In industrial automation instruments, regulating valves are bulky, combined with simple structures that are often not valued by people. However, it is in the process pipeline, and the working conditions are complex. Once problems arise, everyone is busy. Due to its bulkiness, the problem is difficult to identify, often unpleasant, but also involves the system put into operation, the system is completely, adjust the quality, environmental pollution and so on.
First, the method to improve life (8 methods)
1) Wide open work life extension method
Let the regulating valve work as far as possible at the maximum opening, such as 90%. In this way, cavitation, erosion, and other damage occur at the head of the valve plug. With the destruction of the valve core, the flow increases, and the corresponding valve is closed a bit, so that it continues to be destroyed and gradually closed, making full use of the entire spool, until the valve core and sealing surface damage, can not be used. At the same time, the wide opening of the work to throttling clearance, erosion weakened, which is more than the beginning of the valve to work in the middle and small opening degree to improve the life of 1 to 5 times. If a chemical plant adopts this method, the service life of the valve is increased by 2 times.
2) Decrease S increase working opening increase lifespan method
Decreasing S means increasing the loss of the system except the regulating valve, so that the pressure drop distributed to the valve is reduced. In order to ensure that the flow passes through the regulating valve, the opening degree of the regulating valve must be increased, and at the same time, the pressure drop on the valve is reduced, so that Cavitation erosion and erosion are also weakened. The specific measures include: after the valve orifice plate orifice throttling consumption pressure drop; close the pipeline on the series of manual valve, to the regulator valve to obtain a more ideal job opening so far. It is very simple, convenient, and effective to use this method when the valve selection is large and it is at a small opening degree.
3) Reducing the diameter and increasing the opening degree of the working life cycle
The opening of the valve can be increased by reducing the valve diameter. The specific measures include: 1 changing the valve of a small one-step diameter, such as DN32 replaced by DN25; 2 the valve body is not changed, replace the valve valve of the small valve seat diameter seat. For example, when a chemical plant is overhauled, replacing the dgl0 with dg8 will increase the life expectancy by a factor of two.
4) Transfer of damage to the location of life-enhancing method
Move the severely damaged area to a secondary position to protect the sealing surface and the throttle surface of the valve seat.
5) Increased throttling passage to increase lifespan
The simplest way to increase the throttling channel is to thicken the valve seat so that the valve seat hole grows to form a longer throttling channel. On the one hand, it is possible to delay the sudden expansion of the closed flow throttling, to transfer the damaged position away from the sealing surface, and on the other hand, to increase the throttling resistance and reduce the recovery of the pressure. Erosion weakened. Some of the valve seat holes designed to step-style, wave-style, is to increase resistance and weaken cavitation. This method is also very effective when used in the introduction of high pressure valves in installations and when the older valves are improved.
6) Changing the flow direction to improve life
Flow-opening flow toward the open direction, cavitation, erosion mainly on the sealing surface, so that the valve core and the valve seat sealing surface quickly suffer damage; flow closed toward the closed direction, cavitation, erosion effect After throttling, the valve seat sealing surface below, to protect the sealing surface and the valve core, to extend the life. Precautionary use of the open-type valve, when the problem of prolonged life is more prominent, just change the flow to extend the life of 1 to 2 times.
7) Switch to special material to improve life cycle method
For cavitation resistance (breaking shapes such as honeycomb dots) and flushing (streamlined minor grooves), special materials resistant to cavitation and erosion can be used to manufacture throttles. This special material is 6YC-1, A4 steel, Stellite, cemented carbide and so on. For corrosion resistance, materials that are more resistant to corrosion and have certain mechanical and physical properties can be used instead. This material is divided into non-metallic materials (such as rubber, PTFE, ceramics, etc.) and metal materials (such as Monel, Hastelloy, etc.).
8) Change valve structure to increase lifespan method
Take the change of valve structure or use a valve with a longer life to achieve the purpose of improving life, such as the use of multi-stage valve, anti-cavitation valve, anti-corrosion valve.
Second, the control valve often stuck or blocked anti-blocking (card) method (6 methods)
1) Cleaning method
The welding slag, rust, slag, etc. in the pipeline cause blockage or jamming in the throttle orifice, the guide part, and the lower bonnet balance hole, causing the valve core surface and guide surface to be scratched and scratched, and the sealing surface is indented. Wait. This often happens during the initial period after the new commissioning system and overhaul. This is the most common fault. In this case, it must be unloaded for cleaning, remove the slag, if the sealing surface is damaged, it should be ground; at the same time, the bottom plug should be opened to flush the slag dropped from the balance hole into the lower valve cover and the pipeline Rinse. Before commissioning, let the regulating valve fully open, and the medium will flow into normal operation after flowing for a period of time.
2) External flushing
For some easy-to-precipitate, solid-particle containing media using ordinary valve adjustment, often blocked in the throttle, guide, can be attached to the bottom of the bottom valve cover flushing gas and steam. When the valve is blocked or stuck, open the external gas or steam valve, you can complete the flushing operation without adjusting the valve, so that the valve can run normally.
3) Install pipe filter method
For the small-diameter control valve, especially the ultra-small flow control valve, the throttling clearance is very small, there can not be a little slag in the medium. In the event of a blockage, it is advisable to install a filter on the valve front to ensure that the medium passes through. With the regulator used in the positioner, the positioner is not working properly, and the blockage of the throttle orifice is the most common failure. Therefore, when working with the positioner, it is necessary to handle the gas source. The commonly used method is to install an air filter pressure reducing valve on the gas line in front of the positioner.
4) Increase the throttle gap method
If the solid granules in the medium or the slag and rust that has been washed away from the pipes, etc., cannot be blocked or stuck due to the throttle opening, the throttling device with a large throttling gap may be used. The throttling area is opened. Valves and sleeves of windows and openings are easily excluded because they have a concentrated throttle area rather than a circular distribution. If it is a single or double seat valve, the plunger-shaped valve core can be changed to a "V"-shaped valve core or a sleeve valve. For example, a chemical plant has a double-seat valve that often jams. After the sleeve valve is recommended, the problem is immediately solved.
5) Media flushing
Using the media's own flushing energy, it can scour and carry away the easy-to-precipitate and easy-clogging things, thereby increasing the anti-blocking function of the valve. Common methods are: 1 to change the flow closed type use; 2 using streamlined valve body; 3 the throttle is placed in the most powerful erosion, the use of this method should pay attention to improve the erosion resistance of the throttle material.
6) Straight through to angle method
Straight through to the inverted S flow, the flow path is complex, and the dead space of the upper and lower chambers provides a place for the sedimentation of the medium. Angle connection, the medium is like a 90° elbow, good erosion performance, small dead zone, easy to design into a streamlined shape. Therefore, when using a straight-through regulator valve to produce a slight blockage, it can be used as an angle valve.
Third, the solution to control valve leakage (6 methods)
1) Increase the seal grease method For valves that do not use sealed grease, consider increasing the seal grease to improve the stem seal performance.
2) Adding packing method To increase the sealing performance of the packing to the valve stem, a method of increasing the packing may be used. Double-layer and multi-layer mixed fillers are usually used. Simply increasing the number, for example, 3 to 5, is not effective.
3) Replacement of graphite filler used in a large number of PTFE filler, because its operating temperature in the range of -20 ~ +200 °C, when the temperature in the upper and lower limit, a large change, the seal will be significantly reduced, aging fast, life short. Flexible graphite fillers overcome these shortcomings and have a long service life. As a result, some plants have changed their PTFE fillers to graphite fillers, and even newly-recovered control valves have been replaced with graphite fillers. However, the difference in the use of graphite fillers is large, and some creeping phenomenon occurs at the beginning, which must be taken into consideration.
4) Change the direction of flow, set P2 at the stem end When the â–³P is large and P1 is large, the seal P1 is obviously more difficult than the seal P2. Therefore, the method of changing the flow direction can be adopted to change P1 from the stem end to P2 stem end, which is more effective for valves with high pressure and large pressure difference. Such as the bellows valve should normally consider the seal P2. 5) using the lens gasket sealing method for the upper and lower cover seals, the valve seat and the upper and lower valve body seal. If it is a flat seal, under the condition of high temperature and high pressure, the sealing performance is poor, causing leakage, and it can be replaced with a lens mat to achieve satisfactory results.
6) Replacement of gaskets Most gaskets still use asbestos plates. At high temperatures, the sealing performance is poor and the service life is short, causing leakage. In this case, spiral wound gaskets, “O†rings, etc., can be used instead. Now many plants have adopted them.
Fourth, adjust valve vibration solution (8 methods)
1) Increase the stiffness method for vibration and slight vibration, can increase the stiffness to eliminate or weaken, such as the selection of large spring stiffness, the use of piston actuators and other methods are feasible.
2) increase the damping method to increase the damping that increases the friction of the vibration, such as sleeve valve plug can be used "O" ring seal, the use of graphite filler with greater friction, etc., which eliminate or weaken the slight vibration There is a role.
3) Increase the guide dimension, reduce the fit clearance method The general guide dimension of the plug-type valve is smaller, and all valve fit clearances are generally larger, with 0.4 ~ lmm, which is helpful for generating mechanical vibration. Therefore, when a slight mechanical vibration occurs, the vibration can be weakened by increasing the guide dimension and reducing the fit clearance.
4) Change the shape of the throttling element and eliminate the resonance method Since the so-called vibration source of the control valve occurs at the throttling port where the high-speed flow and the pressure change drastically, changing the shape of the throttling element can change the frequency of the vibration source, and compare when the resonance is not strong. Easy to solve. The specific method is to turn the surface of the valve core in the range of vibration opening by 0.5 to 1.0 mm. If a manufacturer's own area near the installation of a self-operated pressure regulating valve, due to the resonance generated a whistle affecting the rest of the staff, we will 0.5mm off the surface of the valve surface after the car, the resonance whistling sound disappeared.
5) Replacing the throttling piece to eliminate the resonance method: 1 Change the flow characteristics, change the logarithm to linear, change the logarithm linearly; 2 replace the spool form. If the plug shape is changed to a "V"-shaped slot valve, the double-seat valve plug type will be changed to a sleeve type; the windowed sleeve will be changed to a small-hole sleeve. If a nitrogen fertilizer plant has a DN25 double seat valve, the connection between the valve stem and the valve core often vibrates. After we confirm that it is resonant, we will change the linear characteristic spool to a logarithmic spool. The problem is solved. Another example is the use of a DN200 sleeve valve in an academy's laboratory. The valve plug produces a strong rotation and cannot be used. After the windowed sleeve is changed to a sleeve with a small hole, the rotation immediately disappears.
6) Replace the regulator valve type to eliminate resonance.
Different types of control valves naturally have different natural frequencies. Changing the type of control valve is the most effective way to fundamentally eliminate resonance. Resonance of a valve in use is very powerful - vibrate strongly (in case of severe damage to the valve), strongly rotate (even the valve stem is broken, broken), and produce a strong noise (up to more than 100 decibels) The valve, as long as it is replaced with a valve with a large structural difference, will immediately take effect and the strong resonance will disappear miraculously. For example, if a DN200 sleeve valve is selected for a new expansion project of the Vinylon plant, all three phenomena mentioned above will occur. The DN300's pipe will jump, the valve plug will rotate, the noise will be more than 100 decibels, and the resonance opening will be 20-70%. Consider resonance. When it was too big, after using a two-seat valve, the resonance disappeared and it was put into operation.
7) To reduce the cavitation vibration caused by the cavitation bubble rupture in the cavitation vibration method, it is natural to find ways to reduce cavitation. 1 The impact energy generated by the rupture of the bubble does not act on the solid surface, especially the valve plug, but allows the liquid to absorb it. The sleeve valve has this feature, so it is possible to change the plug-type spool to a sleeve type. 2 to take all measures to reduce cavitation, such as increasing throttling resistance, increasing the pressure of the reducing orifice, grading or decompression in series.
8) Avoid the vibration of the valve caused by the vibration of the external source of the vibration source wave. This is obviously the time that should be avoided when the control valve works normally. If such vibration occurs, corresponding measures should be taken.
Seven, large noise control valve solution (8 methods)
1) Elimination of the resonance noise method Only when the control valve is in resonance, there is an energy superposition and a strong noise of more than 100 decibels. Some have strong vibrations, little noise, some weak vibrations, and very loud noises; some have large vibrations and noise. This noise produces a monotonic sound that typically has a frequency of 3000-7000 Hz. Obviously, with the elimination of resonance, noise naturally disappears. For methods and examples, see 4), 5), and 6) in 4.5 above.
2) Elimination of cavitation noise cavitation is the main source of fluid dynamic noise. When cavitation occurs, bubbles burst to generate high-speed impacts, causing strong local turbulence and cavitation noise. This noise has a wide frequency range, creating a rattling sound that is similar to the sound produced by gravel in fluids. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
3) The use of thick-walled pipe method is one of the sound path treatment methods. The use of thin walls can increase the noise by 5 dB, and the use of thick-walled tubes can reduce the noise by 0-20 dB. The thicker the same pipe wall, the larger the pipe diameter of the same wall thickness, the better the noise reduction effect. Such as DN200 pipe, the wall thickness were 6.25,6.75,8,10,12.5,15,18,20,21.5mm, can reduce the noise were -3.5, -2 (that is, increase), 0, 3, 6, 8,11,13,14.5 dB. Of course, the thicker the wall, the higher the cost.
Eight, the valve vibration solution (8 methods)
1) Increase the stiffness method for vibration and slight vibration, can increase the stiffness to eliminate or weaken, such as the selection of large spring stiffness, the use of piston actuators and other methods are feasible.
2) increase the damping method to increase the damping that increases the friction of the vibration, such as the sleeve valve plug can be used "O" ring seal, the use of graphite filler with greater friction, etc., which eliminate or weaken the slight vibration There is a role.
3) Increase the guide dimension, reduce the fit clearance method The general guide dimension of the plug-type valve is smaller, and all valve fit clearances are generally larger, with 0.4 ~ lmm, which is helpful for generating mechanical vibration. Therefore, when a slight mechanical vibration occurs, the vibration can be weakened by increasing the guide dimension and reducing the fit clearance.
4) Change the shape of the throttling element and eliminate the resonance method Since the so-called vibration source of the control valve occurs at the throttling port where the high-speed flow and the pressure change drastically, changing the shape of the throttling element can change the frequency of the vibration source, and compare when the resonance is not strong. Easy to solve. The specific method is to turn the surface of the valve core in the range of vibration opening by 0.5 to 1.0 mm. If a manufacturer's own area near the installation of a self-operated pressure regulating valve, due to the resonance generated a whistle affecting the rest of the staff, we will 0.5mm off the surface of the valve surface after the car, the resonance whistling sound disappeared.
5) Replacing the throttling piece to eliminate resonance The principle is the same as 4) in 4.5, except that the throttling element is replaced. The methods are: 1 change the flow characteristics, logarithm change linear, linear logarithm; 2 replace the spool form. If the plug shape is changed to a "V"-shaped slot valve, the double-seat valve plug type will be changed to a sleeve type; the windowed sleeve will be changed to a small-hole sleeve. If a nitrogen fertilizer plant has a DN25 double seat valve, the connection between the valve stem and the valve core often vibrates. After we confirm that it is resonant, we will change the linear characteristic spool to a logarithmic spool. The problem is solved. Another example is the use of a DN200 sleeve valve in an academy's laboratory. The valve plug produces a strong rotation and cannot be used. After the windowed sleeve is changed to a sleeve with a small hole, the rotation immediately disappears.
6) Replace the regulator valve type to eliminate resonance.
Different types of control valves naturally have different natural frequencies. Changing the type of control valve is the most effective way to fundamentally eliminate resonance. Resonance of a valve in use is very powerful - vibrate strongly (in case of severe damage to the valve), strongly rotate (even the valve stem is broken, broken), and produce a strong noise (up to more than 100 decibels) The valve, as long as it is replaced with a valve with a large structural difference, will immediately take effect and the strong resonance will disappear miraculously. For example, if a DN200 sleeve valve is selected for a new expansion project of the Vinylon plant, all three phenomena mentioned above will occur. The DN300's pipe will jump, the valve plug will rotate, the noise will be more than 100 decibels, and the resonance opening will be 20-70%. Consider resonance. When it was too big, after using a two-seat valve, the resonance disappeared and it was put into operation.
7) To reduce the cavitation vibration caused by the cavitation bubble rupture in the cavitation vibration method, it is natural to find ways to reduce cavitation. 1 The impact energy generated by the rupture of the bubble does not act on the solid surface, especially the valve plug, but allows the liquid to absorb it. The sleeve valve has this feature, so it is possible to change the plug-type spool to a sleeve type. 2 to take all measures to reduce cavitation, such as increasing throttling resistance, increasing the pressure of the reducing orifice, grading or decompression in series.
8) Avoid the vibration of the valve caused by the vibration of the external source of the vibration source wave. This is obviously the time that should be avoided when the control valve works normally. If such vibration occurs, corresponding measures should be taken.
Nine, control valve noise solution (8 methods)
1) Elimination of the resonance noise method Only when the control valve is in resonance, there is an energy superposition and a strong noise of more than 100 decibels. Some have strong vibrations, little noise, some weak vibrations, and very loud noises; some have large vibrations and noise. This noise produces a monotonic sound that typically has a frequency of 3000-7000 Hz. Obviously, with the elimination of resonance, noise naturally disappears. For methods and examples, see 4), 5), and 6) in 4.5 above.
2) Elimination of cavitation noise cavitation is the main source of fluid dynamic noise. When cavitation occurs, bubbles burst to generate high-speed impacts, causing strong local turbulence and cavitation noise. This noise has a wide frequency range, creating a rattling sound that is similar to the sound produced by gravel in fluids. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
3) The use of thick-walled pipe method is one of the sound path treatment methods. The use of thin walls can increase the noise by 5 dB, and the use of thick-walled tubes can reduce the noise by 0-20 dB. The thicker the same pipe wall, the larger the pipe diameter of the same wall thickness, the better the noise reduction effect. Such as DN200 pipeline, the wall thickness were 6.25,6.75,8,10,12.5,15,18,20,21.5mm, can reduce the noise were -3.5, -2 (ie increase), 0,3,6, 8,11,13,14.5 dB. Of course, the thicker the wall, the higher the cost.
4) Using sound-absorbing material method This is also a more common and effective method of sound path processing. Sound-absorbing materials can be used to enclose the noise source and the post-valve line. It must be pointed out that because noise can be transmitted over long distances through fluid flow, where the sound-absorbing material is packaged and where the thick-walled pipe is used, the effectiveness of eliminating noise ends. This method is suitable for situations where the noise is not very high and the pipeline is not very long, because it is a more expensive method.
5) Tandem muffler method This method is suitable for use as aerodynamic noise muffler, which can effectively eliminate the noise inside the fluid and suppress the noise level transmitted to the solid boundary layer. This method is most effective and economical for places with high mass flow or high pressure drop ratios before and after the valve. Using an absorption type tandem muffler can significantly reduce noise. However, from an economic point of view, it is generally limited to attenuation of about 25 dB.
6) The soundproof box method uses soundproof boxes, houses and buildings to isolate the noise sources and reduce the noise of the external environment to an acceptable level.
7) Series throttling method When the pressure ratio of the regulating valve is high (ΔP/P1≥0.8), the series throttling method is used to distribute the total pressure drop over the fixed throttling element behind the regulating valve and the valve. If diffusers or porous restrictors are used, this is the most effective method of noise reduction. In order to obtain the best diffuser efficiency, the diffuser (shape and size of the solid) must be designed according to the installation conditions of each piece, so that the noise level generated by the valve and the noise level generated by the diffuser are the same.
8) Selection of low-noise valve The low-noise valve is used to reduce the velocity of the supersonic flow at any point in the flow path according to the gradual deceleration of the fluid through the spiral flow path (multi-channel, multi-channel) of the valve core and valve seat. There are many types of low-noise valves of various structures (designed for special systems) for use when used. When the noise is not too great, the use of a low-noise sleeve valve can reduce the noise by 10 to 20 decibels, which is the most economical low-noise valve.
Tenth, the solution to the poor stability of the control valve (5 methods)
1) Changing the direction of action of the unbalanced force In the stability analysis, when the unbalanced force is known to be the same as the valve closing direction, that is, when the valve is closed, the valve stability is poor. When the valve is operated under the unbalanced force condition, the method of changing the direction of the action is selected. Usually, the flow-closed type is changed to the flow-opening type. Generally, the valve stability problem can be easily solved.
2) Avoiding valve instability in the working area of ​​the valve itself. Some valves are limited by their own structure and have poor stability when working at certain opening degrees. 1 Double-seat valve, opening within 10%, due to flow at the ball, the flow at the ball off, causing instability; 2 imbalance of the change in the imbalance of the force generated near the alternation, its stability is poor. If the butterfly valve, the alternating point is about 70 degrees; the double seat valve is in the 80-90% opening degree. In the event of such a valve, working in an unstable zone will inevitably have poor stability and avoid working in an unstable zone.
3) Replacing the valve with good stability The valve with good stability has a small change in the unbalanced force and is well guided. Commonly used ball valve, sleeve valve has this great feature. When the stability of the single and double seat valves is poor, the stability of the replacement sleeve valve will surely be improved.
4) The ability of the spring stiffness actuator to resist the impact of load changes on the stroke depends on the spring stiffness. The greater the stiffness, the smaller the influence on the stroke and the better the valve stability. Increasing the spring rate is a common and simple way to improve the stability of the valve. For example, changing the spring range from 20 to 100 KPa to a large stiffness spring between 60 and 180 KPa, this method is mainly used with the valve of the positioner, otherwise, it is used. The valve should be equipped with a locator.
5) Decrease the response speed When the system requires the regulating valve to respond or adjust the speed should not be too fast, the valve response and regulation speed is faster, such as the flow needs to be fine-tuned, but the flow adjustment of the regulating valve is very large, or The system itself is already a quick response to the system while the regulator valve has a positioner to accelerate the valve action, which is all unfavorable. This will produce overshoots, vibrations, etc. In this regard, response speed should be reduced. The methods are: 1 change the linear characteristic to logarithmic characteristic; 2 can be changed to the converter and relay with the positioner.
4) Symmetrically screwed bolts, using thin gasket sealing method In the “O†ring-sealed regulating valve structure, when a thick gasket with large deformation (such as a wound sheet) is used, if the compression is asymmetric, the stress is not symmetrical. , It is easy to damage, tilt and deform the seal, which seriously affects the sealing performance. Therefore, in the maintenance and assembly of such valves, the compression bolts must be tightened symmetrically (be careful not to tighten them once). Thick gaskets are better if they can be changed to thin gaskets, which makes it easier to reduce the slope and ensure the seal.
5) The method of increasing the width of the sealing surface to prevent the flat valve core from jumping and reducing the leakage when it closes The flat plate type valve core (such as the valve plug of the two-way valve and the sleeve valve) has no guide and guide surface in the valve seat When the valve is working, the spool is subjected to a lateral force and flows from the flow-in side to the outflow side. The larger the clearance between the spools, the more serious the unilateral phenomenon is, and the deformation, the misalignment, or the sealing surface of the valve core is reversed. The corner is small (usually 30° chamfer to guide), so when close to close, the chamfered end surface of the sealing surface of the valve core is placed on the sealing surface of the valve seat, causing the valve core to jump when closing, or even not closing the position, so that the valve The amount of leakage has greatly increased. The simplest and most effective solution is to increase the size of the sealing surface of the valve plug so that the minimum diameter of the end face of the valve plug is smaller than the diameter of the valve seat by 1 to 5 mm, and there is enough guiding action to ensure that the valve plug is guided into the valve seat. Good sealing surface contact.
6) Change the direction of flow, solve the problem of promotion, and eliminate the surge method The two-way valve is usually used as a closed flow type to improve the cutting effect. For the liquid medium, due to the effect of the flow-closed unbalanced force, the valve core is closed and the closing effect is promoted, which is also called the suction action. This speeds up the movement speed of the valve core, generates a slight water hammer, and causes the system to surge. The solution to the above phenomenon is to simply eliminate the flow by changing the flow direction. Similar problems such as the fact that the valve does not work properly due to the promotion of clearance can also be considered to take this approach.
7) The most typical valve for overcoming the fluid damage method is a double seat valve. The fluid enters from the middle and the valve core is perpendicular to the inlet. The fluid bypasses the valve core and is divided into upper and lower two bundles. The fluid impinges on the spool, causing it to lean against the outlet side, causing friction and damaging the guide surface of the spool and bushing, causing erratic movements. High flow rates may also cause the spool to bend, erode, and severely break. The solution is: 1 to increase the hardness of the guide site material; 2 to increase the middle size of the valve ball up and down to make it rough; 3 use other valve alternatives. If a sleeve valve is used, fluid flows from around the sleeve and the lateral thrust on the valve plug is greatly reduced.
8) Overcoming the rotational force generated by the fluid to make the valve core rotate. For the valve core of the “V†shape, due to the asymmetry of the medium flow, the tangential force of the valve core acting on the “V†shape is inconsistent, resulting in a Rotating rotational force. In particular, valves with DN ≥ 100 are more intense. As a result, the valve may be disengaged from the actuator stem linkage, and the springless actuator may cause the diaphragm to twist. The solutions include: 1 Turn the valve counter-rotation direction to an angle to balance the tangential force acting on the valve plug; 2 Further lock the connection between the valve stem and the push rod, if necessary, add a piece of anti-rotation clamp; 3 Replace the "V" shaped spool with a plunger-type spool; 4 Use or change to a sleeve-type structure; 5 If the resonance is caused by the rotation, eliminate the resonance to solve the problem.
9) Adjust the friction force of the butterfly valve plate, overcome the open-bounce method and adopt the soft sealed butterfly valve such as “O†ring, seal ring and lining. When the valve is closed, due to the deformation of the soft seal, the valve plate is closed in position and the valve is enclosed. The board can achieve a very good cutting effect. However, when the valve is to be opened, the force of the actuator to open the valve plate is continuously increased. When the frictional force of the soft seal to the valve plate is equal, the valve plate starts. Once started, this friction force decreases dramatically. In order to achieve the balance of force, the valve plate opens violently. When this force is balanced with the unbalance torque of the corresponding opening medium and the opening moment of the actuator, the valve stops at this opening. This violent and sudden jump opens up to 30 to 50%, which will create a series of problems. At the same time, due to the soft seal to produce a large change when closed, easy to produce permanent deformation or by the valve plate, such as damage, strain, affect the life. The solution is to adjust the frictional force of the soft seal against the start of the valve plate, which can not only meet the required cutting requirements, but also make the valve start more normally. Specific measures include: 1 adjustment of the amount of interference; 2 limit or adjust the pre-tightening force of the implementing agencies, the output force approach to reduce the excessive closure of the valve plate to open the difficulties.
First, the method to improve life (8 methods)
1) Wide open work life extension method
Let the regulating valve work as far as possible at the maximum opening, such as 90%. In this way, cavitation, erosion, and other damage occur at the head of the valve plug. With the destruction of the valve core, the flow increases, and the corresponding valve is closed a bit, so that it continues to be destroyed and gradually closed, making full use of the entire spool, until the valve core and sealing surface damage, can not be used. At the same time, the wide opening of the work to throttling clearance, erosion weakened, which is more than the beginning of the valve to work in the middle and small opening degree to improve the life of 1 to 5 times. If a chemical plant adopts this method, the service life of the valve is increased by 2 times.
2) Decrease S increase working opening increase lifespan method
Decreasing S means increasing the loss of the system except the regulating valve, so that the pressure drop distributed to the valve is reduced. In order to ensure that the flow passes through the regulating valve, the opening degree of the regulating valve must be increased, and at the same time, the pressure drop on the valve is reduced, so that Cavitation erosion and erosion are also weakened. The specific measures include: after the valve orifice plate orifice throttling consumption pressure drop; close the pipeline on the series of manual valve, to the regulator valve to obtain a more ideal job opening so far. It is very simple, convenient, and effective to use this method when the valve selection is large and it is at a small opening degree.
3) Reducing the diameter and increasing the opening degree of the working life cycle
The opening of the valve can be increased by reducing the valve diameter. The specific measures include: 1 changing the valve of a small one-step diameter, such as DN32 replaced by DN25; 2 the valve body is not changed, replace the valve valve of the small valve seat diameter seat. For example, when a chemical plant is overhauled, replacing the dgl0 with dg8 will increase the life expectancy by a factor of two.
4) Transfer of damage to the location of life-enhancing method
Move the severely damaged area to a secondary position to protect the sealing surface and the throttle surface of the valve seat.
5) Increased throttling passage to increase lifespan
The simplest way to increase the throttling channel is to thicken the valve seat so that the valve seat hole grows to form a longer throttling channel. On the one hand, it is possible to delay the sudden expansion of the closed flow throttling, to transfer the damaged position away from the sealing surface, and on the other hand, to increase the throttling resistance and reduce the recovery of the pressure. Erosion weakened. Some of the valve seat holes designed to step-style, wave-style, is to increase resistance and weaken cavitation. This method is also very effective when used in the introduction of high pressure valves in installations and when the older valves are improved.
6) Changing the flow direction to improve life
Flow-opening flow toward the open direction, cavitation, erosion mainly on the sealing surface, so that the valve core and the valve seat sealing surface quickly suffer damage; flow closed toward the closed direction, cavitation, erosion effect After throttling, the valve seat sealing surface below, to protect the sealing surface and the valve core, to extend the life. Precautionary use of the open-type valve, when the problem of prolonged life is more prominent, just change the flow to extend the life of 1 to 2 times.
7) Switch to special material to improve life cycle method
For cavitation resistance (breaking shapes such as honeycomb dots) and flushing (streamlined minor grooves), special materials resistant to cavitation and erosion can be used to manufacture throttles. This special material is 6YC-1, A4 steel, Stellite, cemented carbide and so on. For corrosion resistance, materials that are more resistant to corrosion and have certain mechanical and physical properties can be used instead. This material is divided into non-metallic materials (such as rubber, PTFE, ceramics, etc.) and metal materials (such as Monel, Hastelloy, etc.).
8) Change valve structure to increase lifespan method
Take the change of valve structure or use a valve with a longer life to achieve the purpose of improving life, such as the use of multi-stage valve, anti-cavitation valve, anti-corrosion valve.
Second, the control valve often stuck or blocked anti-blocking (card) method (6 methods)
1) Cleaning method
The welding slag, rust, slag, etc. in the pipeline cause blockage or jamming in the throttle orifice, the guide part, and the lower bonnet balance hole, causing the valve core surface and guide surface to be scratched and scratched, and the sealing surface is indented. Wait. This often happens during the initial period after the new commissioning system and overhaul. This is the most common fault. In this case, it must be unloaded for cleaning, remove the slag, if the sealing surface is damaged, it should be ground; at the same time, the bottom plug should be opened to flush the slag dropped from the balance hole into the lower valve cover and the pipeline Rinse. Before commissioning, let the regulating valve fully open, and the medium will flow into normal operation after flowing for a period of time.
2) External flushing
For some easy-to-precipitate, solid-particle containing media using ordinary valve adjustment, often blocked in the throttle, guide, can be attached to the bottom of the bottom valve cover flushing gas and steam. When the valve is blocked or stuck, open the external gas or steam valve, you can complete the flushing operation without adjusting the valve, so that the valve can run normally.
3) Install pipe filter method
For the small-diameter control valve, especially the ultra-small flow control valve, the throttling clearance is very small, there can not be a little slag in the medium. In the event of a blockage, it is advisable to install a filter on the valve front to ensure that the medium passes through. With the regulator used in the positioner, the positioner is not working properly, and the blockage of the throttle orifice is the most common failure. Therefore, when working with the positioner, it is necessary to handle the gas source. The commonly used method is to install an air filter pressure reducing valve on the gas line in front of the positioner.
4) Increase the throttle gap method
If the solid granules in the medium or the slag and rust that has been washed away from the pipes, etc., cannot be blocked or stuck due to the throttle opening, the throttling device with a large throttling gap may be used. The throttling area is opened. Valves and sleeves of windows and openings are easily excluded because they have a concentrated throttle area rather than a circular distribution. If it is a single or double seat valve, the plunger-shaped valve core can be changed to a "V"-shaped valve core or a sleeve valve. For example, a chemical plant has a double-seat valve that often jams. After the sleeve valve is recommended, the problem is immediately solved.
5) Media flushing
Using the media's own flushing energy, it can scour and carry away the easy-to-precipitate and easy-clogging things, thereby increasing the anti-blocking function of the valve. Common methods are: 1 to change the flow closed type use; 2 using streamlined valve body; 3 the throttle is placed in the most powerful erosion, the use of this method should pay attention to improve the erosion resistance of the throttle material.
6) Straight through to angle method
Straight through to the inverted S flow, the flow path is complex, and the dead space of the upper and lower chambers provides a place for the sedimentation of the medium. Angle connection, the medium is like a 90° elbow, good erosion performance, small dead zone, easy to design into a streamlined shape. Therefore, when using a straight-through regulator valve to produce a slight blockage, it can be used as an angle valve.
Third, the solution to control valve leakage (6 methods)
1) Increase the seal grease method For valves that do not use sealed grease, consider increasing the seal grease to improve the stem seal performance.
2) Adding packing method To increase the sealing performance of the packing to the valve stem, a method of increasing the packing may be used. Double-layer and multi-layer mixed fillers are usually used. Simply increasing the number, for example, 3 to 5, is not effective.
3) Replacement of graphite filler used in a large number of PTFE filler, because its operating temperature in the range of -20 ~ +200 °C, when the temperature in the upper and lower limit, a large change, the seal will be significantly reduced, aging fast, life short. Flexible graphite fillers overcome these shortcomings and have a long service life. As a result, some plants have changed their PTFE fillers to graphite fillers, and even newly-recovered control valves have been replaced with graphite fillers. However, the difference in the use of graphite fillers is large, and some creeping phenomenon occurs at the beginning, which must be taken into consideration.
4) Change the direction of flow, set P2 at the stem end When the â–³P is large and P1 is large, the seal P1 is obviously more difficult than the seal P2. Therefore, the method of changing the flow direction can be adopted to change P1 from the stem end to P2 stem end, which is more effective for valves with high pressure and large pressure difference. Such as the bellows valve should normally consider the seal P2. 5) using the lens gasket sealing method for the upper and lower cover seals, the valve seat and the upper and lower valve body seal. If it is a flat seal, under the condition of high temperature and high pressure, the sealing performance is poor, causing leakage, and it can be replaced with a lens mat to achieve satisfactory results.
6) Replacement of gaskets Most gaskets still use asbestos plates. At high temperatures, the sealing performance is poor and the service life is short, causing leakage. In this case, spiral wound gaskets, “O†rings, etc., can be used instead. Now many plants have adopted them.
Fourth, adjust valve vibration solution (8 methods)
1) Increase the stiffness method for vibration and slight vibration, can increase the stiffness to eliminate or weaken, such as the selection of large spring stiffness, the use of piston actuators and other methods are feasible.
2) increase the damping method to increase the damping that increases the friction of the vibration, such as sleeve valve plug can be used "O" ring seal, the use of graphite filler with greater friction, etc., which eliminate or weaken the slight vibration There is a role.
3) Increase the guide dimension, reduce the fit clearance method The general guide dimension of the plug-type valve is smaller, and all valve fit clearances are generally larger, with 0.4 ~ lmm, which is helpful for generating mechanical vibration. Therefore, when a slight mechanical vibration occurs, the vibration can be weakened by increasing the guide dimension and reducing the fit clearance.
4) Change the shape of the throttling element and eliminate the resonance method Since the so-called vibration source of the control valve occurs at the throttling port where the high-speed flow and the pressure change drastically, changing the shape of the throttling element can change the frequency of the vibration source, and compare when the resonance is not strong. Easy to solve. The specific method is to turn the surface of the valve core in the range of vibration opening by 0.5 to 1.0 mm. If a manufacturer's own area near the installation of a self-operated pressure regulating valve, due to the resonance generated a whistle affecting the rest of the staff, we will 0.5mm off the surface of the valve surface after the car, the resonance whistling sound disappeared.
5) Replacing the throttling piece to eliminate the resonance method: 1 Change the flow characteristics, change the logarithm to linear, change the logarithm linearly; 2 replace the spool form. If the plug shape is changed to a "V"-shaped slot valve, the double-seat valve plug type will be changed to a sleeve type; the windowed sleeve will be changed to a small-hole sleeve. If a nitrogen fertilizer plant has a DN25 double seat valve, the connection between the valve stem and the valve core often vibrates. After we confirm that it is resonant, we will change the linear characteristic spool to a logarithmic spool. The problem is solved. Another example is the use of a DN200 sleeve valve in an academy's laboratory. The valve plug produces a strong rotation and cannot be used. After the windowed sleeve is changed to a sleeve with a small hole, the rotation immediately disappears.
6) Replace the regulator valve type to eliminate resonance.
Different types of control valves naturally have different natural frequencies. Changing the type of control valve is the most effective way to fundamentally eliminate resonance. Resonance of a valve in use is very powerful - vibrate strongly (in case of severe damage to the valve), strongly rotate (even the valve stem is broken, broken), and produce a strong noise (up to more than 100 decibels) The valve, as long as it is replaced with a valve with a large structural difference, will immediately take effect and the strong resonance will disappear miraculously. For example, if a DN200 sleeve valve is selected for a new expansion project of the Vinylon plant, all three phenomena mentioned above will occur. The DN300's pipe will jump, the valve plug will rotate, the noise will be more than 100 decibels, and the resonance opening will be 20-70%. Consider resonance. When it was too big, after using a two-seat valve, the resonance disappeared and it was put into operation.
7) To reduce the cavitation vibration caused by the cavitation bubble rupture in the cavitation vibration method, it is natural to find ways to reduce cavitation. 1 The impact energy generated by the rupture of the bubble does not act on the solid surface, especially the valve plug, but allows the liquid to absorb it. The sleeve valve has this feature, so it is possible to change the plug-type spool to a sleeve type. 2 to take all measures to reduce cavitation, such as increasing throttling resistance, increasing the pressure of the reducing orifice, grading or decompression in series.
8) Avoid the vibration of the valve caused by the vibration of the external source of the vibration source wave. This is obviously the time that should be avoided when the control valve works normally. If such vibration occurs, corresponding measures should be taken.
Seven, large noise control valve solution (8 methods)
1) Elimination of the resonance noise method Only when the control valve is in resonance, there is an energy superposition and a strong noise of more than 100 decibels. Some have strong vibrations, little noise, some weak vibrations, and very loud noises; some have large vibrations and noise. This noise produces a monotonic sound that typically has a frequency of 3000-7000 Hz. Obviously, with the elimination of resonance, noise naturally disappears. For methods and examples, see 4), 5), and 6) in 4.5 above.
2) Elimination of cavitation noise cavitation is the main source of fluid dynamic noise. When cavitation occurs, bubbles burst to generate high-speed impacts, causing strong local turbulence and cavitation noise. This noise has a wide frequency range, creating a rattling sound that is similar to the sound produced by gravel in fluids. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
3) The use of thick-walled pipe method is one of the sound path treatment methods. The use of thin walls can increase the noise by 5 dB, and the use of thick-walled tubes can reduce the noise by 0-20 dB. The thicker the same pipe wall, the larger the pipe diameter of the same wall thickness, the better the noise reduction effect. Such as DN200 pipe, the wall thickness were 6.25,6.75,8,10,12.5,15,18,20,21.5mm, can reduce the noise were -3.5, -2 (that is, increase), 0, 3, 6, 8,11,13,14.5 dB. Of course, the thicker the wall, the higher the cost.
Eight, the valve vibration solution (8 methods)
1) Increase the stiffness method for vibration and slight vibration, can increase the stiffness to eliminate or weaken, such as the selection of large spring stiffness, the use of piston actuators and other methods are feasible.
2) increase the damping method to increase the damping that increases the friction of the vibration, such as the sleeve valve plug can be used "O" ring seal, the use of graphite filler with greater friction, etc., which eliminate or weaken the slight vibration There is a role.
3) Increase the guide dimension, reduce the fit clearance method The general guide dimension of the plug-type valve is smaller, and all valve fit clearances are generally larger, with 0.4 ~ lmm, which is helpful for generating mechanical vibration. Therefore, when a slight mechanical vibration occurs, the vibration can be weakened by increasing the guide dimension and reducing the fit clearance.
4) Change the shape of the throttling element and eliminate the resonance method Since the so-called vibration source of the control valve occurs at the throttling port where the high-speed flow and the pressure change drastically, changing the shape of the throttling element can change the frequency of the vibration source, and compare when the resonance is not strong. Easy to solve. The specific method is to turn the surface of the valve core in the range of vibration opening by 0.5 to 1.0 mm. If a manufacturer's own area near the installation of a self-operated pressure regulating valve, due to the resonance generated a whistle affecting the rest of the staff, we will 0.5mm off the surface of the valve surface after the car, the resonance whistling sound disappeared.
5) Replacing the throttling piece to eliminate resonance The principle is the same as 4) in 4.5, except that the throttling element is replaced. The methods are: 1 change the flow characteristics, logarithm change linear, linear logarithm; 2 replace the spool form. If the plug shape is changed to a "V"-shaped slot valve, the double-seat valve plug type will be changed to a sleeve type; the windowed sleeve will be changed to a small-hole sleeve. If a nitrogen fertilizer plant has a DN25 double seat valve, the connection between the valve stem and the valve core often vibrates. After we confirm that it is resonant, we will change the linear characteristic spool to a logarithmic spool. The problem is solved. Another example is the use of a DN200 sleeve valve in an academy's laboratory. The valve plug produces a strong rotation and cannot be used. After the windowed sleeve is changed to a sleeve with a small hole, the rotation immediately disappears.
6) Replace the regulator valve type to eliminate resonance.
Different types of control valves naturally have different natural frequencies. Changing the type of control valve is the most effective way to fundamentally eliminate resonance. Resonance of a valve in use is very powerful - vibrate strongly (in case of severe damage to the valve), strongly rotate (even the valve stem is broken, broken), and produce a strong noise (up to more than 100 decibels) The valve, as long as it is replaced with a valve with a large structural difference, will immediately take effect and the strong resonance will disappear miraculously. For example, if a DN200 sleeve valve is selected for a new expansion project of the Vinylon plant, all three phenomena mentioned above will occur. The DN300's pipe will jump, the valve plug will rotate, the noise will be more than 100 decibels, and the resonance opening will be 20-70%. Consider resonance. When it was too big, after using a two-seat valve, the resonance disappeared and it was put into operation.
7) To reduce the cavitation vibration caused by the cavitation bubble rupture in the cavitation vibration method, it is natural to find ways to reduce cavitation. 1 The impact energy generated by the rupture of the bubble does not act on the solid surface, especially the valve plug, but allows the liquid to absorb it. The sleeve valve has this feature, so it is possible to change the plug-type spool to a sleeve type. 2 to take all measures to reduce cavitation, such as increasing throttling resistance, increasing the pressure of the reducing orifice, grading or decompression in series.
8) Avoid the vibration of the valve caused by the vibration of the external source of the vibration source wave. This is obviously the time that should be avoided when the control valve works normally. If such vibration occurs, corresponding measures should be taken.
Nine, control valve noise solution (8 methods)
1) Elimination of the resonance noise method Only when the control valve is in resonance, there is an energy superposition and a strong noise of more than 100 decibels. Some have strong vibrations, little noise, some weak vibrations, and very loud noises; some have large vibrations and noise. This noise produces a monotonic sound that typically has a frequency of 3000-7000 Hz. Obviously, with the elimination of resonance, noise naturally disappears. For methods and examples, see 4), 5), and 6) in 4.5 above.
2) Elimination of cavitation noise cavitation is the main source of fluid dynamic noise. When cavitation occurs, bubbles burst to generate high-speed impacts, causing strong local turbulence and cavitation noise. This noise has a wide frequency range, creating a rattling sound that is similar to the sound produced by gravel in fluids. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
3) The use of thick-walled pipe method is one of the sound path treatment methods. The use of thin walls can increase the noise by 5 dB, and the use of thick-walled tubes can reduce the noise by 0-20 dB. The thicker the same pipe wall, the larger the pipe diameter of the same wall thickness, the better the noise reduction effect. Such as DN200 pipeline, the wall thickness were 6.25,6.75,8,10,12.5,15,18,20,21.5mm, can reduce the noise were -3.5, -2 (ie increase), 0,3,6, 8,11,13,14.5 dB. Of course, the thicker the wall, the higher the cost.
4) Using sound-absorbing material method This is also a more common and effective method of sound path processing. Sound-absorbing materials can be used to enclose the noise source and the post-valve line. It must be pointed out that because noise can be transmitted over long distances through fluid flow, where the sound-absorbing material is packaged and where the thick-walled pipe is used, the effectiveness of eliminating noise ends. This method is suitable for situations where the noise is not very high and the pipeline is not very long, because it is a more expensive method.
5) Tandem muffler method This method is suitable for use as aerodynamic noise muffler, which can effectively eliminate the noise inside the fluid and suppress the noise level transmitted to the solid boundary layer. This method is most effective and economical for places with high mass flow or high pressure drop ratios before and after the valve. Using an absorption type tandem muffler can significantly reduce noise. However, from an economic point of view, it is generally limited to attenuation of about 25 dB.
6) The soundproof box method uses soundproof boxes, houses and buildings to isolate the noise sources and reduce the noise of the external environment to an acceptable level.
7) Series throttling method When the pressure ratio of the regulating valve is high (ΔP/P1≥0.8), the series throttling method is used to distribute the total pressure drop over the fixed throttling element behind the regulating valve and the valve. If diffusers or porous restrictors are used, this is the most effective method of noise reduction. In order to obtain the best diffuser efficiency, the diffuser (shape and size of the solid) must be designed according to the installation conditions of each piece, so that the noise level generated by the valve and the noise level generated by the diffuser are the same.
8) Selection of low-noise valve The low-noise valve is used to reduce the velocity of the supersonic flow at any point in the flow path according to the gradual deceleration of the fluid through the spiral flow path (multi-channel, multi-channel) of the valve core and valve seat. There are many types of low-noise valves of various structures (designed for special systems) for use when used. When the noise is not too great, the use of a low-noise sleeve valve can reduce the noise by 10 to 20 decibels, which is the most economical low-noise valve.
Tenth, the solution to the poor stability of the control valve (5 methods)
1) Changing the direction of action of the unbalanced force In the stability analysis, when the unbalanced force is known to be the same as the valve closing direction, that is, when the valve is closed, the valve stability is poor. When the valve is operated under the unbalanced force condition, the method of changing the direction of the action is selected. Usually, the flow-closed type is changed to the flow-opening type. Generally, the valve stability problem can be easily solved.
2) Avoiding valve instability in the working area of ​​the valve itself. Some valves are limited by their own structure and have poor stability when working at certain opening degrees. 1 Double-seat valve, opening within 10%, due to flow at the ball, the flow at the ball off, causing instability; 2 imbalance of the change in the imbalance of the force generated near the alternation, its stability is poor. If the butterfly valve, the alternating point is about 70 degrees; the double seat valve is in the 80-90% opening degree. In the event of such a valve, working in an unstable zone will inevitably have poor stability and avoid working in an unstable zone.
3) Replacing the valve with good stability The valve with good stability has a small change in the unbalanced force and is well guided. Commonly used ball valve, sleeve valve has this great feature. When the stability of the single and double seat valves is poor, the stability of the replacement sleeve valve will surely be improved.
4) The ability of the spring stiffness actuator to resist the impact of load changes on the stroke depends on the spring stiffness. The greater the stiffness, the smaller the influence on the stroke and the better the valve stability. Increasing the spring rate is a common and simple way to improve the stability of the valve. For example, changing the spring range from 20 to 100 KPa to a large stiffness spring between 60 and 180 KPa, this method is mainly used with the valve of the positioner, otherwise, it is used. The valve should be equipped with a locator.
5) Decrease the response speed When the system requires the regulating valve to respond or adjust the speed should not be too fast, the valve response and regulation speed is faster, such as the flow needs to be fine-tuned, but the flow adjustment of the regulating valve is very large, or The system itself is already a quick response to the system while the regulator valve has a positioner to accelerate the valve action, which is all unfavorable. This will produce overshoots, vibrations, etc. In this regard, response speed should be reduced. The methods are: 1 change the linear characteristic to logarithmic characteristic; 2 can be changed to the converter and relay with the positioner.
4) Symmetrically screwed bolts, using thin gasket sealing method In the “O†ring-sealed regulating valve structure, when a thick gasket with large deformation (such as a wound sheet) is used, if the compression is asymmetric, the stress is not symmetrical. , It is easy to damage, tilt and deform the seal, which seriously affects the sealing performance. Therefore, in the maintenance and assembly of such valves, the compression bolts must be tightened symmetrically (be careful not to tighten them once). Thick gaskets are better if they can be changed to thin gaskets, which makes it easier to reduce the slope and ensure the seal.
5) The method of increasing the width of the sealing surface to prevent the flat valve core from jumping and reducing the leakage when it closes The flat plate type valve core (such as the valve plug of the two-way valve and the sleeve valve) has no guide and guide surface in the valve seat When the valve is working, the spool is subjected to a lateral force and flows from the flow-in side to the outflow side. The larger the clearance between the spools, the more serious the unilateral phenomenon is, and the deformation, the misalignment, or the sealing surface of the valve core is reversed. The corner is small (usually 30° chamfer to guide), so when close to close, the chamfered end surface of the sealing surface of the valve core is placed on the sealing surface of the valve seat, causing the valve core to jump when closing, or even not closing the position, so that the valve The amount of leakage has greatly increased. The simplest and most effective solution is to increase the size of the sealing surface of the valve plug so that the minimum diameter of the end face of the valve plug is smaller than the diameter of the valve seat by 1 to 5 mm, and there is enough guiding action to ensure that the valve plug is guided into the valve seat. Good sealing surface contact.
6) Change the direction of flow, solve the problem of promotion, and eliminate the surge method The two-way valve is usually used as a closed flow type to improve the cutting effect. For the liquid medium, due to the effect of the flow-closed unbalanced force, the valve core is closed and the closing effect is promoted, which is also called the suction action. This speeds up the movement speed of the valve core, generates a slight water hammer, and causes the system to surge. The solution to the above phenomenon is to simply eliminate the flow by changing the flow direction. Similar problems such as the fact that the valve does not work properly due to the promotion of clearance can also be considered to take this approach.
7) The most typical valve for overcoming the fluid damage method is a double seat valve. The fluid enters from the middle and the valve core is perpendicular to the inlet. The fluid bypasses the valve core and is divided into upper and lower two bundles. The fluid impinges on the spool, causing it to lean against the outlet side, causing friction and damaging the guide surface of the spool and bushing, causing erratic movements. High flow rates may also cause the spool to bend, erode, and severely break. The solution is: 1 to increase the hardness of the guide site material; 2 to increase the middle size of the valve ball up and down to make it rough; 3 use other valve alternatives. If a sleeve valve is used, fluid flows from around the sleeve and the lateral thrust on the valve plug is greatly reduced.
8) Overcoming the rotational force generated by the fluid to make the valve core rotate. For the valve core of the “V†shape, due to the asymmetry of the medium flow, the tangential force of the valve core acting on the “V†shape is inconsistent, resulting in a Rotating rotational force. In particular, valves with DN ≥ 100 are more intense. As a result, the valve may be disengaged from the actuator stem linkage, and the springless actuator may cause the diaphragm to twist. The solutions include: 1 Turn the valve counter-rotation direction to an angle to balance the tangential force acting on the valve plug; 2 Further lock the connection between the valve stem and the push rod, if necessary, add a piece of anti-rotation clamp; 3 Replace the "V" shaped spool with a plunger-type spool; 4 Use or change to a sleeve-type structure; 5 If the resonance is caused by the rotation, eliminate the resonance to solve the problem.
9) Adjust the friction force of the butterfly valve plate, overcome the open-bounce method and adopt the soft sealed butterfly valve such as “O†ring, seal ring and lining. When the valve is closed, due to the deformation of the soft seal, the valve plate is closed in position and the valve is enclosed. The board can achieve a very good cutting effect. However, when the valve is to be opened, the force of the actuator to open the valve plate is continuously increased. When the frictional force of the soft seal to the valve plate is equal, the valve plate starts. Once started, this friction force decreases dramatically. In order to achieve the balance of force, the valve plate opens violently. When this force is balanced with the unbalance torque of the corresponding opening medium and the opening moment of the actuator, the valve stops at this opening. This violent and sudden jump opens up to 30 to 50%, which will create a series of problems. At the same time, due to the soft seal to produce a large change when closed, easy to produce permanent deformation or by the valve plate, such as damage, strain, affect the life. The solution is to adjust the frictional force of the soft seal against the start of the valve plate, which can not only meet the required cutting requirements, but also make the valve start more normally. Specific measures include: 1 adjustment of the amount of interference; 2 limit or adjust the pre-tightening force of the implementing agencies, the output force approach to reduce the excessive closure of the valve plate to open the difficulties.
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