How to determine whether the valve is internal leakage or external leakage?

In the daily use of the valve, often encounter a variety of faults, valve leakage is one of the most common faults, and valve leakage generally have two cases of internal leakage and external leakage! So, the difference between the two is what?

Valve internal leakage, generally refers to when the valve is completely closed, there are still medium from the valve flow path outlet outlet, leakage or drip, etc., popular point, that is not tight, sealing is not good! The reason of the failure, usually due to medium erosion, which contains impurities and other reasons. Even if the valve screw (stem) tightened in place, because there is still a gap between the spool and the valve, the media can also flow past.

Valve leakage, generally refers to when the valve is completely closed or open, the valve packing of the external sealing parts, the emergence of medium leakage. The valve is connected with the flange or threaded connection between the sealing medium resulting in outflow connection sealing surface, or the stem and Glenn (i.e. stem disc root leakage between the sealing gland) lead to the media, or on the body blank caused by trachoma leakage, as well as for medium erosion resulting in body wear the leakage.