The sphere has leaked. Under the normal operating pressure of the equipment, there was excessive leakage between the valve disc and the sealing surface of the valve seat. The reasons for this are as follows: five points. 

1. Dirt has fallen onto the sealing surface. To solve this problem, use an extension wrench to open and close the valve several times to flush away the dirt. 

2. Damage to the sealing surface. Depending on the extent of the damage, the method of turning followed by grinding is adopted for repair. After the repair, the sealing surface should be smooth, and its roughness should be kept below Ra = 0.2 μm. 

3. Due to improper assembly or excessive load on the pipeline, the concentricity of the parts has been compromised. The assembly should be redone or the additional load on the pipeline should be removed. 

4. The opening pressure of the valve is too close to the normal operating pressure of the equipment, resulting in the sealing surface being too low compared to the pressure. When the valve is subjected to vibrations or pressure fluctuations of the medium, leakage is more likely to occur. The opening pressure should be appropriately adjusted according to the strength conditions of the equipment. 

5. The spring becomes loose, thereby reducing the set pressure and causing the valve to leak. This may be caused by high temperatures or corrosion, etc. Measures such as replacing the spring or even the valve (if it is due to improper selection) should be taken based on the cause. If it is merely caused by improper adjustment, then simply tighten the adjustment screw appropriately.