Difference Between Internal and External Leakage of Valves

In the daily use of valves, various failures often occur. The leakage of valves is the most common one among many failures and it generally includes internal leakage and external leakage. So, what is the difference between the two?

The internal leakage of the valve usually refers to the condition that the medium still leaks from the passageway of the valve when the valve is completely closed. Generally speaking, the internal leakage means that the valve is not tightly closed and the seal is not good. This failure is usually caused by erosion and wear of media. Even if the valve lead screw (the valve stem) is screwed, the medium can still flow through the valve passage because there is still a gap between the valve core and the valve body.

Generally, the external leakage of the valve is that the leakage of the medium occurs in the external seal element of valve packing after the valve is fully opened or closed. The medium leakage is caused by the poor seal between the valve and the connecting flange or connecting thread, the poor seal between the valve stem and the packing gland, sand holes on the valve body blank, or the wear of the valve body due to the medium erosion.