This common valve failure? I have 50 tips!
The valve is only a small role in the factory, but once the failure, the impact is not small. In particular, regulating valves are relatively bulky in the valves. Therefore, in the event of a failure, the problem is difficult to identify, and often it is laborious and thankless.
Today, we have brought about 50 ways to solve the fault of the regulating valve. Let’s take a look!
When a fault occurs, which parts should be checked?
1 valve body wall
For regulating valves used in high pressure differential and corrosive media applications, the inner wall of the valve is often subjected to the impact and corrosion of the medium. It is necessary to check the pressure resistance and corrosion resistance.
When the regulating valve is working, the inner surface of the thread used for fixing the valve seat is susceptible to corrosion and the valve seat is loosened due to the infiltration of the medium. Attention should be paid when checking. For valves operating under high differential pressure, check also whether the sealing surface of the valve seat is damaged.
The valve core is a movable part when the regulating valve is working. It is corroded by the medium, and the corrosion is the most serious. When the inspection is performed, it is necessary to check whether the various parts of the valve core are corroded and worn. Especially when the high pressure difference is bad, the valve core wears more seriously. , (due to cavitation) should be noted. If the valve core is badly damaged, it should be replaced. In addition, it should also pay attention to whether the stem has a similar phenomenon, or loose connection with the spool.
4 “O” seals and other gaskets
Whether aging, cracking.
5 PTFE packing, sealed grease
Whether aging, whether the mating surface is damaged, should be replaced when necessary.
What happens when the valve leaks?
1 increase the sealing grease
For valves that do not use sealed grease, consider adding sealant grease to improve stem seal performance.
2 increase filler
In order to improve the sealing performance of the packing on the stem, a method of increasing the filling may be used. Usually double-layered or multi-layered mixed fillers are used. Simply increasing the number, such as increasing 3 to 5, is not effective.
3 replacement graphite filler
The PTFE filler used in large quantities, because of its working temperature in the range of -20 ~ +200 °C, when the temperature in the upper and lower limits, a large change, the sealability will be significantly reduced, aging fast, short life.
Flexible graphite fillers overcome these drawbacks 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 flow, set P2 on the stem side
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. The P1 is changed from the stem end to the P2 end of the stem, which is more effective for valves with high pressure and large pressure difference. For example, the bellows valve should normally be considered sealed P2.
5 using a lens pad seal
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 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 gasket
To date, most gaskets still use asbestos plates, which have poor sealing performance and short life at high temperatures, causing leakage. In this case, wound gaskets, “O” rings, etc., can be used instead, and many plants have already adopted them.
7 symmetrical bolts, sealed with a thin gasket
In the “O”-shaped ring seal adjustment valve structure, when a thick gasket with a large deformation (such as a wound sheet) is used, if the pressure is asymmetric and the stress is not symmetrical, the seal is easily damaged, tilted, and deformed. Seriously affect 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, so that it is easy to reduce the slope and ensure the seal.
8 increase the sealing surface width
Plate-type valve plugs (such as the valve plug of two-way valve and sleeve valve) have no guide and guide surface in the valve seat. Because the valve is working, the valve core is subjected to lateral force and flows from the flow inlet to the outlet. The larger the clearance between the plug and the valve core, the more serious the unilateral phenomenon is, combined with deformation, misalignment, or a small chamfer on the sealing surface of the valve plug (usually a 30° chamfer to guide), so that when the valve plug closes, the valve plug seals. The chamfered end face is placed on the sealing surface of the valve seat, causing the valve core to jump when closing, or even shutting off the position in a non-standard manner, so that the leakage amount of the valve is 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.
Adjust valve vibration, how to solve?
1 increase the stiffness
For oscillation and slight vibration, the rigidity can be increased to eliminate or weaken. For example, selecting a spring with a large rigidity and using a piston actuator is feasible.
2 Increase damping
Increasing the damping means increasing the friction to the vibration. For example, the valve plug of the sleeve valve can be sealed with an “O” ring, and the graphite filler with a large friction force is used, which still plays a role in eliminating or reducing the slight vibration.
3 increase the guide size, reduce the fit gap
Shaft-shaped valves generally have smaller guide dimensions, and all valves have generally larger clearances of 0.4 to 1 mm, which is helpful for generating mechanical vibrations. 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 throttle to eliminate resonance
Because the so-called vibration source of the regulating valve occurs in the throttle opening where high-speed flow and rapid pressure change occur, the frequency of the vibration source can be changed by changing the shape of the throttle, and it is relatively easy to solve when the resonance is not strong.
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 has installed a self-operated pressure regulating valve near the company’s property area, the resonance generated a whistle and affected the worker’s rest. After the 0.5 mm displacement of the slider surface, the resonance whistling noise disappeared.
5 Replace the throttle to eliminate resonance
Its methods are:
Change the flow characteristics, change the logarithm to linear, change the logarithm linearly;
Replace the spool form. If the plug shape is replaced by a “V” shaped valve spool, the double seat valve plug type is changed to a sleeve type;
Change the sleeve that opens the window to a sleeve that makes a small hole.
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 Reduction of cavitation vibration
In the case of cavitational vibrations due to the collapse of cavitation bubbles, it is natural to find ways to reduce cavitation.
The impact energy generated by the collapse of the bubble does not act on the solid surface, especially the valve plug, but rather 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.
Take all the measures to reduce cavitation, such as increasing throttling resistance, increasing the pressure of the reducing orifice, grading or decompression in series.
7 Avoid vibration source wave attack
The vibration of the valve caused by the vibration of the external source is obviously avoided when the control valve works normally. If such vibration occurs, corresponding measures should be taken.
Regulator valve noise, how to do?
1 eliminate resonance noise
Only when the control valve resonates, can there be superimposed energy and produce a loud 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.
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 Use thick-walled pipelines
The use of thick-walled pipelines 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 (that is, increase), 0,3,6, 8,11,13,14.5 dB. Of course, the thicker the wall, the higher the cost.
4 using sound-absorbing materials
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 noise elimination 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 series silencer
This method is applicable to the silencing of aerodynamic noise, 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 economical point of view, it is generally limited to attenuation of about 25 dB.
6 soundproof box
Noise barriers, houses, and buildings are used to isolate the noise sources so that the noise of the external environment can be reduced to an acceptable level.
7 series throttle
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 on 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 use low noise valve
The low-noise valve gradually decelerates according to the flow path of the fluid passing through the valve core and valve seat (multi-channel, multi-channel) to avoid generating supersonic velocity at any point in the flow path. There are many types of low-noise valves of various structures (designed for special systems) for use when used.
When the noise is not very large, the use of a low-noise sleeve valve can reduce the noise by 10 to 20 dB, which is the most economical low-noise valve.
Valve blockage, how to prevent?
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. Dross is removed. If the sealing surface is damaged, it should be ground. At the same time, the bottom plug should be opened to flush the slag falling 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, and the flushing work can be completed without the regulating valve, so that the valve can operate normally.
3 Install the pipe filter
For the small-diameter control valve, especially the ultra-small flow control valve, the throttling clearance is very small, and 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 fault.
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
If the solid granules in the medium or the slag and rust that has been washed out of the pipe, etc., cannot be blocked or stuck due to the throttle opening, the throttling device with a large throttling gap can 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 wash method
Using the media’s own flushing energy, it can scour and carry away the easy-to-precipitate, easy-to-clog and increase the anti-blocking function of the valve.
Common methods are:
Change to flow closed type use;
The throttling orifice is placed in the most erosive position. This method should be used to increase the erosion resistance of the throttling material.
6 straight through to angle
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.
Regulator valve poor stability, how to do?
1 Change the direction of action of imbalance force
In the stability analysis, when the effect of the known unbalanced force is 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 above-mentioned unbalanced force conditions, the method of changing the direction of its 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 to avoid the work of the valve itself unstable area
Some valves are limited by their own structure and have poor stability when working at certain opening degrees.
Double-seat valve, opening within 10%, due to flow at the ball, the flow at the ball off, causing instability; imbalance changes in the slope 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 Replace the valve with good stability
Valves with good stability have a small change in imbalance force and good guidance. The 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 certainly be improved.
4 increase the spring rate
The ability of the actuator to resist the impact of load changes on the stroke depends on the stiffness of the spring. The greater the stiffness, the smaller the effect on the stroke and the better the stability of the valve.
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 response speed
When the system requires the regulating valve to respond or the regulating speed should not be too fast, the valve responds and adjusts the speed quickly, such as the flow needs to be fine-tuned, and the regulating flow rate of the regulating valve varies greatly, or the system itself is already rapidly responding. The system and the regulating valve but with the positioner to accelerate the valve action are both disadvantageous.
This will produce overshoots, vibrations, etc. In this regard, response speed should be reduced.
Change the linear characteristics to logarithmic characteristics;
With a locator can be changed to a converter, following
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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