**I. Overview**
With the rapid development of China's infrastructure and large-scale national projects, the demand for valves in industries such as power, petroleum, chemicals, and municipal water supply and drainage systems has significantly increased. Among these, butterfly valves have become widely used due to their efficiency and cost-effectiveness. In China, metal hard-seal butterfly valves are mainly categorized into two types based on their sealing structure: elastic hard-seal and multi-layer hard-seal. The former is typically produced in sizes below DN500, while larger diameters mostly use the multi-layer structure. Due to the high volume of small-diameter butterfly valves in use, users often encounter various issues during installation and operation. This article aims to summarize common problems and provide guidance on correct installation and usage.
**II. Analysis of the Elastic Structure and Common Issues**
Elastic hard-seal butterfly valves consist of key components such as the valve body, disc, stem, elastic seat, and pressure ring. The pressure ring plays a critical role in the sealing process. It serves as the sealing surface between the valve body and the pipe flange, and its side features bolt holes that secure the valve seat and connect the valve body. However, the presence of these bolt holes reduces the effective sealing diameter. Many users employ flat flanges with an internal passage that is 10–20 mm smaller than the nominal size. This mismatch can cause misalignment, leading to leakage at the bolt holes when the valve is installed incorrectly. The leakage typically occurs from the backside of the pressure ring, which can compromise the system’s integrity.
**III. Special Flanges**
Currently, there is no specific standard in China for elastic hard-seal butterfly valves. According to existing national standards, flanges are usually socket-type, with inner diameters matching the nominal bore to ensure a larger effective sealing area and easier installation. Users should be aware that when using elastic hard-seal butterfly valves, it is essential to pair them with special flanges—especially those that match the pressure ring surface of the valve body. Using non-specialized flanges may lead to improper sealing and potential leaks.
**IV. Direction of the Arrow on the Valve Body**
The arrow on the valve body typically indicates the direction of the medium flow. Most users install the valve according to this direction, which is generally acceptable. However, for eccentric butterfly valves, this approach may not always work. For example, if the valve is installed in the same direction as the flow, and the pressure on the inlet side drops or becomes zero, the fluid may flow backward. If the outlet pressure is higher, the valve may experience reverse pressure, which can affect its sealing performance and lead to leaks. Therefore, the arrow on the valve body actually represents the direction of the medium pressure, not just the flow direction. Before installation, users should understand the pressure direction after the valve is closed and align the arrow accordingly to ensure proper sealing and long-term performance.
**V. Acceptance and Inspection for Elastic Hard-Seat Butterfly Valves**
It is crucial for users to conduct thorough inspections when purchasing butterfly valves. This includes checking the product quality and ensuring the valve functions properly after installation. However, many users overlook testing the hard-seal butterfly valve during sampling, which can lead to doubts about the product’s quality or even rejection. One reason for this issue is the design of the pressure ring bolts. These bolts (ranging from 4 to 12 in number, with a maximum diameter of M10) are primarily used to fix the elastic seat and cannot withstand full medium pressure. When installed on the outer flange, the full pressure is applied, which can cause discrepancies during testing and result in false leakage reports.
During testing, the pressure ring should be placed upward, and a pressure plate matching the flange size should be used. If a tester is employed, the pressure claw should be evenly pressed onto the plate. For blind plate testing, the two-piece flange-clamp method is commonly used. Some flange-type valves come with pre-installed flanges for user convenience, but the pressure ring bolts still bear the full medium pressure, which they are not designed to handle. Therefore, using a blind plate ensures more accurate test results and better alignment with real-world conditions.
Understanding the structure and function of the elastic hard-seal butterfly valve can greatly improve installation efficiency and ensure correct usage.
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