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Valve Seat Leakage Causes in Industrial Valves

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Valve seat leakage occurs when the sealing interface between the valve seat and closure element fails to provide complete shutoff, allowing unintended internal flow. It is typically caused by wear, erosion, corrosion, debris intrusion, improper installation, misalignment, over-torque, or thermal distortion affecting the sealing contact surfaces under operating pressure and temperature conditions.

Relative allowable leakage per class (qualitative)relativeClass IV(metal)Class V(metal)Class VI(soft)
Soft-seated Class VI allows effectively zero leakage; metal seats have finite allowances. Illustrative cross-section; not to scale.
Seat leakage means fluid passes the closed seatTight shutoff: no leakageSeat leakage: passes closed valve
A leaking seat allows process fluid to pass the closed valve into the downstream system. Illustrative cross-section; not to scale.