Before delivery LIIXN made test for all the valves,and why it also have leakage?

We presume that:

1. When the valve is make pressure test, there will be force to cause the packing to expand, and after the test, the external force is lost, which may cause the bolt to be a little loose

2. The valve needs to be ultrasonically cleaned before leaving the factory, so that the dirt and oil on the surface of the valve can be removed, but when it is cleaned by ultrasonically, it will vibrate and cause the bolts to become loose.