Why do valves with rubber seats keep leaking? It is the peeling of the sealing layer that is the real \"culprit\"”

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Why do valves with rubber seats keep leaking? It is the peeling of the sealing layer that is the real culprit. Rubber gate valves are widely used in water supply and drainage, municipal engineering, construction, and industrial applications; they offer good sealing properties, low flow resistance, corrosion resistance, and are not expensive. But over time, it began to leak. Many people thought it was due to aging of the valve seat, but in reality, the true cause is often not as simple as aging. The core sealing element of a rubber gate valve is the rubber sealing layer lining the valve disc, which functions as the \"heart\" of the valve. Once there’s a problem with this “heart,” the valves become useless. The failure of rubber sealing layers mainly takes three forms: detachment, wear, and tearing. Seal layer detachment: the most severe form of failure. Detachment refers to the complete peeling away of the rubber seal layer from the metal frame of the valve plate. The valve immediately lost its sealing ability; it couldn’t be closed properly, nor could it be opened smoothly. Why does it fall off? The most fundamental reason is a defect in the bonding process. The rubber lining of the valve plate is usually bonded to the metal frame by molding and vulcanization or with adhesives. If the metal surface is not properly prepared before bonding – if sandblasting is inadequate, there is oil or rust on the surface, or the primer is not applied properly – it will significantly affect the bonding strength. Improper control of temperature, pressure, and time during the vulcanization process can also lead to insufficient or excessive vulcanization of the rubber. There is another reason that is easily overlooked: the thermal expansion coefficients of rubber and metal differ greatly. The thermal expansion coefficient of rubber is much higher than that of metals; when the temperature of the medium fluctuates frequently, significant thermal stress is exerted on the bonding interface. Over time, the adhesive layer suffers from fatigue-induced microdamage, gradually develops cracks, and eventually comes off entirely. Furthermore, certain chemical agents (such as oils, strong oxidizers, and organic solvents) can penetrate the bonding interface, corroding the adhesive or the rubber itself and resulting in a decrease in adhesion strength. Especially in areas where the bonding edges are defective, the medium can more easily penetrate, causing a \"filament effect\" and an expanding range of detachment. Seal layer wear: Gradual performance degradation. Wear occurs more slowly than detachment, but it is just as fatal. The sealing layer is gradually worn thin, losing its smoothness and evenness, which results in a poor seal. The most common cause is solid particles in the medium. When sediment, rust, and mineral dust flow at high speed over the sealing surface, they act like sandpaper, grinding the rubber surface. The harder the particles, the sharper their edges, and the higher their concentration, the faster the wear occurs. Another reason that many people are not aware of is \"cavitation\" – when the local pressure at the throttling part of the valve is lower than the saturated vapor pressure of the liquid, bubbles form in the liquid. These bubbles burst instantly when they reach areas of higher pressure, generating extremely high shock waves. These shock waves repeatedly strike the sealing surface, causing the rubber layer to develop honeycomb-like defects and accelerating wear. During the opening and closing of the valve, there is also relative sliding between the rubber sealing surface of the valve disc and the metal sealing surface of the valve body. If the medium has poor lubricity, or if the valve is opened and closed too frequently, this frictional wear can also be quite severe. Seal layer tear: localized structural failure. The tear usually starts at a stress concentration point and then spreads rapidly. In the most common cases, the valve is stuck in a state close to being fully closed by hard particles such as stones or welding slag; the operator is unaware of this and attempts to close the valve forcefully, and the resulting high shear force tears apart the rubber layer. Using improper tools to strike the valve plate during installation or maintenance can also cause localized tearing. How to prevent and solve it? The bonding process must be strictly controlled. The metal surface must be thoroughly descaled by sandblasting and cleaned, and the primer must be applied evenly. The vulcanization temperature, pressure, and time must be precisely controlled; there is no room for approximation. The material selection must match the operating conditions. For media containing particles, a rubber material with good wear resistance should be chosen ； For media that are corrosive, corrosion-resistant rubber should be used. Rubbers of different materials exhibit significant differences in performance: NBR nitrile rubber has good oil resistance, EPDM ethylene propylene diene monomer rubber has good weather resistance, and FPM fluororubber can withstand high temperatures and corrosion. Installation and maintenance must be carried out in a standardized manner. Do not strike the valve plate with tools; the pipes must be thoroughly purged before installation to remove weld slag and rust. Operate the valve smoothly; do not close it forcefully. If the rubber sealing layer has come off or torn, there is little possibility of repair; either the valve plate must be replaced or the entire valve must be replaced. Pay more attention in daily use, address issues early, and don’t wait until it’s completely broken before replacing it.