Under what circumstances is the seal opened and closed? How to use it?

For example, the inlet and outlet valves of a safety valve must be sealed with lead seals; it is strictly prohibited to close them in such a way as to render the safety valve unusable. When servicing the safety valve, remove the lead seal and shut it down for maintenance. The purpose of a lead seal is to prevent personnel on site from making accidental operations, such as closing or opening valves that should not be closed or opened. It can lead to safety accidents or an unsafe condition.

The lead seal must be removed when the system is in normal operation; it shall not be closed. The valve can be closed only during maintenance of the safety valve under special circumstances, and once the lead seal is closed, it must not be opened again. This is merely a safety measure in critical locations to prevent accidental operations; standards specify certain such measures, such as safety valves. According to HGT-20570.2-1995, Section 12.0.1, cut-off valves are generally not installed on inlet pipes; if they must be installed, they should be sealed with lead so as not to interfere with the operation of the safety valves. The main settings are located in areas that have a significant impact on safety; controls are installed there because operating them involves high risks. As for the specific usage you mentioned, you can think of it this way: for safety measures in highly dangerous process areas, isolation is necessary, so the front valve must be opened; whereas in cases where it’s possible to bypass such safety measures, they must be sealed off with lead seals