The bypass valve on a return line filter element 0660 R025 W/HC/KB is passive safety — it's there as a last resort to keep oil flowing if the element blocks completely. When it works correctly, it opens at the rated differential pressure, allows unfiltered oil to bypass, and signals to the operator that element replacement is overdue. The DCS receives the high differential pressure alarm, operators respond, element is changed. Normal maintenance event.

 

Two bypass valve failure modes both cause problems but in opposite ways. A bypass valve stuck closed allows differential pressure to climb past the rated opening threshold, potentially collapsing the filter element as described elsewhere. A bypass valve stuck open or opening at below its rated differential pressure passes unfiltered oil continuously without raising differential pressure to the alarm setpoint — the DCS shows no alarm, no indicator suggests a problem, and contaminated oil circulates through the system while the filter element sits with almost no flow passing through it.

 

Distinguishing a prematurely opening bypass valve from a properly functioning filter using DCS differential pressure data alone requires looking at the pressure value in context. A differential pressure reading that's unusually low — significantly below the normal operating differential for the current flow conditions — with no recent element change is suspicious. Normal loaded filter elements show a pressure differential that grows gradually over time. A pressure reading that drops suddenly from its recent trend, without an element change event logged, suggests bypass valve leakage has opened a low-resistance path around the element.

 

Cross-reference the differential pressure reading with oil cleanliness data from sampling. If oil samples downstream of the filter are showing degrading cleanliness while differential pressure remains low, bypass valve leakage is the most likely explanation. The two parameters together — anomalously low differential pressure plus degrading oil cleanliness — constitute a positive diagnosis for bypass valve failure.

 

 

YOYIK, located in the famous industrial city of Deyang, is a leading manufacturer of steam turbines, coal-fired generators and hydropower equipment parts. Relying on rigorous national standards, strong technical force, advanced equipment and scientific management, the company provides a full range of solutions from electrical equipment to hydraulic machinery. Cooperating with hundreds of power plants at home and abroad, YOYIK has demonstrated first-class products and services in technical transformation and overhaul projects, and has won wide market praise.

 

Yoyik can offer many spare parts for power plants as below:

 

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DFYLMY-2026-06-12-A