How to eliminate valve cavitation?
How to eliminate valve cavitation? Valve with the passage of time, parts degradation, valve cavitation caused by the pipeline system prone to serious damage. Most of the damage is caused by vibration and noise energy, which accelerates the corrosion process. The formation and collapse of the condensation flow near and downstream of the bubble caused by the vibration of high noise level and large amplitude reflected by cavitation erosion. Although this usually occurs in ball valves and rotary valves in the valve body, it can actually occur in a short, high recovery v-ball valve similar to the wafer body, especially the piping on the downstream side of the butterfly valve. When the valve is stressed at a position, it is easy to produce cavitation phenomenon, which is easy to leak in the valve piping and welding repair, and the valve is not suitable for this section of pipeline.
Whether cavitation occurs inside or downstream of the valve, the equipment in the cavitation area will be widely damaged. Ultra thin film, spring and cantilever structure with small cross-section, large amplitude vibration can trigger oscillation fault. Frequent fault points are found in instruments such as pressure gauges, transmitters, thermowells, flow meters, and sampling systems. Actuators, positioners and limit switches containing springs will suffer accelerated wear, mounting brackets, fasteners and connectors will become loose and fail due to vibration.
Fretting corrosion, which occurs between worn surfaces exposed to vibration, is common near cavitation valves. This will produce hard oxides as abrasive wear between surfaces to accelerate wear. The equipment affected includes isolation and check valves, in addition to control valves, pumps, rotating screens, samplers and any other rotating or sliding mechanisms.
High amplitude vibration will also cause metal valve parts and pipe wall cracking and corrosion. Scattered metal particles or corrosive chemical materials may pollute the medium in the pipeline, which will have a significant impact on the sanitary valve pipeline and high-purity pipeline medium. This is not allowed.
The prediction of cavitation failure of plug valve is more complicated than simply calculating the pressure drop. It is possible that the pressure in the main stream drops to the point where the vapor pressure of the liquid is local vaporization and the vapor bubble collapses. Some valve manufacturers predict annual initial corrosion failure by defining an initial damage pressure drop. A valve manufacturer's starting method for predicting cavitation damage is based on the fact that vapor bubbles collapse, causing cavitation and noise. The manufacturer has determined that significant cavitation damage can be avoided if the calculated noise level is below the following limits.
