Common troubleshooting of the hottest regulating v

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Treatment of common faults of regulating valve (4)

1) for oscillation and slight vibration, the stiffness can be increased to eliminate or weaken, such as selecting a spring with large stiffness and changing to a piston actuator, etc

2) increasing damping means increasing the friction to vibration. For example, the valve plug of sleeve valve can be sealed with "O" ring, and graphite packing with large friction can be used, which still has a certain effect on eliminating or weakening slight vibration

3) by increasing the guide size and reducing the fitting clearance, the guide size of axial plug valves is generally small, and the fitting clearance of all valves is generally large, with 0.4 ~ LMM, which is helpful to produce mechanical vibration. Therefore, in case of slight mechanical vibration, the vibration can be weakened by increasing the guide size and reducing the fitting clearance

4) change the shape of the throttle and eliminate the resonance method. Because the so-called vibration source of the regulating valve occurs at the throttle port with high-speed flow and sharp pressure changes, changing the shape of the throttle can change the frequency of the vibration source, which is easier to solve when the resonance is not strong. The specific method is to turn the valve core surface within the range of vibration opening by 0.5 ~ 1.0mm. For example, a self operated pressure regulating valve was installed near the family area of a factory, and the roar caused by resonance affected the rest of employees. After we dropped the valve core surface by 0.5mm, the resonant roar disappeared

5) the principle of replacing throttling parts and eliminating resonance method is the same as 4 in 4.5), which is just replacing throttling parts. The methods include: ① changing the flow characteristics, changing logarithm to linearity, and changing linearity to logarithm; ② Change the valve element type. For example, change the shaft plug shape to "V" groove spool, and change the double seat valve shaft plug type to sleeve type; Change the sleeve opening the window into a sleeve with a small hole, etc. For example, a DN25 double seat valve in a nitrogenous fertilizer plant often vibrates and breaks at the connection between the valve stem and the valve core. After we confirm that it is resonance, we change the linear characteristic valve core to the logarithmic valve core, and the problem is solved. Another example is that a DN200 sleeve valve is used in the laboratory of an aeronautical college, and the valve plug cannot be put into use due to strong rotation. After changing the sleeve with a window to a sleeve with a small hole, the rotation disappears immediately

6) change the type of regulating valve to eliminate resonance The natural frequencies of control valves with different structural forms are naturally different. Replacing control valves and using information systems to improve the intelligent level of production, manufacturing and sales process is the most effective way to fundamentally eliminate resonance. The resonance of a valve in use is very strong - a valve with strong vibration (which can destroy the valve in serious cases), strong rotation (even the valve rod is broken and twisted), and strong noise (up to more than 100 decibels), as long as it is replaced with a valve with large structural differences, it will take effect immediately, and the strong resonance will miraculously disappear. For example, a DN200 sleeve valve is selected for the new expansion project of a vinylon plant, and the above three phenomena exist. The DN300 pipeline jumps with it, the valve plug rotates, the noise is more than 100 dB, and the resonance opening is 20 ~ 70%. Considering the large resonance opening, after using a double seat valve, the resonance disappears and the operation is normal

7) cavitation vibration reduction method for cavitation vibration caused by cavitation bubble rupture, it is natural to find ways to reduce cavitation. ① The impact energy generated by bubble rupture does not act on the solid surface, especially on the valve core, but is absorbed by the liquid. Sleeve valve has this feature, so the shaft plug type spool can be changed to sleeve type. ② Take all measures to reduce cavitation, such as increasing throttling resistance, increasing constriction port pressure, grading or * decompression, etc

8) avoid the vibration source wave strike method. The valve vibration caused by the external vibration source wave strike is obviously something that should be avoided during the normal operation of the control valve. If this vibration occurs, corresponding measures should be taken

solutions when the stability of the control valve is poor

1) change the action of the unbalanced force using the direction method. In the stability analysis, it is known that the unbalanced force has the same effect as the valve closing direction, that is, when the valve has a closing trend, the valve stability is poor. When the valve works under the above unbalanced force conditions, the method of changing its action direction is usually to change the flow closed type to the flow open type. Generally speaking, it can easily solve the problem that some alloys of the valve, such as 2XXX series alloys with high alloying, 7xxx series alloys, 5xxx series alloys with Mg content greater than 6%, aluminum lithium alloys, aluminum scandium alloys, etc., cannot be produced, let alone the stability of mass production

2) avoid working in the unstable area of the valve itself. Some valves are limited by their own structure and have poor stability when working at some openings. ① The opening of the double seat valve is less than 10%, which brings instability problems because the upper ball flows open and the lower ball flows closed; ② The stability is poor near the alternating slope of the unbalanced force. Such as butterfly valve, the alternating point is about 70 degrees; The double seat valve is at 80 ~ 90% opening. In case of such a valve, the stability will be poor when working in the unstable area, so it is enough to avoid working in the unstable area

3) replace the valve with good stability. The valve with good stability has small change in unbalanced force and good guidance. Among the commonly used ball valves, sleeve valves have this major feature. When the stability of single and double seat valves is poor, the stability of sleeve valve will be improved

4) the ability of the actuator to resist the impact of load changes on travel depends on the spring stiffness. The greater the stiffness, the smaller the impact on travel, and the better the stability of the valve. Increasing the spring stiffness is a common and simple method to improve the stability of the valve, such as changing the spring in the range of 20 ~ 100KPA into a large stiffness spring in the range of 60 ~ 180kpa. This method is mainly used for the valve with a positioner, otherwise, the valve used should be equipped with a positioner

5) reduce response speed method when the system requires that the response of the regulating valve or the regulation speed should not be too fast, the response and regulation speed of the valve is faster. For example, the flow needs to be fine tuned, but the flow regulation of the regulating valve changes greatly, or the system itself is a fast response system, but the regulating valve is equipped with a positioner to speed up the action of the valve, which is unfavorable. This will cause overshoot, vibration, etc. In this regard, the response speed should be reduced. The methods are: ① change the linear characteristic into logarithmic characteristic; ② Those with positioners can be changed into converters and relays

6) change the flow direction, solve the problem of closing and eliminating surge. In order to improve the cutting effect, the two position valve is usually used as a flow closed type. For liquid media, because the action of flow closing unbalanced force is to close the valve core, it has the function of promoting closing, also known as suction, which accelerates the action speed of the valve core, produces a slight water hammer, and causes the system surge. The solution to the above phenomenon is to change the flow direction to flow away, and the surge can be eliminated. Similar problems that affect the normal operation of the valve due to closing promotion can also be solved by this method

7) the most typical valve to overcome the fluid damage method is the double seat valve. The fluid enters from the middle, the valve core is perpendicular to the inlet, and the fluid bypasses the valve core and flows out in two bundles. The fluid impacts on the valve core, making it close to the outlet side, causing friction, damaging the guide surface of the valve core and bushing, resulting in abnormal action. High flow may also make the valve core bend, erode, or even break in serious cases. Solutions: ① improve the material hardness of the guide part; ② Increase the middle size of the upper and lower balls of the valve core, so that it is wrapped in layers; ③ Use other valves instead. If a sleeve valve is used, the fluid flows around the sleeve, and the lateral thrust on the valve plug is greatly reduced

8) the method of overcoming the rotating force generated by the fluid to make the valve core rotate. For the valve core with "V" shaped port, due to the asymmetry of medium inflow, the tangential force acting on the valve core with "V" shaped port is inconsistent, resulting in a rotating force to make it rotate. Especially for valves with DN ≥ 100. As a result, the valve may be disconnected from the actuator push rod, and the spring-free actuator may cause the diaphragm to twist. The solutions are: ① turn the reverse rotation direction of the valve core by an angle to balance the tangential force acting on the valve core; ② Further lock the connection between the valve rod and the push rod, and if necessary, add an anti rotation splint; ③ Replace the valve core with a "V" shaped opening with a plunger shaped valve core; ④ Adopt or change to sleeve structure; ⑤ If the rotation is caused by resonance, the problem can be solved by eliminating resonance

9) adjust the friction of the butterfly valve plate, overcome the opening jump method, and use the butterfly valve with soft seal such as "O" ring, sealing ring and lining. When the valve is closed, due to the deformation of the soft seal, the valve plate is closed in place and covers the valve plate, which can achieve a very ideal cutting effect. However, when the valve is to be opened, the force of the actuator to open the valve plate continues to increase. When the friction between the soft seal and the valve plate is equal, the valve plate starts. Once activated, this friction decreases dramatically. 4.2 the parts of steel parts that are often twisted and easy to wear should be heat treated. In order to achieve the balance of force, the valve plate opens violently. When this force is balanced with the unbalanced torque of the medium with the corresponding opening and the opening torque of the actuator, the valve stops at this opening. This violent and sudden take-off opening can be as high as 30 ~ 50%, which will cause a series of problems. At the same time, due to the large changes of the soft seal during closing, it is easy to produce permanent deformation or be crushed and strained by the valve plate, which will affect the service life. The solution is to adjust the friction force of the soft seal on the valve plate startup, which can not only ensure the required cut-off requirements, but also make the valve start more normally. The specific methods are: ① adjust the interference; ② By limiting or adjusting the preload and output force of the actuator, the difficulty of opening caused by excessive closing of the valve plate can be reduced

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