Causes of Valve Leakage and Its Preventive Measures (Part Two)

1. Cause analysis of valve leakage

1.1 There are some quality problems for the valve itself.
The parts of the valve which are prone to cause quality problems are divided into two parts. One is the surface and the other is the inner part. Because the valve needs to control the fluid in the pipeline system, there are many sealed parts. Before installation, if there are quality problems on the exterior of the valve, such as surface scars, cracks, rust and flange deformation, etc., it is obvious to find, so it can be handled in time. However, its inherent quality problems are difficult to find, which is also the main cause of valve leakage, such as internal sand holes, slag inclusion, bubbles, welding defects, or improper material selection, unreasonable design, improper heat treatment, weak connection and so on. The existence of these problems will lead to premature damage or leakage of the valve under the action of fluid during use.

1.2 The erosion of internal medium causes the damage of sealing surface
When the valve is in use, its internal medium will flush and cavitate the sealing surface of the valve when flowing in the pipeline. Under the constant flushing and cavitation of the medium, the sealing surface of the valve is easy to be damaged locally. At the same time, combined with the chemical erosion, it comprehensively acts on the sealing surface, which leads to the valve being easily damaged under the erosion, causing leakage and even scrapping.

1.3 Damage caused by improper selection and manipulation
When selecting valves, they should be selected according to specific working conditions. If they are not properly selected, there may be loose sealing, resulting in internal leakage. At the same time, it is necessary to distinguish the differences and diverse functions between different valves, thus reducing erosion and wear on sealing surfaces. In addition, if the operation of the valve is not standardized during installation, and the quality control measures are ineffective during installation, it will also cause valve leakage. Sand, welding slag and metal scraps should be strictly prevented from entering the valve cavity during maintenance. Once these impurities enter the valve cavity, the sealing effect of the valve will be seriously affected.

1.4 There are problems in design and processing quality.
If the error is too large in the valve manufacturing process, the valve plate and valve seat are not concentric, and the sealing surfaces are not completely matched, resulting in leakage. However, the poor processing of sealing surface is mainly manifested in the defects such as cracks, air holes and ballast, which are caused by improper selection or operation of surfacing and heat treatment. Improper material selection or heat treatment will cause the hardness of sealing surface to be too high or too low, which will eventually lead to uneven hardness and corrosion resistance of sealing surface. The sealing surface materials of valve plate and valve seat do not meet the using requirements. The machining accuracy is not enough. The wedge angles of valve plate and valve seat of gate valve do not match. The sealing surface width is different and the coincidence degree is poor, all of which will cause the valve plate out of place, and the valve will not close.