Reason：
1. High quality cast iron castings, valve body and valve cover blisters, loose organization, slag and other defects on the body
2. Cold cracking;
3. Bad welding, there is a slag, not welded, stress crack and other defects;
4. Cast iron valve damage after heavy impact.
Maintenance method:
1. To improve the quality of casting, the installation of the strict accordance with the provisions of the strength test;
2. The temperature at 0 degrees and 0 degrees below the valve, should be insulated or mixed heat, stop the use of the valve should be excluded from the water
3. Welding body and the valve cover shall be welded by the welding procedure, and the test and strength test shall be carried out after welding;
4. Valve prohibit push put a heavy load, not allowed to hand cast iron and non metal hammer hit the valve, large diameter of the valve installation should stand.
