In water supply, wastewater, and industrial water systems, valves are core components used to control fluid flow and isolate sections of the system. Their sealing performance directly affects operational safety and overall system stability.
In long-term service, water valves are subjected to frequent opening and closing, pressure fluctuations, and continuous exposure to the process medium. Once sealing performance begins to degrade, leakage is likely to occur. This not only interferes with normal operation but can also lead to resource loss and potential safety risks.
For these reasons, a systematic analysis of valve sealing performance and its failure mechanisms is of practical importance in engineering applications.
Common Sealing Materials and Sealing Technologies
Types of sealing materials
In general, sealing materials used in valves can be divided into two main categories: soft seals and metal (hard) seals.
Soft sealing materials—such as elastomers (EPDM, NBR) and PTFE—offer good elasticity and conformability, making them well suited for low-pressure and ambient-temperature applications. However, their resistance to high temperatures and aggressive media is limited, and they are more prone to aging or degradation under harsh operating conditions.
Hard sealing materials—such as stainless steel and ceramic—provide excellent resistance to high temperature and wear, and are typically used in high-pressure, high-temperature, or corrosive service. These materials, however, place higher demands on machining accuracy and assembly quality, and generally involve higher manufacturing costs.
Common Sealing Technologies
In terms of sealing technology, different sealing methods are typically applied to different structural areas of a valve.
- Packing seals are mainly used at the valve stem. By compressing the packing, sealing is maintained during valve operation, preventing the medium from leaking along the stem.
- O-ring seals feature a simple structure and easy installation. They are commonly used at static connection points, such as valve bodies or flange interfaces, to achieve reliable static sealing.
- Metal-to-metal seals rely on high strength and durability. They are generally applied in valves operating under more demanding conditions or where a long sealing service life is required.
Common Sealing Materials and Technologies
Category | Material / Technology | Key Characteristics | Typical Applications | Limitations |
Soft sealing materials | Rubber (EPDM, NBR) | Good elasticity and conformability | Water supply, drainage, and general industrial water systems | Limited high-temperature and corrosion resistance; prone to aging |
Excellent chemical stability; low friction coefficient | Corrosive water media, water treatment systems | Limited high-temperature capability | ||
Hard sealing materials | Stainless steel | High temperature and wear resistance | High-pressure and high-temperature applications | High machining accuracy required; higher cost |
Ceramic | Excellent wear and high-temperature resistance | High-pressure, abrasive service | Brittle material; demanding manufacturing requirements | |
Sealing technologies | Packing seal | Simple structure; effective dynamic sealing | Valve stem sealing | Subject to wear; requires periodic adjustment |
O-ring seal | Easy installation; reliable static sealing | Flange joints and fixed connections | Limited high-temperature resistance; susceptible to extrusion damage | |
Metal-to-metal seal | High strength and long service life | Valves with demanding service conditions or long sealing life requirements | High machining precision required; higher cost |
Types of Valve Sealing Failure
Valve sealing failure is a complex and varied phenomenon. In practice, it usually appears in two main forms: internal leakage and external leakage.
- Internal leakage
This occurs when the valve is in the closed position, but the medium continues to leak internally from the high-pressure side to the low-pressure side.
Typical causes: Internal leakage is commonly associated with wear, deformation, or poor contact of the sealing surfaces. During long-term operation, repeated contact between the disc (or gate) and the seat can lead to wear or surface damage, gradually reducing sealing performance.
- External leakage
This refers to leakage of the medium to the surrounding environment, most often occurring at the valve stem packing or flange connections.
Typical causes: Aging of packing materials can reduce elasticity, while loose bolts may cause uneven compression at flange sealing surfaces, ultimately resulting in leakage.
Differences in Failure Development
From the way sealing failures develop, valve sealing failures can generally be classified into sudden failures and progressive failures.
Sudden failure occurs abruptly. Typical examples include sealing surfaces being scratched by foreign debris during installation, or unexpected leakage caused by manufacturing defects. This type of failure is usually linked to inadequate quality control or improper execution of installation procedures.
Progressive failure, on the other hand, develops gradually during long-term operation. Common causes include aging of sealing materials and fatigue-related damage. This type of failure is closely associated with operating conditions, service environment, and the level of maintenance and management applied throughout the valve’s service life.
Main Causes of Valve Sealing Failure
Design-related factors
Sealing problems often begin at the design stage when actual operating conditions are not fully considered. In such cases, the sealing surfaces may not make proper contact when the valve is closed. This issue is especially evident in high-pressure or high-temperature applications, where material deformation or thermal expansion can further reduce sealing effectiveness and eventually lead to leakage.
Another common factor is an inappropriate match between sealing materials and the service medium. When materials are not well suited to the operating environment, aging, deformation, or performance degradation can occur during service, increasing the risk of sealing failure over time.
Manufacturing-related factors
Manufacturing quality has a direct impact on sealing reliability. If machining accuracy is insufficient, sealing surfaces may fail to achieve the required flatness or surface finish. Even minor deviations can create leakage paths once the valve is placed in service.
Material quality control is equally critical. Internal defects such as porosity or inclusions from the casting process, as well as raw materials that do not meet specified composition requirements, can weaken sealing components and reduce their corrosion resistance.
In addition, inadequate control of heat treatment and surface finishing processes—such as polishing or coating—can affect wear resistance and long-term stability, increasing the likelihood of sealing failure during operation.
Installation-related factors
Sealing failures caused by improper installation are most commonly associated with connection points. During flange installation, uneven bolt tightening can lead to non-uniform contact pressure on the sealing surfaces. As a result, the gasket may not seat properly, increasing the risk of external leakage.
Installation conditions and handling details also play an important role. Low temperatures, humid environments, or residual debris inside the pipeline can damage sealing surfaces and compromise initial sealing performance.
Operation and maintenance-related factors
During long-term operation, water composition, residual disinfectants, and other corrosive factors can gradually degrade sealing materials. For soft seals in particular, extended service may lead to hardening, cracking, or loss of elasticity, all of which reduce sealing effectiveness over time.
In addition, repeated temperature and pressure fluctuations, along with fluid erosion and particle-induced wear, can accelerate wear and aging of sealing surfaces.
How to Reduce Valve Sealing Failure
Reducing valve sealing failure requires attention at multiple stages, including design, manufacturing, installation, and operation and maintenance.
1. At the design stage, sealing structures and materials should be selected appropriately, with full consideration of actual operating conditions.
2. At the manufacturing stage, machining accuracy and material quality must be strictly controlled to ensure that sealing surfaces meet design requirements.
3. At the installation stage, standardized procedures should be followed to ensure uniform loading at connection points and clean sealing surfaces.
4. At the operation and maintenance stage, sealing conditions should be inspected regularly so that aging or wear can be identified and addressed in a timely manner.
During valve manufacturing and inspection, pressure testing and ammonia leak testing are commonly used methods to verify sealing performance. Pressure testing is used to determine whether leakage occurs under rated pressure, while ammonia testing is effective in detecting very small leaks.
When used together, these methods provide a more comprehensive evaluation of sealing performance under actual assembly conditions.
An analysis of sealing materials and failure mechanisms shows that sealing reliability depends on the combined control of design, manufacturing, installation, and service conditions.
At TFW Valve, we focus on the design and manufacturing of water valves. From sealing structure and material selection to final inspection, every step is optimized based on real operating conditions. Our goal is to provide water-system valves that offer greater durability, stable performance, and a lower risk of leakage in long-term service.
If you have any further questions, please contact us.
