Gas pressure regulating valve natural gas special valve classification and how to choose
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**The Current Situation of Gas Valves in China**
Before the 1980s, gas-specific valves did not exist; only water valves were used. Since the reform and opening up, the rapid development of economic construction has driven the growth of the gas industry. Valve manufacturers began to focus on developing gas-specific valves. At that time, they mainly dealt with impurities in coal-based gas, such as tar and aromatic compounds. These substances could form a "gas glue" when mixed with dust, causing issues like valve sealing failure or stem sticking. With the introduction and application of natural gas, the nature of the gas changed. Natural gas is cleaner and drier than coal gas, but it still contains sand and dust, and its pressure is higher (coal gas typically operates at 0.05–0.3 MPa, while natural gas can reach 0.4–1.6 MPa or even higher). The presence of dust creates a strong abrasive effect inside the valve. Under various gas conditions, choosing the right gas valve for urban areas, gate stations, storage equipment, and underground pipelines remains a critical challenge.
**Valves Installed on Underground Pipelines Must Meet Specific Requirements**
Valves installed in underground pipelines must have sufficient **strength** and **stiffness**. While strength refers to the maximum pressure the valve can withstand, stiffness ensures that the valve maintains its shape under external forces and retains reliable sealing performance. Key requirements include:
1. Minimizing the valve's structural height to reduce burial depth;
2. Equipping the valve top with a fully enclosed open/close indicator for easy operation monitoring;
3. Full-path design to reduce flow resistance, allowing passage of pipeline cleaners and detectors;
4. Reliable sealing: soft-seal valves must not allow any visible internal leakage at 1.1 times the nominal pressure, while hard-seal valves should have less than 0.3 DN mm³/s leakage;
5. Corrosion-resistant valve housing, with materials selected based on the medium and pressure;
6. Designing for minimal maintenance and long-term reliability to reduce road closures due to repairs;
7. Low torque and limited number of revolutions for manual operation, enabling quick shutdown during emergencies;
8. Direct-buried valves are recommended to avoid excavation of basement wells.
**Material Selection for Gas Valve Casings**
Choosing the appropriate material for the valve casing depends on the pipeline's operating pressure. The goal is to ensure safe operation while optimizing cost and utility. For example:
- Medium-pressure B-class (0.2 MPa) pipelines recommend gray cast iron valves for their corrosion resistance and low cost;
- For pressures up to 0.4 MPa or below 0.8 MPa, ductile iron or cast steel is preferred, with ductile iron offering better mechanical properties, corrosion resistance, and lower cost;
- High-pressure A-class (1.6 MPa and above) recommends cast steel valves;
- Recently, PE pipes have been introduced for low-pressure applications, with PE ball valves gaining popularity for direct burial and good sealing performance, though they remain expensive for larger sizes.
**Common Gas Valves Used in China’s Gas Industry**
Several types of gas valves are widely used in China, each with unique advantages and limitations:
1. **RX Series Oil-Sealed Plug Valve**: Developed using Japanese technology, it features a hard-seal structure to prevent "gas glue" buildup. However, it has high flow resistance, requires grease, and is difficult to manufacture in large diameters.
2. **RZ Series Parallel Gate Valve**: Designed for large-diameter pipelines, this valve effectively removes "gas glue" and includes features like drain holes and full-diameter design. It is commonly used in medium-pressure systems.
3. **RQZ Series Ductile Iron Gate Valve**: Improved for natural gas applications, it offers enhanced wear resistance and higher pressure ratings.
4. **Butterfly Valve**: Light and low-cost, but with poor sealing and flow resistance, making it unsuitable for most gas pipelines except special cases.
5. **Slab Gate Valve**: Offers low flow resistance and is suitable for small-diameter, low-pressure systems, but lacks clear indication of closed/open status.
6. **TRZ Series Elastic Sealing Gate Valve**: Features elastic sealing seats that compensate for wear, making it ideal for high-pressure systems. It allows for direct burial and has excellent sealing performance.
7. **RQ Series Ball Valve**: Widely used for its compact design and good sealing. Fixed-ball versions are preferred for large diameters and high pressure.
**Special Purpose Gas Valves**
1. **Emergency Shut-Off Valve for Pressure Regulators**: Designed to quickly shut off gas supply in case of overpressure or pressure loss, ensuring safety. It is integrated with filters and regulators.
2. **Gas Emergency Shut-Off Valve**: Activated by automatic monitoring systems, it cuts off the gas source during leaks or disasters. Electric ball valves are preferred for fast response and reliability.
3. **Gas Check Valve**: Prevents backflow in compressors and storage stations. The R-type series improves sealing and reduces noise.
**Standards for Gas Valves**
China has established several key standards for gas valves, including CJ3005-1992, CJ3055-1995, and others. These standards regulate the industry, promote technological advancement, and ensure safety. They are widely accepted by gas companies and valve manufacturers.
**Recommendations for Valve Selection**
Based on current conditions and needs, the following recommendations are made:
1. For medium-pressure B systems, use direct-buried RZ series gray cast iron parallel gate valves;
2. For medium-pressure A systems, choose RZ, RQZ, or TRZ series valves;
3. For high-pressure B or A systems, use TRZ series or fixed-ball ball valves;
4. For high-pressure A and above, opt for fixed-ball ball valves;
5. In storage stations or ground equipment, use gate valves for larger diameters and lower costs;
6. In pressure regulator systems, use RZ or RQZ parallel gate valves or floating ball valves;
7. In pressure regulating boxes, if butterfly valves are necessary, choose multi-eccentric high-quality models with Teflon or hard seals.
With the continued expansion of natural gas infrastructure and the introduction of new sources like the West-East Gas Pipeline and Russian gas, the demand for advanced gas valves will grow. This will drive innovation and the development of more efficient and safer solutions for the gas industry. (Source: Hebei Zhenxing Gas Pressure Regulator Co., Ltd.)
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