Guangzhou Casselin Trading Co., Ltd. , https://www.casselinautoparts.com
Discussion on Valve Problems and Selection in Water Supply Network
In a municipal water supply network, valves play a critical role in ensuring the safe and efficient distribution of potable water to millions of households. These networks span hundreds or even thousands of kilometers, covering every corner of the city. Due to the essential nature of water for human survival, maintaining the integrity and reliability of the water supply system is of utmost importance. However, aging infrastructure, environmental factors, and operational demands often lead to pipe failures, necessitating regular maintenance, repairs, and replacements. As a result, localized water shutdowns are inevitable. To minimize the impact of such disruptions, control valves must be strategically installed throughout the network.
Valves act as "preventive" tools in the water supply system, typically kept open to ensure continuous flow. But when needed, they must close quickly and reliably to isolate faulty sections. The performance of these valves is influenced by various factors, including valve selection, manufacturing quality, installation, operation, and maintenance. Among these, the quality of the valve itself is the most crucial determinant of its reliability.
A survey conducted among 20 water supply companies and inspections of ten valve manufacturers revealed that valves in the water supply network are numerous, widely distributed, and often prone to issues. Their operation is infrequent, and they remain in standby for long periods. When called upon, they may not function properly, which highlights the need for careful consideration during their selection, production, testing, assembly, and management.
**Valve Selection**
1. **Gate Valves vs. Butterfly Valves**
In the water supply network, larger pipes often use butterfly valves to reduce the depth of burial and minimize soil impact. However, gate valves are preferred for smaller diameters. The choice between the two should be based on specific conditions. Over the past decade, butterfly valves have shown higher failure rates compared to gate valves, suggesting that increasing the use of gate valves could be beneficial, provided technical and financial constraints allow it.
2. **Soft-Seal Gate Valves**
In recent years, domestic manufacturers have developed soft-seal gate valves, which offer several advantages over traditional wedge or parallel double gate valves. These include:
- Precision casting of the valve body and cover, reducing machining needs and eliminating the use of copper rings.
- Reduced risk of slag accumulation, leading to fewer operational failures.
- Uniform and interchangeable rubber-lined valve plates.
Soft-seal gate valves are increasingly favored in the water industry. However, China’s domestic production still faces challenges. Some manufacturers use imported components, such as soft-seal valve plates from foreign suppliers. For instance, one Shanghai-based company uses resin sand mold casting for the valve body and imports the lining rubber. Others embed copper nut blocks into the rubber valve plate, which can cause wear and tear. A foreign manufacturer, however, integrates the copper block directly into the rubber, improving durability but requiring high concentricity in the valve cover and body. Proper operation is also important—valves should not be fully closed unless necessary, to avoid damage to the rubber seal.
3. **Butterfly Valves**
Several issues arise with the selection of butterfly valves. Midline butterfly valves are commonly used in small-diameter applications and perform well. Two main manufacturing methods exist: one with a support frame (e.g., Tanggu products) and another without (e.g., Zhengzhou products). The latter provides a larger flow area but raises concerns about longevity. However, field surveys suggest that this is not necessarily the case. Despite differences in design, both types have proven effective in practice.