Introduction to common troubleshooting methods for regulating valves

In industrial automation instruments, the regulating valve is cumbersome, and the structure is simple, and it is often not taken seriously. However, it has complicated working conditions on the process pipeline, and once there is a problem, everyone is busy. Because of its cumbersomeness, the problem is difficult to find, often it is difficult to please, but also involves system commissioning, system completeness, quality adjustment, environmental pollution.
First, ways to improve life (8 methods)
1) Extended working life extension method
Let the regulator work as far as possible at the maximum opening, such as 90%. Thus, cavitation, erosion, and the like occur on the head of the spool. As the spool is broken, the flow rate increases, and the corresponding valve is closed again. This is continuously destroyed and gradually closed, so that the entire spool is fully utilized until the root of the spool and the sealing surface are broken and cannot be used. At the same time, the large opening degree of the throttle opening is large, and the erosion is weakened. This makes the valve work at the intermediate opening degree and the small opening degree to increase the service life by 1 to 5 times than at the beginning. If a chemical plant adopts this method, the service life of the valve is increased by 2 times.
2) Reduce S to increase the working opening and improve the life method
Decrease S, that is, increase 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 rate passes through the regulating valve, the opening degree of the regulating valve is inevitably increased, and at the same time, the pressure drop on the valve is reduced, so that Cavitation and erosion are also weakened. The specific methods include: the orifice pressure consumption of the orifice plate after the valve is used; the manual valve connected in series on the pipeline is closed, and the valve is obtained to obtain a better working opening degree. This method is very simple, convenient and effective when the valve selection is at a small opening.
3) Reduce the caliber to increase the working opening and improve the life method
By increasing the diameter of the valve to increase the working opening, the specific methods are: 1 change a small first-diameter valve, such as DN32 to DN25; 2 valve body does not change, replace the small valve seat diameter spool valve seat. If a chemical plant is overhauled, the throttle dgl0 is replaced with dg8, and the life is increased by one time.
4) Transfer damage location to improve life method
Transfer the severely damaged area to a secondary location to protect the sealing and throttling surfaces of the valve seat.
5) Growth throttling channel to improve life method
The simplest way to increase the throttling channel is to thicken the seat to increase the seat bore and create a longer throttling channel. On the one hand, the sudden expansion of the flow-closed throttling can be postponed, and the position of the transfer can be shifted away from the sealing surface; on the other hand, the throttling resistance is increased, the degree of recovery of the pressure is reduced, and the steam is reduced. The erosion is weakened. Some design the valve seat hole as a stepped, wave type, in order to increase the resistance and reduce the cavitation. This method is often used when introducing high pressure valves in the installation and retrofitting old valves, and is also very effective.
6) Change the flow direction to improve the life method
The flow-opening type flows toward the opening direction, and the cavitation and erosion mainly act on the sealing surface, so that the sealing surface of the valve core and the valve seat is quickly damaged; the flow-closing type flows toward the closed direction, cavitation and erosion. After throttling, below the seat sealing surface, the sealing surface and the root of the valve plug are protected, extending life. Therefore, when the valve for the flow-open type is used, when the problem of prolonging the life is more prominent, the life can be extended by one to two times by simply changing the flow direction.
7) Use special materials to improve life method
In order to resist cavitation (destruction of shapes such as honeycomb dots) and scouring (streamlined small grooves), special materials resistant to cavitation and erosion can be used to manufacture the throttle. This special material is 6YC-1, A4 steel, stellite, hard alloy and so on. For corrosion resistance, materials that are more resistant to corrosion and have certain mechanical and physical properties can be used. This material is divided into non-metallic materials (such as rubber, PTFE, ceramics, etc.) and metal materials (such as Monel, Hastelloy, etc.).
8) Change the valve structure to improve the life method
The purpose of improving the life is achieved by changing the valve structure or using a valve with a longer life, such as a multi-stage valve, an anti-cavitation valve, a corrosion-resistant valve, and the like.
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 are blocked or jammed in the orifice, the guiding part and the balance hole of the lower bonnet, causing strain and scratches on the curved surface of the valve core, the guiding surface, and indentation on the sealing surface. Wait. This often happens in the early stages of the new commissioning system and after the overhaul. This is the most common failure. 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 is opened to wash off the slag falling into the lower bonnet from the balance hole, and the pipeline Rinse. Before commissioning, let the regulating valve open completely, and the medium will flow into the normal operation after a period of time.
2) External scouring method
When some media that are easy to precipitate and contain solid particles are adjusted by ordinary valves, they are often blocked at the throttle and guide, and the gas and steam can be flushed at the bottom of the lower bonnet. When the valve is blocked or jammed, open the external gas or steam valve to complete the flushing operation without moving the regulating valve to make the valve operate normally.
3) Installation of the pipe filter method
For small-diameter regulating valves, especially ultra-small flow regulating valves, the throttle gap is very small, and there should be no slag in the medium. In case of blockage, it is best to install a filter on the pipe in front of the valve to ensure the smooth passage of the media. With the regulating valve used by the positioner, the positioner does not work properly, and the blockage of the air passage throttle is the most common fault. Therefore, when working with the positioner, the air source must be handled. The usual method is to install an air filter pressure reducing valve on the air supply line before the positioner.
4) Increase the throttling gap method
If the solid particles in the medium or the slag and rust that are washed away in the pipeline cannot be blocked or jammed due to the throttle opening, the throttle with a large throttle gap can be used instead. Valves and sleeves of windows and openings can be easily eliminated because their throttle areas are concentrated rather than circumferentially distributed. If it is a single or double seat valve, the plunger valve core can be changed to a "V" shaped valve core, or changed to a sleeve valve. For example, if a chemical plant has a double seat valve that is often stuck, it is recommended to use the sleeve valve to solve the problem immediately.
5) Medium scouring method
Using the scouring energy of the medium itself, scouring and taking away things that are easy to precipitate and easily clog, thereby improving the anti-blocking function of the valve. Common methods are: 1 changed to flow-type use; 2 uses streamlined valve body; 3 puts the throttle port to the most powerful part of the flushing, and this method should pay attention to improve the erosion resistance of the material of the throttle piece. 6) Straight through to the angle method
The straight-through flow is inverted S, the flow path is complicated, and there are many dead zones in the upper and lower chambers, which provide a place for the precipitation of the medium. The angular connection, the medium is like flowing through the 90 °C elbow, the scouring performance is good, the dead zone is small, and it is easy to design into a streamline shape. Therefore, the use of a straight-through regulating valve can be changed to an angle valve when it is slightly blocked.
Third, the solution to the regulation valve leakage (6 methods)
1) Increase the sealing grease method
For valves that do not use seal grease, consider adding seal grease to improve stem seal performance.
2) Add filler method
In order to improve the sealing performance of the filler to the valve stem, a method of increasing the filler may be employed. Usually it is a double-layered, multi-layered mixed filler form, which simply increases the number. For example, if you increase 3 pieces to 5 pieces, the effect is not obvious.
3) Replacement of graphite filler method
The PTFE filler used in a large amount has a working temperature of -20 to +200 ° C. When the temperature is changed at the upper and lower limits, the sealing property is obviously lowered, the aging is fast, and the life is short. Flexible graphite fillers overcome these shortcomings and have a long service life. Therefore, some factories have changed the PTFE filler to graphite filler, and even the newly purchased regulator valve has replaced the PTFE filler with graphite filler. However, the use of graphite fillers has a large backlash, and some of them also have creeping phenomenon at the beginning, which must be considered.
4) Change the flow direction, set P2 at the stem end method
When ΔP 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, and P1 is changed at the valve stem end to P2 at the valve stem end, which is more effective for a valve having a high pressure and a large differential pressure. For example, bellows valves should normally consider sealing P2.
5) Using the lens pad sealing method
For the sealing of the upper and lower covers, the valve seat is sealed with the upper and lower valve bodies. If it is a flat seal, under high temperature and high pressure, the sealing performance is poor, causing leakage, and the lens pad seal can be used instead, and satisfactory results can be obtained.
6) Replace the gasket
Up to now, most of the sealing gaskets still use asbestos sheets. At high temperatures, the sealing performance is poor and the service life is short, causing leakage. In this case, you can use a wound gasket, an "O" ring, etc., which is now used in many factories.
Fourth, the solution to the vibration of the regulating valve (8 methods)
1) Increase the stiffness method
For oscillation and slight vibration, the stiffness can be increased to eliminate or weaken. For example, it is feasible to use a spring with a large stiffness and a piston actuator.
2) Increase the damping method
Increasing the damping increases the friction against vibration. For example, the valve plug of the sleeve valve can be sealed with an “O” ring, and a graphite filler with a large friction force can be used to eliminate or attenuate slight vibration.
3) Increase the guide size and reduce the fit clearance method
Shaft plug valves generally have small guide sizes, and all valve fit clearances are generally large, 0.4 to 1 mm, which is helpful for generating mechanical vibration. Therefore, when a slight mechanical vibration occurs, the vibration can be weakened by increasing the guide size and reducing the fit clearance.
4) Change the shape of the throttle to eliminate the resonance method
Since the so-called vibration source of the regulating valve occurs at the throttle port with high-speed flow and rapid pressure change, changing the shape of the throttle member can change the frequency of the vibration source, and it is easier to solve when the resonance is not strong. The specific method is to turn the valve core surface by 0.5 to 1.0 mm in the range of vibration opening. For example, if a self-operated pressure regulating valve is installed near a certain manufacturer's area, the whistling of the resonance will affect the rest of the staff. After the valve core is turned off by 0.5mm, the resonance whistling sound disappears.
5) Replace the throttle to eliminate the resonance method
The methods include: 1 changing the flow characteristics, linearly changing the logarithm, linearly changing the logarithm; 2 replacing the spool form. If the shaft plug shape is changed to a "V"-shaped groove valve core, the double seat valve shaft plug type is changed into a sleeve type; the open window sleeve is changed to a small hole sleeve. For example, if a DN25 double seat valve of a nitrogen fertilizer plant, the connection between the valve stem and the valve core is often broken, we confirm that after resonance, the linear characteristic valve core is changed to a logarithmic valve core, and the problem is solved. Another example is the use of a DN200 sleeve valve in an aeronautical laboratory. The valve plug is strongly rotated and cannot be used. When the sleeve of the open window is changed to the sleeve of the small hole, the rotation disappears immediately.
6) Replace the regulator type to eliminate resonance.
Different types of regulating valves have different natural frequencies, and replacing the regulating valve type is the most effective way to fundamentally eliminate resonance. A valve resonates very strongly in use—strongly vibrating (destroying the valve in severe cases), rotating strongly (even the stem is broken, twisted), and producing strong noise (up to 100 decibels) The valve, as long as it is replaced by a valve with a large difference in structure, immediately works, and the strong resonance disappears miraculously. For example, a new DN200 sleeve valve is selected for the new expansion project of a Vinylon plant. The above three phenomena exist. The DN300 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 opening. When the degree is large, after switching to a double seat valve, the resonance disappears and the operation is normal.
7) Reduce the cavitation vibration method
For cavitation vibrations caused by cavitation bubble collapse, 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 on the valve core, but allows the liquid to absorb. The sleeve valve has this feature, so the plug type spool can be changed to a sleeve type. 2 Take all measures to reduce cavitation, such as increasing throttling resistance, increasing the pressure at the contraction port, decompression in series or series.
8) Avoid the source wave strike method
External vibration source wave shock causes valve vibration, which is obviously avoided when the regulating valve works normally. If such vibration is generated, corresponding measures should be taken.
Fifth, the solution to the noise of the regulating valve (8 methods)
1) Elimination of resonance noise method
Only when the regulating valve resonates, there is energy superposition that produces a strong noise of more than 100 decibels. Some performances are strong vibration, low noise, some vibrations are weak, and the noise is very large; some vibrations and noise are large. This noise produces a single-tone sound that typically has a frequency of 3000 to 7000 Hz. Obviously, the resonance is eliminated and the noise naturally disappears.
2) Elimination of cavitation noise method
Cavitation is the main source of hydrodynamic noise. At the time of cavitation, the bubble burst produces a high-speed impact, causing strong turbulence locally, resulting in cavitation noise. This noise has a wide frequency range that produces a gig sound similar to that of a fluid containing sand. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
3) Using thick-walled pipeline method
The use of thick-walled tubes is one of the sound path treatment methods. The use of thin walls increases noise by 5 decibels, and the use of thick-walled tubes reduces noise by 0 to 20 decibels. The thicker the same pipe diameter, the larger the pipe diameter of the same wall, the better the noise reduction effect. For example, when the wall thickness of DN200 pipe is 6.25, 6.75, 8, 10, 12.5, 15, 18, 20, 21.5mm, the noise can be reduced to -3.5, -2 (ie increase), 0, 3, 6, respectively. 8, 11, 13, 14.5 decibels. Of course, the thicker the wall, the higher the cost.
Sixth, the solution to the vibration of the regulating valve (8 methods)
1) Increase the stiffness method
For oscillation and slight vibration, the stiffness can be increased to eliminate or weaken. For example, it is feasible to use a spring with a large stiffness and a piston actuator.
2) Increase the damping method
Increasing the damping increases the friction against vibration. For example, the valve plug of the sleeve valve can be sealed with an “O” ring, and a graphite filler with a large friction force can be used to eliminate or attenuate slight vibration.
3) Increase the guide size and reduce the fit clearance method
Shaft plug valves generally have small guide sizes, and all valve fit clearances are generally large, 0.4 to 1 mm, which is helpful for generating mechanical vibration. Therefore, when a slight mechanical vibration occurs, the vibration can be weakened by increasing the guide size and reducing the fit clearance.
4) Change the shape of the throttle to eliminate the resonance method
Since the so-called vibration source of the regulating valve occurs at the throttle port with high-speed flow and rapid pressure change, changing the shape of the throttle member can change the frequency of the vibration source, and it is easier to solve when the resonance is not strong. The specific method is to turn the valve core surface by 0.5 to 1.0 mm in the range of vibration opening. For example, if a self-operated pressure regulating valve is installed near a certain manufacturer's area, the whistling of the resonance will affect the rest of the staff. After the valve core is turned off by 0.5mm, the resonance whistling sound disappears.
5) Replace the throttle to eliminate the resonance method
The principle is the same as 4 in 4.5, except that the throttle is replaced. The methods include: 1 changing the flow characteristics, linearly changing the logarithm, linearly changing the logarithm; 2 replacing the spool form. If the shaft plug shape is changed to a "V"-shaped groove valve core, the double seat valve shaft plug type is changed into a sleeve type; the open window sleeve is changed to a small hole sleeve. For example, if a DN25 double seat valve of a nitrogen fertilizer plant, the connection between the valve stem and the valve core is often broken, we confirm that after resonance, the linear characteristic valve core is changed to logarithm