Structural and functional requirements of manhole covers
1. The manhole cover should be equipped with a filling port and an emergency release device
2. The filling port should be fully openable and equipped with a secondary opening device
3. The manhole cover should have a spare interface for installing oil and gas recovery valves, anti-flooding sensors, breathing valves and other valves
4. The emergency release device should be designed to prevent liquid accumulation and ice formation
5. When closed, keep the manhole cover in a sealed state to prevent liquid or gas from flowing out of the tank
6. When the pressure in the tank is lower than the release pressure, return to the closed state