There must be sufficient "strength" and "stiffness" — "strength" refers to the valve's ability to withstand the highest pressure of gas transported within the pipeline. More importantly, it must have enough "stiffness," meaning that under various external forces affecting the underground network, the valve can still maintain its shape and reliably ensure the sealing performance:
1. Full-bore design to reduce flow resistance, facilitating the passage of pipeline cleaning devices or pipeline detectors, and should also meet the requirements for non-stop transmission closed-hole drilling machines to drill holes in pipelines;
2. Minimize the structural height of the valve (the height from the centerline of the valve’s flow cross-section to the top of the valve) to reduce the burial depth of the pipe;
3. A fully enclosed open-close indicator should be installed on the top of the valve to help operators clearly understand the status of the valve at any time, which is an important condition for safe operation;
4. The design of the valve components should consider low-maintenance or maintenance-free structures to minimize the workload of inspections and maintenance, reducing road closures caused by valve maintenance and minimizing traffic disruptions;
5. Most underground pipeline valves are manually operated, requiring small opening and closing torques, with a limited number of full turns to quickly cut off the gas supply in case of an accident;
6. Urban roads often have crowded and complex underground pipelines, making it unsuitable to dig basement manholes; therefore, buried valves are recommended;
7. Reliable sealing performance: According to the CJ3055-95 standard "Testing and Inspection of Urban Gas Valves," soft-sealed valves must not have any detectable internal leakage under 1.1 times the nominal rated operating pressure, while hard-sealed valves are allowed an internal leakage rate of less than 0.3DNmm³/s under the same pressure. This requirement is relatively strict. For example, a 500mm nominal diameter gas valve cannot leak more than 9 milliliters per minute (a typical drinking cup holds 200 milliliters). External leakage is absolutely not allowed;
8. The housing of gas valves used in underground networks must be corrosion-resistant. It is recommended to select different housing materials based on the conveyed medium and usage pressure of the pipeline.