1, cast iron casting quality is not high, the valve body and the valve body with trachoma, loose tissue, slag and other defects 2, the day cold cracking; 3, poor welding, there is slag inclusions, welding, stress cracks and other defects 4 , Cast iron valve is hit by heavy objects after the damage to the exclusion method: 1, improve casting quality, strictly in accordance with the provisions of the pre-installation strength test; 2, the temperature of 0 ° and 0 ° below the valve should be incubated or mixed heat, stop using The valve should exclude water. 3, the weld consisting of the valve body and valve cover should be carried out according to the relevant welding procedures, after welding should be carried out testing and strength testing; 4, the valve is prohibited to push heavy objects, not allowed to use hand hammer impact on the cast iron And non-metallic valves, large-diameter valve should be installed bracket