Usually PN ≥ 16MPa valve is called high-pressure valve. The main problem in the use of high-pressure valves is the life-span problem (cavitation, flashing, erosion and other physical phenomena on the valve parts under large pressure drop). General structure of the valve in high pressure conditions can only be used for 1 to 2 months, in order to solve the problem of short life of high pressure valve, domestic and foreign manufacturers have made great efforts, respectively, in the material and structure to do a lot of exploration , Formed a wide range of products, mainly multi-stage high-pressure valve, labyrinth high-pressure valve and single-seat sleeve load-type high-pressure valve. Its purpose is only one, by reducing cavitation, erosion, flash and other physical phenomena on the destruction of the valve to improve the service life of high-pressure valve. Among the many structures, Hualin Company designs anti-cavitation high-pressure valves according to the principle of "simplicity is beauty". It not only has the advantages of simple structure and convenient maintenance, but also mainly solves the problem of short life of high-pressure valves and enjoys fame in China. First, the reasons for the short valve life caused by the short life of high-pressure valve there are two main reasons: cavitation, erosion. Flash, Cavitation If the pressure difference across the valve (P1-P2) is greater than the maximum saturated differential pressure (ΔPmax) of the medium, a flash occurs and vapor cavitation is re-created and the internal and adjacent Near the pipeline structure caused damage. The velocity of the medium is maximized when the medium passes through the orifice with the smallest cross section. The increase in flow velocity (or kinetic energy) is accompanied by a significant decrease in pressure (or potential energy). When the pressure is lower than the saturated vapor pressure of the medium, bubbles form in the medium. As the pressure at the orifice drops further, bubbles can form in large numbers. There is no essential difference between flash and cavitation at this stage, but the possibility of structural damage to the valve is certain. Flash, erosion: If the medium passes through the orifice, the pressure is still below the saturated steam pressure of the medium. Bubbles will remain in the stream behind the orifice, which we call flashing. Flashing on the valve spool will have serious erosion damage, which is characterized by the erosion of the surface smooth and polished appearance, as shown in Figure 9-3. The area with the most erosion damage is usually the area with the highest flow rate, usually on or near the contact line between the valve plug and seat. Especially in the small opening, small throttle clearance, high velocity environment, the erosion damage is also the most serious. Therefore, high-pressure valve should try to avoid a small opening work. Even the best of the valve, if long-term work in a small opening, its life will be doubled. To avoid the small opening of the work, the key in the calculation, selection, which is Design Institute and users should pay more attention. Typical contour cavitation damage by flash evaporation: On the other hand, if the medium pressure returns to above the saturated vapor pressure of the medium after passing through the orifice, the bubble will burst or inwards explode, creating cavitation. The rupture of the steam bubble releases energy and produces a noise similar to sand flowing through the valve. If the bubbles burst near the solid surface inside the valve, the energy released will slowly tear the material, leaving honeycomb holes. The destructive effect of cavitation may extend to the adjacent downstream pipe. Obviously, the high recovery valve is more prone to cavitation from the pressure recovery factor because its post-orifice pressure is more likely to rise above the saturated vapor pressure of the medium. The typical shape of cavitation damage and the relationship between cavitation erosion, erosion: a small opening work, throttle flow faster, lower pressure, more bubbles in the media, so the flash destruction More serious, erosion damage is the main contradiction. The main contradiction when working at the opening ceremony is the cavitation damage caused when the system pressure recovers above the saturation pressure. Therefore, users should try their best to avoid the small opening when using high-pressure differential valve. The high-pressure valve manufactured by the manufacturer must have better anti-cavitation measures. Otherwise, the valve will soon be damaged by cavitation erosion and erosion. A mature anti-cavitation high-pressure valve is now the most widely used high-pressure valve from the structural division of the main multi-stage high pressure valve, labyrinth high pressure valve and single-seat sleeve type high-pressure valve load valve and several other categories. From the use of the situation, they have their own advantages, but multi-level and labyrinth high pressure internal structure is more complex, spare parts preparation and replacement more difficult to use very convenient. In response to these circumstances, Hualin company developed a single-seat load-type fine anti-cavitation high pressure valve. The product spare parts is simple, easy to replace and repair, a good solution to the above problems. In 1992 the product won the national patent (patent number: ZL 92 2 20633.3). (The anti-cavitation high-pressure valve structure shown in Figure 9-8. It uses the "orifice + single seat valve + sleeve valve" three throttling structure: ◠a throttle - take-over diameter reduction Equivalent to orifice throttling, accounting for about 10% of the total pressure drop ◠Secondary throttling - single-seat throttling (main throttling, ② Department) single-seat valve structure, accounting for about 30% of the total pressure drop. ◠throttling - sleeve throttling (③ Department) sleeve structure, accounting for about 60% of the total pressure drop. Pneumatic thin film anti cavitation high pressure valve "orifice + single seat valve + sleeve valve" three throttling The structure divides the pressure drop across the valve into a number of smaller pressure drops. Each smaller pressure drop ensures that the minimum pressure at the throttling face is greater than the saturated vapor pressure, avoiding or mitigating the damaging effect of the flashover on the valve. At the same time, the small-hole injection-type sleeve choke instead of the conventional "guide bushing + seat" mode can completely cure the problem that the guide bush is easy to loose, and the orifice jet throttling structure can reduce the anti-flow One side of the valve seat seat is partially damaged, reducing the throttle 喑 sound. Because the orifice injection mode withstands most of the valve throttle pressure drop (about 60%), the cavitation The bad effect moves to the small hole by the valve seat, has protected the sealing surface, has raised the service life of the valve, can reach 2 ~ 3 times of the ordinary high-pressure difference valve. 三, Anti-cavitation measures (1) In the past does not use the hard alloy way (2) In the 1970s, the valve was often used to set the orifice technology to reduce the pressure drop on the valve, so as to reduce the pressure drop on the valve, Use this idea can be set within the valve resistance, to achieve better antihypertensive effect. (3) to prevent small opening work, reduce the speed of flushing fluid (4) select the fluid to change as small as the valve, such as straight stroke angle valve (5) The deflection will cause serious local erosion, should be used to disperse the spoiler method to overcome. (6) The use of multi-stage throttling structure, the pressure drop through the valve is divided into several smaller Of the pressure drop to improve valve life. (7) Increase the stem diameter, stem stiffness to prevent fracture. (8) Large diameter, large pressure differential, should be equipped with powerful piston-type actuator. Fourth, the use of precautions (1) Preventing the work of small openings is the key, and the work of small openings will multiply the life span Selection of such cases, should be reduced DN or dg; (2) for large-diameter valve, you must carefully calculate the unbalanced force, select the actuator and the spring range, to prevent the valve is not in place; (3) on the caliber (4) 95 years of chemical industry notified a chemical plant due to the spool rupture, flow closed high-pressure valve (side-in and out ) Valve head automatically shut down, the pressure rises, leading to equipment explosion, causing serious casualties. Therefore, from a safety point of view, should be used to open type (bottom side) Regulating valve
