When a hard sealed gate valve leaks, it is usually necessary to:
Confirm the leakage location: Is it inside the valve body (internal leakage, medium flowing out from the outlet end), at the flange connection, at the valve stem packing (external leakage), or is there a sand hole crack in the valve body?
Check operation: Is the valve fully closed in place? Is the operating torque appropriate?
Consider operating conditions: Is there any impurity or corrosiveness in the medium? Are the temperature and pressure within the valve design range? Have there been any drastic changes in temperature and pressure recently?
Check installation: Is the pipeline aligned properly? Is the pipeline support sufficient? Is the valve installed vertically?
Considering maintenance history: Has the valve been repaired recently? Has the packing been compressed or replaced?
Disassembly and inspection (if necessary): For internal leaks, it is usually necessary to remove the valve from the pipeline, disassemble and inspect the sealing surface of the gate and valve seat (scratches, wear, corrosion, deformation, impurity blockage), as well as the wear of the valve stem and valve stem nut.