A valve may be leak-tight at its seat but exhibit external leakage from the stem or packing. This problem occurs more frequently in valves that operate often or have aged.
Where the leak occurs
The leak is located around the stem, the bonnet, or the valve sealing point. It may be very small and not easily visible.
Possible causes
Packing wear, loose sealing, stem corrosion, or misalignment can lead to a loss of seal integrity.
Inspection
An appropriate gas detector or approved foaming liquid is used. The inspection is also performed with the valve in different positions, where applicable.
Restoration
Maintenance is performed according to the manufacturer's instructions. No arbitrary tightening or intervention on a pressurized valve is permitted.