Mechanical failure
1. Wear of valve core and sealing ring
During long-term use, the valve core and sealing ring are constantly eroded, rubbed and corroded by the fluid, resulting in surface wear, scratches or dents, which makes the sealing surface not fit tightly and leaks. For example, when conveying media containing solid particles, such as slurry, sewage, etc., solid particles will flow with the fluid and hit the surface of the valve core and sealing ring, aggravating the degree of wear.
2. The clearance between the valve body and the valve core is too large
During the manufacturing or installation process of the ball valve, if the clearance between the valve body and the valve core does not meet the design requirements, the valve core will be offset during the rotation process, and the sealing surface cannot be fully fitted, causing leakage. Excessive clearance may be caused by insufficient processing accuracy, improper assembly or deformation of parts.
3. Deformation or looseness of valve stem
When the valve stem is subjected to excessive torque, vibration or external force, it may be deformed or loosened. Deformation of the valve stem will cause the valve core to rotate poorly and the sealing surface cannot be accurately aligned; loose valve stem will cause the valve core to shift during the closing process, affecting the sealing effect. For example, in situations where the valve is frequently opened and closed or subjected to severe vibration, the valve stem is prone to loosening.
4. Improper installation or aging failure of the sealing ring
If the sealing ring is installed in the wrong position, twisted or insufficiently compressed, the sealing performance will be reduced. In addition, the sealing ring will lose its elasticity due to aging, hardening, cracking, etc. during long-term use, and cannot effectively fill the gap between the valve core and the valve body, causing leakage. Seals of different materials have different service lives and application ranges. For example, polytetrafluoroethylene seals are prone to aging in high temperature environments, and rubber seals are prone to expansion and deformation in oil media.
Influence of medium factors
1. Excessive medium pressure
When the medium pressure exceeds the design pressure of the ball valve, it will generate excessive thrust on the valve core and the sealing ring, causing deformation or damage to the sealing surface, thereby causing leakage. For example, when there is a sudden pressure fluctuation or overpressure in the pipeline system, the ball valve may not be able to withstand the high pressure and cannot be closed tightly.
2. Abnormal medium temperature Changes in medium temperature will cause the ball valve components to expand and contract, thereby changing the matching clearance of the sealing surface. In a high temperature environment, the sealing ring may lose its sealing performance due to softening and decomposition; in a low temperature environment, the sealing ring may crack due to hardening and embrittlement.
For example, in a steam pipeline system, high temperature steam can soften the polytetrafluoroethylene sealing ring, resulting in sealing failure; in a liquefied natural gas (LNG) pipeline, low temperature medium can embrittle the rubber sealing ring and cause leakage.
3. The medium is highly corrosive. When conveying corrosive media, such as acid, alkali, and salt solution, the valve core, sealing ring, and valve body of the ball valve will be corroded, resulting in surface corrosion pits, holes or perforations, thereby destroying the sealing performance.
For example, in the chemical industry, ball valves conveying highly corrosive media such as hydrochloric acid and sulfuric acid are prone to loose closing if the selected materials have insufficient corrosion resistance.
4. The medium contains impurities. The solid particles, fibers, welding slag and other impurities contained in the medium will be embedded between the sealing surfaces during the valve closing process, hindering the close fit between the valve core and the sealing ring, thereby causing leakage. For example, in a newly built pipeline system, impurities such as welding slag and rust may remain in the pipeline. When the ball valve is closed, these impurities will be stuck between the sealing surfaces, causing the valve to not close tightly.
Installation and maintenance issues
- Improper installation position
The installation position of the ball valve should be convenient for operation and maintenance, and should avoid installation at the bends, dead corners or locations where the medium is easily accumulated in the pipeline. If the installation position is improper, the medium will not flow smoothly in the valve, generating vortices and pressure fluctuations, thereby affecting the sealing performance of the valve.
For example, when installing a ball valve on a horizontal pipeline, if the valve stem is installed upward, impurities in the medium may accumulate at the bottom of the valve core, affecting the closing of the valve.
- Poor pipeline alignment
When installing a ball valve, if the pipeline and the axis of the valve are not aligned, the valve will be subjected to additional stress, causing the valve body or valve core to deform and affecting the sealing effect. Poor pipeline alignment may be caused by pipeline installation errors, unreasonable bracket settings, etc.
- Untimely maintenance
Ball valves need to be regularly maintained during use, including cleaning the sealing surface, checking the wear of parts, and replacing aging seals. If maintenance is not timely, impurities will accumulate inside the valve and parts will wear out, which will reduce the sealing performance. For example, if the sealing surface is not cleaned for a long time, impurities will form abrasives between the sealing surfaces, further increasing the wear.
- Improper operation
When the operator opens and closes the ball valve, if the operator uses too much force, rotates too fast or does not fully reach the position, it will damage the valve and affect the sealing performance. For example, when the manual ball valve is closed, if the operator forcibly rotates the valve stem, it may cause the valve stem to deform or the sealing ring to damage.