To prevent the valve cavitation damage to determine the valve cavitation damage three methods
This article provides a comparative analysis of three main methods used to diagnose cavitation damage in control valves. It emphasizes the importance of understanding and applying the laws governing fluid dynamics, as well as controlling the outlet flow rate to minimize or prevent valve damage during selection. Control valves play a crucial role in the fluid industry, and with growing demands for energy efficiency, stable operation, reduced spare parts, and quick after-sales support, users are increasingly focused on optimizing, selecting, and using these valves effectively. This is because control valves act as actuators in systems and directly influence the operational status of the entire device. According to statistics, up to 65% of system shutdowns are attributed to control valve failures, and the quality of the selected valve significantly impacts product quality and yield.
Over the past five years, there has been rapid development in control valve technology. Leading manufacturers have introduced specialized valves capable of operating under extreme conditions such as high temperature, high pressure, cavitation, flashing, abrasive media, and high-noise environments. At the same time, intelligent diagnostic positioners have emerged, enabling real-time monitoring of valve performance and providing maintenance alerts to optimize valve usage. These advancements have greatly improved system stability and reduced weak points in operations.
However, the key challenge remains: how can we accurately calculate and select the right valve? Experience shows that in harsh conditions, cavitation often leads to severe damage, accompanied by noise, internal vibrations, and flow blockage. Proper valve calculation and selection are essential to reduce or avoid cavitation. Currently, different manufacturers use various methods to evaluate cavitation. This paper primarily discusses the KE method, δ method, and XFz method, analyzing how they help in reducing cavitation and ensuring correct valve selection.
Cavitation in control valves occurs when the fluid passes through the valve’s constricted area, causing a drop in pressure. If the pressure falls below the medium's saturation vapor pressure, liquid vaporizes, forming gas bubbles. As the fluid moves to the expansion section, the pressure rises again, causing the bubbles to collapse. This process, known as cavitation, generates high-energy jets and shock waves. Experiments have shown that a bubble with a diameter of 150 micrometers collapsing can produce a jet velocity of 400 km/h, creating an instantaneous pressure of several thousand kilograms, leading to severe erosion and wear on the valve components. It also causes intense vibration and noise, potentially blocking the flow.
Severe cavitation can rapidly damage the valve trim or alter its operational characteristics. Experimental studies using water have confirmed the cavitation process from a microscopic perspective. A mathematical model describing the bubble pressure balance is used: Pg + Pv = 2α/R + P, where Pg is the pressure inside the bubble, Pv is the medium's saturated vapor pressure, α is a constant, R is the bubble radius, and P is the ambient pressure. The equation highlights that changes in flow conditions, especially from steady to turbulent, significantly affect surface tension and bubble behavior. The radius R reflects the bubble's expansion before collapse, and under certain temperature and pressure conditions, the external pressure and vapor pressure are the main factors driving cavitation.
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