If the valve is not strict, first of all should find out where the problem appears, and then according to the corresponding method to deal with, the general valve is not strictly closed for the following reasons:
(1) Impurities are stuck in the sealing surface, debris deposition at the bottom of the valve or cushion between the disc and the seat;
(2) Stem thread rust, valve can not rotate;
(3) Valve sealing surface is damaged, resulting in leakage of media;
(4) Stem and disc connection is not good, so that the disc and seat deflection can not be closely contacted.