if the bypass valve fails to, or is unable to, relieve the excessive differential pressure.
A collapsed center tube or element can lead to a loss of filtration and oil flow to the engine. There is the possibility that interior parts of the filter or filter media may be physically displaced and could migrate into the system interfering with the oil flow. Additionally, debris and contaminants that are held by the filter may be released.
The malfunction of the filter bypass and oil pump pressure regulating valves and the subsequent collapse of the center tube or element may not cause noticeable damage. However, at times it can result in a catastrophic failure of the engine caused by the seizure of a piston, connecting rod or main crankshaft bearings among other failure possibilities.
The malfunction of filter bypass valves and pressure regulating valves has been traced to:
Discovery of a filter with a collapsed center tube or element calls for the inspection of the bypass valve, if not built into the filter, and the oil pump pressure regulating valve, plus a review of the engine’s performance and maintenance history.
This technical service bulletin is reprinted with permission from Filter Manufacturers Council (www.filtercouncil.org.).