How to prevent cavitation in the internal components of control valves
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In the fluid flowing through a control valve, two phenomena occur: flashing and cavitation. The occurrence of these phenomena not only affects the selection and calculation of the valve diameter, but also leads to severe noise, vibration, and damage to the components inside the valve, **reducing its service life. Flash evaporation: As the fluid passes through the valve components, its cross-sectional area decreases, causing the flow velocity to increase and the pressure to drop. When this pressure falls below the saturated vapor pressure at that temperature, bubbles form and escape – this phenomenon is known as \"flash evaporation\". Cavitation: When the pressure behind the fluid increases, these bubbles are crushed, resulting in what is called \"cavitation\". These two phenomena combined constitute \"cavitation erosion\" of the valve components, which can cause significant damage. The defects caused by flash evaporation are relatively smooth, whereas cavitation results in deep pits with a pitted surface. Media and situations where cavitation tends to occur: 1. Boiler feedwater 2. Desuperheated water 3. Steam condensate. Applications involving the regulation of fluid flow at high temperatures and pressures. Common methods to prevent cavitation: 1. Surface hardening of valve components: Used in cases with advanced manufacturing techniques, such as Messer’s single-seat valves with Stellite alloy cladding ； 2. Multi-stage pressure reducing valve: when the medium is relatively clean ； 3. General cage valves ； 4. Install a flow-limiting orifice plate: upstream or downstream ； For applications with low flow rates: 5. Install the valve at the lowest point of the system to increase the inlet and outlet pressures. 2023.9.4
How the internal components of control valves prevent cavitation is an important issue. Cavitation refers to the flashing and cavitation phenomena that occur in the liquid flowing through the control valve; this can lead to noise, vibration, and damage to internal components, thereby reducing the service life of the control valve. To prevent cavitation, the following methods can be adopted: 1. Surface hardening of valve components: The surface of valve components is hardened through processes such as alloy surfacing to enhance their resistance to cavitation. 2. Use multi-stage pressure reducing valves: When the medium is relatively clean, multi-stage pressure reducing valves can be used to reduce pressure and minimize the occurrence of cavitation. 3. Use cage valves: The structure of cage valves can reduce the occurrence of cavitation by lowering the flow velocity and thus reducing the pressure gradient. 4. Install flow-limiting orifice plates: Installing such orifice plates upstream or downstream can reduce the flow velocity, alleviate pressure changes, and decrease the risk of cavitation. 5. Install the valve at the lowest position of the device: Installing the valve at the lowest point of the device can increase the inlet and outlet pressures, thereby reducing the occurrence of cavitation. The above methods can be selected and used according to actual conditions in order to improve the cavitation resistance of control valves and extend their service life. .
The valve core is sprayed or welded with cemented carbide; a cage-type valve core is used!