(1) Thread damage due to excessive operation;
(2) lack of lubrication or lubricant failure;
(3) Stem bending and torsion;
(4) The surface finish is not good;
(5) Cooperative public service is forbidden and bites too tightly;
(6) The stem nut is skewed;
(7) Improper selection of information, for example, the valve stem and the valve stem nut are the same raw material, which is easy to bite;
(8) The thread is corroded by the medium (refers to the valve with the dark rod valve or the stem nut in the lower part);
(9) The open-air valve lacks maintenance, and the valve stem thread is covered with dust and sand, or is corroded by rain, dew, frost and snow.
Ways to prevent it:
(1) Operate carefully, do not make it violent, do not go to the top dead center when opening, and turn the handwheel one or two times after opening enough, so that the upper side of the thread is sealed, so as to avoid the medium pushing the valve stem upward;
(2) Check the lubrication status frequently and adhere to the normal lubrication condition;
(3) Do not use a long lever to open and close the valve, workers who are accustomed to using a short lever should strictly control the force and proportion, in order to prevent twisting and bending the valve stem (refers to the valve where the handwheel and the valve stem are directly connected);
(4) Improve the quality of processing or repair to meet the standard requirements;
(5) The data should be corrosion-resistant, adapt to the working temperature and other working conditions;
(6) Do not use the same raw material as the valve stem nut;
(7) When using plastic as the stem nut, the strength should be checked, not only the good corrosion resistance and small friction coefficient should be considered, but also the strength should be considered.
(8) The open-air valve should be equipped with a valve stem maintenance sleeve;
(9) For normally open valves, turn the handwheel regularly to avoid rusting the valve stem.
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