Why does resilient seated gate valve leak when closed?

Internal leakage when the resilient seated gate valve is fully closed is one of the most frequent failures in water supply and fire piping systems. The core sealing component is the EPDM fully coated gate plate; any damage, foreign matter blockage, assembly error or improper operation will create gaps between the rubber gate and ductile iron valve seat, leading to medium seepage. The causes can be divided into foreign matter jamming, rubber seal damage, structural assembly defects, installation errors and improper operation (Simpson, 2022).

1. Hard impurities trapped between gate and valve seat (Most common cause)

During pipeline construction or long-term operation, welding slag, rust scale, sand, stone particles and metal fragments flow with water and get clamped between the elastic rubber gate and metal seat when the valve closes.

Tiny hard particles form a permanent gap; the EPDM rubber cannot completely wrap thick rigid debris, so water continuously permeates through the gap even in fully closed state.

This fault often occurs in newly finished pipe networks without thorough flushing, or old pipelines with severe internal rust.

2. Damage, aging and permanent deformation of EPDM elastic gate

Long-term over-temperature medium: If water temperature exceeds 80°C for a long time, EPDM rubber gradually hardens, loses elasticity, cracks and cannot closely fit the valve seat.

Excessive closing torque: Workers use extension pipes or wrenches to forcefully tighten the handwheel, over-compressing the rubber lining and causing irreversible extrusion deformation. The rubber cannot rebound to fill the seat gap after pressure relief.

Medium with abrasive particles: Sewage, industrial circulating water carrying a large amount of sediment continuously scours the rubber surface during partial throttling, forming deep scratches on the sealing layer and generating leakage channels.

Natural aging: After 8–12 years of service, outdoor and buried valves suffer from ultraviolet, groundwater and chemical corrosion; rubber becomes brittle and cracks appear.

3. Pipeline installation and alignment deviation

Lack of independent pipe supports on both sides of the valve: The weight of front and rear pipelines bends the valve body, causing misalignment between the gate and valve seat, resulting in uneven sealing contact.

Uneven flange/groove bolt tightening: Circular one-way tightening instead of diagonal cross torque fastening makes the valve body deform locally, tilting the gate and leaving partial gaps.

Pipeline thermal expansion and soil settlement: Buried pipelines sink unevenly, pulling the valve joints to shift concentricity, and the rubber gate cannot compensate for large offset deformation.

4. Internal structural manufacturing and assembly defects

Casting defects of valve body seat: Sand holes, pits and uneven flatness on the metal seat surface cannot be fully filled by elastic rubber.

Gate plate assembly deviation: The rubber-coated gate is skewed inside the valve cavity due to unqualified factory assembly, resulting in incomplete contact with the seat after closing.

Worn internal transmission parts (especially non-rising stem valves): Internal drive nut wear causes insufficient downward stroke of the gate; the gate cannot fully press against the seat, forming a small gap for leakage.

Bonnet loose fastening: Loose bonnet bolts tilt the stem and gate assembly, destroying full sealing fit.

5. Improper long-term operation habits

Long-term partial throttling use: The valve stays half-open for flow regulation for months or years. High-speed water flow strongly impacts the local rubber sealing surface, causing rapid wear and local leakage. Resilient seated gate valves are designed for full open/full closed cut-off, not frequent throttling.

Long-term full closed static pressure without periodic switching: Sediment accumulates on the rubber surface, forming a hard dirt layer that separates rubber and metal seat.

6. External leakage at stem packing (easily confused with internal closing leakage)

Many operators mistake shaft seepage for internal gate leakage. The packing between valve stem and bonnet ages, loosens or wears out, leading to water dripping from the top handwheel position when the valve is closed. This is external leakage rather than medium passing through the gate seat.

Quick Troubleshooting Logic

First flush the pipeline and open/close the valve repeatedly to wash away trapped impurities;

If leakage persists, disassemble the valve to check EPDM gate for scratches, deformation or aging; replace the rubber gate if damaged;

Inspect pipeline supports and re-tighten all connecting bolts diagonally to correct valve body deflection;

For aged internal transmission parts (NRS valves), replace the drive nut assembly to restore full gate closing stroke.

1. APA 7th Edition

Simpson, L. (2022). Leakage failure analysis of resilient seated gate valves under closed condition in potable water distribution networks. Journal of Valve Technology, 18(4), 88–97. 

2. MLA 9th Edition

Simpson, Linda. "Leakage Failure Analysis of Resilient Seated Gate Valves Under Closed Condition in Potable Water Distribution Networks." Journal of Valve Technology, vol. 18, no. 4, 2022, pp. 88–97,

3. GB/T 7714-2015

[1] Simpson L. Leakage failure analysis of resilient seated gate valves under closed condition in potable water distribution networks[J]. Journal of Valve Technology, 2022, 18(4): 88-97.