Why work under the regulator should be avoided in the small open?

Control valve is automatic process control production process industry factory terminal control components. Control valve to adjust the stand or fall of quality, will directly affect the quality factory automatic process control. Therefore, to ensure that the regulator is stable and reliable work, for the process industry automation system, is very important. In practice, small open degree is one of the main cause of shorten valve life. So, why are small open degree of impact valve life? We followed kaidi instrument equipment factory to know the details the influence of the small open degree first cause erosion. Small open degrees to port clearance is too small, the medium flow rate is too large, regulating valve valve core, the seat is very severe, scouring will make the life of the valve exponentially decline, even in the short term can make the regulator of scrapped. Second, the small open degree lead to intense pressure, flow rate changes. When more than valve stiffness, cause the regulator to produce volatility. Third, the flow state of the work of the regulator, will be closed and the start jumping phenomenon, the regulator is not normal in the opening of adjustment. Valve opening if at about 3%, the valve core sealing surface throttling mouth too close, for the sealing face of valve core damage is very large. Fourth, some kinds of valve is not suitable for small open degree of work. Such as butterfly valves, unbalanced torque when small open degree, will produce jump on, jump off phenomenon. Such as pneumatic diaphragm regulating valves again if it is direct two-seater regulator, because this type of valve has two valve core seat, a valve core is in a state of flow open at ordinary times, another valve core in the flow closed state, although the valve for leakage is relaxed, but when the valve is in small scale, the valve becomes very poor stability, and prone to shocks. In short, if the regulator can work normally, not often wash, improve the service life of the valve, regulating valve should be avoided in small open work. Scale according to the practical experience, the valve is usually at least should be greater than 8% ~ 12%, but for the high pressure valve, two-seater valve, butterfly valve, regulating valve in flow close state, should be greater than 20% ( Linear valve) ~ 30% ( Logarithmic valve) 。 Small open degree of flash steam corrosion caused by flash and cavitation is caused by blocking the flow, when the fluid medium flow control valve seat, the minimum flow in reducing. When the fluid flows through reducing working medium, a beam thinner contraction. The minimum cross-sectional flow beam in actual reducing downstream, rather than reducing. Contracted flow section in place, the flow rate of the fluid medium, the largest velocity increases with the flow section of pressure greatly reduced, with fluid medium in the downstream extension beam, speed drop, pressure increases. When contracted flow cross-section of the fluid pressure is lower than the temperature of fluid saturated vapor pressure, flow will produce bubbles, beam forming gas liquid two phase flow. If in the cross section of the fluid in the contraction flow downstream, also is the outlet pressure of the valve is still lower than the temperature of fluid saturated steam pressure, steam bubble will be the production of large Numbers of downstream of the valve, it caused the phenomenon of flash. The discharge pressure is lower, the bubble, the greater the flash phenomenon is more serious. If the downstream pressure to return to the temperature of fluid saturated vapor pressure above, or inward explosion bubble will burst, causing cavitation. Steam bubble burst release energy, produce a similar to the noise of the sand flow through the valve. When the control valve in a small open degree, will feel the fluid through the noise, the body vibration will also strengthen, this is the cavitation happened. Flash condition compared with the working condition of cavitation, flashing mode of the gas liquid two phase flow will shrink after flow at the downstream of valve are present, than the effect of gas liquid two phase flow cavitation conditions time is long, the damage to the valve and pipe. The harm of flash flash the harm of main mechanical wear and corrosion. Carry the droplets on the one hand, bubble, the contact area through the valve body, has the strong impact effect on the interface, and because of the high gas velocity, the interface with Angle of impact, making contact with the bubble of body internal erosion is serious; The contact area on the other hand, when the body and fluid mechanical wear occurs, would undermine the original after treatment of the surface of the metal, and because some process medium mostly for water, containing oxygen, the metal surface to form a new oxide, metal surface corrosion phenomenon. Flash erosion damage is characterized by flushing the surface has smooth polished appearance. Scour the worst place generally in the velocity of the top, usually located on the valve core and valve seat contact online or nearby, so the body piece must also choose good erosion resistance. Cavitation of the cavitation of the hazards are mainly the impact of the rapid burst the bubble, and rupture form when the tremendous impact of the high-speed jet produces strong erosion effect on metal surface. If the bubble near the valve inside the solid surface rupture, the energy released will slowly tearing material, on the surface of the valve core is similar to the coal cinder rough surface. If the bubble burst in the downstream piping, can produce similar damage to the downstream piping. Response to solve the problem of small open degrees regulator to work with a variety of methods, probably has the following several kinds of common. Reduce the pressure difference on both ends according to the flow equation, the differential pressure reduction after hours, the traffic also decreases accordingly, to maintain the valve flow rate unchanged, will increase the valve opening. Therefore, you can process and regulating valve in the pipeline in series of manual valve, close to the regulator to the job opening, or after the regulator to increase current limiting orifice consumption part of the pressure drop.