Through the analysis of the structural principle of the fixed pipeline ball valve, found that the sealing principle is the same, using the “piston effect” principle, and only the sealing structure is different.
Valve in the application of the problem is mainly manifested in different degrees, different forms of leakage, according to the principle of sealing structure and installation and construction quality analysis, the causes of valve leakage are the following aspects.
1. Valve installation and construction quality is the main reason
In the installation construction does not pay attention to the valve sealing surface and sealing seat ring protection, sealing surface damage; installation is completed, the pipeline and valve cavity blowing is not complete, not clean, in operation there are welding slag or gravel stuck between the ball and sealing seat ring, resulting in sealing failure. In this case, in an emergency, the upstream sealing surface should be temporarily injected with the appropriate amount of sealant to alleviate the leakage, but can not completely solve the problem, if necessary, the valve sealing surface and sealing seat ring should be replaced.
2. Valve mechanical processing, sealing ring material, and assembly quality reasons
Although the valve structure is simple, it is a high demand for mechanical processing quality products, its processing quality directly affects the sealing performance. Seal seat ring and ring seat assembly clearance and each ring surface area to be calculated accurately, the surface roughness to be appropriate. In addition, the selection of soft seal material is also very important, not only to consider corrosion and wear resistance but also to consider its elasticity and stiffness. If it is too soft, it will affect the self-cleaning ability; if it is too hard, it will be easy to fracture.
3. Reasonable selection according to the application and working conditions
Different sealing performances and sealing structures of the valve using different occasions, only different occasions to choose a different valve, to obtain the ideal application effect. In the case of the West-East gas pipeline, for example, fixed pipeline ball valves with bi-directional sealing should be selected as far as possible (except for orbital ball valves with forced sealing, which are more expensive). This way, if the upstream seal is damaged, the downstream seal can still function. A forcibly sealed track ball valve should be selected if absolute reliability is required.
4. For valves with different sealing configurations, different methods of operation, maintenance, and servicing should be applied
For valves that do not have leaks, the valve can be filled with some grease before and after each operation or every 6 months in small amounts at the stem and sealant injection ports, and only in cases where leaks have occurred or cannot be completely sealed is the appropriate amount of sealant injected. Because of the high viscosity of the sealant, if the valve is not normally filled with sealant, it will affect the self-cleaning effect of the spherical surface, often counterproductive, bringing some small grit and other dirt between the seal to cause leakage. For valves with a two-way seal, if the site safety conditions permit, the pressure in the valve cavity should be released to zero, to ensure sealing.
Post time: Feb-23-2023