Description
Z7126 Germany HIMA
Z7126 Germany HIMA
Module Clips Drive controller servo motor
Contact: Mr. Lai
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In industrial automation instruments, the regulating valve is relatively bulky and simple in structure, which is often ignored by people. However, the working conditions of the regulating valve on the process pipeline are complex, and once there are problems, everyone is busy with their hands and feet. Due to its cumbersome nature, it is difficult to pinpoint problems, often laborious and thankless, and also involves system operation, system completeness, quality regulation, environmental pollution, etc. This article summarizes 47 methods that are sufficient for everyone to solve seven common on-site problems, including valve lifespan, valve blockage, valve leakage, valve vibration, high valve noise, and valve vibration.
1、 Eight Methods to Improve the Service Life of Regulating Valves Z7126 Germany HIMA
1. Method of Extending the Life of Regulating Valves by Working with Large Opening
Let the regulating valve work at its maximum opening from the beginning, such as 90%. In this way, damage such as cavitation and erosion occurs on the valve core head. As the valve core is damaged and the flow rate increases, the corresponding valve is closed a little more. This continues to damage and gradually closes, making the entire valve core fully utilized until the root and sealing surface of the valve core are damaged and cannot be used. At the same time, the large opening work has a large throttle clearance and weakened erosion, which increases the service life of the valve by more than 1-5 times compared to working at the middle and small opening from the beginning. If a certain chemical plant adopts this method, the service life of the regulating valve has been increased by two times.
2. Reducing S and increasing working opening to improve service life method
Reducing S means increasing the loss of the system except for the regulating valve, reducing the pressure drop distributed to the valve. To ensure that the flow passes through the regulating valve, the opening of the regulating valve must be increased. At the same time, the pressure drop on the valve decreases, weakening cavitation and erosion. The specific methods include: setting an orifice plate behind the valve to throttle and consume pressure drop; Close the manual valves connected in series on the pipeline until the regulating valve achieves an ideal working opening. This method is very simple, convenient, and effective when selecting a large valve and working with a small opening at the beginning.
3. Reducing the aperture, increasing the working opening, and improving the service life method
By reducing the valve diameter to increase the working opening, the specific methods are:
① Change to a valve with a smaller caliber, such as DN25 instead of DN32; Z7126 Germany HIMA
② The valve body remains unchanged, replace the valve core and valve seat with a small valve seat diameter. During a major overhaul of a chemical plant, the throttling component DN1000 was replaced with DN80, which doubled the service life.
4. Method of Transferring Damaged Positions to Improve the Service Life of Regulating Valves
Transfer the severely damaged area to a secondary location to protect the sealing and throttling surfaces of the valve core and seat.
5. Method of Increasing the Throttling Channel and Improving the Service Life of Regulating Valves
The simplest way to increase the throttling channel is to thicken the valve seat, causing the valve seat hole to grow, forming a longer throttling channel. On the one hand, it can cause the sudden expansion and delay of the flow closed throttle, which plays a role in transferring the damaged position and keeping it away from the sealing surface; On the other hand, it also increases throttling resistance, reduces the degree of pressure recovery, and weakens cavitation. Some design the valve seat hole as a stepped or wavy shape to increase resistance and weaken cavitation. This method is often used on high-pressure valves in imported devices and when improving old valves, and is also very effective.
6. Method of changing flow direction to improve the service life of regulating valves
The flow opening type flows towards the open direction, and cavitation and erosion mainly act on the sealing surface, causing damage to the valve core root and valve seat sealing surface quickly; The flow closed type flows towards the closed direction, and cavitation and erosion act below the sealing surface of the valve seat after throttling, protecting the sealing surface and the root of the valve core, and extending its service life. When the problem of extending the service life of a valve used in a flow open type is prominent, simply changing the flow direction can extend the service life by 1-2 times.
7. Method of using special materials to increase the service life of regulating valves
To resist cavitation (such as honeycomb shaped small points) and erosion (streamlined small grooves), special materials that resist cavitation and erosion can be used to manufacture throttling components. This special material includes 6YC-1, A4 steel, Stellite, hard alloy, etc. To resist corrosion, materials that are more resistant to corrosion and have certain mechanical and physical properties can be used instead. This material is divided into two categories: non-metallic materials (such as rubber, PTFE, ceramics, etc.) and metallic materials (such as Monel, Hastelloy, etc.).
8. Method of changing valve structure to improve service life
By changing the valve structure or selecting valves with longer service life, the goal of improving service life can be achieved, such as selecting multi-stage valves, anti cavitation valves, corrosion-resistant valves, etc.
2、 Six methods to prevent blockage (jamming) of regulating valves that often get stuck or blocked
1. Cleaning method
Welding slag, rust, slag, etc. in the pipeline cause blockage or jamming in the throttle port, guide part, and balance hole of the lower valve cover, resulting in scratches and scratches on the valve core surface and guide surface, as well as pressure marks on the sealing surface. This often occurs in the early stages of new systems being put into operation and after major repairs. This is the most common malfunction. In this case, it must be disassembled and cleaned to remove debris. If the sealing surface is damaged, it should also be ground; At the same time, open the bottom plug to flush out any debris that falls into the lower valve cover from the balance hole, and flush the pipeline. Before putting into operation, allow the regulating valve to fully open and allow the medium to flow for a period of time before being brought into normal operation.
2. External scouring method
When using ordinary valves to regulate media that are prone to sedimentation and contain solid particles, they often block the throttle and guide ports, and can be externally connected with flushing gas and steam at the bottom plug of the lower valve cover. When the valve becomes blocked or stuck, opening the external gas or steam valve can complete the flushing work without moving the regulating valve, ensuring the normal operation of the valve.
3. Installation of pipeline filter method
For small caliber control valves, especially ultra small flow control valves, their throttling clearance is particularly small, and there should be no small residue in the medium. In case of blockage in this situation, it is best to install a filter on the pipeline in front of the valve to ensure the smooth passage of the medium. The most common malfunction of a regulating valve with a locator is that the locator is not working properly and its gas path throttle is blocked. Therefore, when working with a locator, it is necessary to handle the air source properly. The usual method is to install an air filter pressure reducing valve on the air source pipeline in front of the locator.
4. Increase throttle clearance method
If solid particles in the medium or welding slag and rust that have been washed away in the pipeline cannot pass through the throttling port, causing blockages, blockages, and other faults, they can be replaced with throttling components with large throttling gaps – valve cores and sleeves with window or opening areas. Due to their concentrated throttling area rather than circular distribution, the fault can be easily eliminated. If it is a single or double seat valve, the plunger shaped valve core can be changed to a “V” shaped valve core, or to a sleeve valve. For example, a double seat valve in a chemical factory often gets stuck, and it is recommended to use a sleeve valve as soon as the problem is solved.
5. Medium erosion method
Utilize the scouring energy of the medium itself to flush and remove easily precipitated and clogged substances, thereby improving the anti clogging function of the valve. Common methods include:
① Change to flow closed type use;
② Adopting a streamlined valve body;
③ Place the throttle at the point where the erosion is most severe. When using this method, attention should be paid to improving the erosion resistance of the throttle material.
6. Change direct to angular method
The direct flow is an inverted S flow, with complex flow paths and multiple dead zones in the upper and lower chambers, providing a place for the precipitation of the medium. Angular connection, the medium is like flowing through a 90 ℃ elbow, with good erosion performance, small dead zone, and easy to design as a streamline. Therefore, when using a straight through regulating valve that causes slight blockage, it can be changed to an angle valve for use.
3、 Six methods to solve the leakage of regulating valves
1. Add sealing grease method
For valves that do not use sealing grease, adding sealing grease can be considered to improve the sealing performance of the valve stem.
2. Adding filler method
To improve the sealing performance of the packing on the valve stem, the method of adding packing can be adopted. Usually, double or multi-layer mixed fillers are used, and simply increasing the quantity, such as increasing 3 to 5 pieces, does not have a significant effect.
3. Replacing graphite packing method
The widely used tetrafluoro filler, due to its working temperature range of -20~+200 ℃, significantly reduces its sealing performance, aging quickly, and has a short lifespan when the temperature changes significantly between the upper and lower limits. Flexible graphite fillers can overcome these shortcomings and have a long service life. Therefore, some factories have completely changed the PTFE packing to graphite packing, and even newly purchased control valves have replaced the PTFE packing with graphite packing for use. However, the use of graphite fillers has a large return difference, and some may even experience crawling at the beginning, which must be taken into account.
4. Change the flow direction and place P2 at the valve stem end
When Δ P is large and P1 is also large, sealing P1 is clearly more difficult than sealing P2. Therefore, the method of changing the flow direction can be adopted, changing P1 from P2 at the valve stem end to P2 at the valve stem end, which is more effective for valves with high pressure and large pressure difference. For bellows valves, sealing P2 should usually be considered.
5. Using lens pad sealing method
For the sealing of the upper and lower covers, the sealing of the valve seat and the upper and lower valve bodies. If it is a flat seal, under high temperature and pressure, the sealing performance is poor, causing leakage. It can be replaced with a lens gasket seal to achieve satisfactory results.
6. Replace the sealing gasket
Until now, most sealing gaskets still use asbestos sheets, which have poor sealing performance and short lifespan at high temperatures, leading to leakage. In this situation, spiral wound gaskets, “O” rings, etc. can be used instead, and many factories have now adopted them.
4、 8 Methods to Solve Vibration of Regulating Valves
1. Increasing stiffness method
For oscillations and slight vibrations, increasing stiffness can be used to eliminate or weaken them, such as selecting springs with high stiffness or switching to piston actuators.
2. Increase damping method
Increasing damping means increasing friction against vibration. For example, the valve plug of a sleeve valve can be sealed with an “O” ring, and graphite packing with high friction can be used. This can still have a certain effect on eliminating or weakening slight vibrations.
3. Increase guide size and reduce fit gap method
The guide size of axial plug valves is generally small, and the clearance between all valves is generally large, ranging from 0.4 to 1mm, which is helpful for generating mechanical vibration. Therefore, when slight mechanical vibration occurs, the vibration can be weakened by increasing the guide size and reducing the fit gap.
4. Change the shape of the throttling element and eliminate resonance method
Because the so-called vibration source of the regulating valve occurs at the throttle port with high-speed flow and rapid pressure changes, changing the shape of the throttle element can change the frequency of the vibration source, which is easier to solve when the resonance is not strong. The specific method is to turn the valve core surface within the range of vibration opening by 0.5-1.0mm. For example, a self operated pressure regulating valve was installed near the family area of a certain factory, and the resonance generated a howling sound that affected employees” rest. After Changhui Instrument lowered the valve core surface by 0.5mm, the resonance howling sound disappeared
5. Replacing throttle components to eliminate resonance method
The methods include:
① Change the flow characteristics, logarithmic to linear, linear to logarithmic;
② Replace the valve core form. If the plug shape of the shaft is changed to “V The “shaped groove valve core” was changed from a double seat valve shaft plug type to a sleeve type, and the sleeve with a window was changed to a sleeve with a small hole. For example, a DN25 double seat valve in a nitrogen fertilizer plant often vibrates and breaks at the connection between the valve stem and the valve core. After Changhui Instrument confirmed resonance, the linear characteristic valve core was changed to a logarithmic valve core, and the problem was solved. Another example is a DN200 sleeve valve used in a laboratory of a certain aviation college, which causes strong rotation of the valve plug and cannot be put into use. Therefore, the sleeve with a window was opened After changing to a sleeve with small holes, the rotation immediately disappears.
6. Replace the type of regulating valve to eliminate resonance
The natural frequencies of regulating valves with different structural forms naturally vary, and changing the type of regulating valve is the most effective method to fundamentally eliminate resonance. A valve that resonates extremely strongly in use – it vibrates strongly (can damage the valve in severe cases), rotates strongly (even the valve stem is broken or twisted), and produces strong noise (up to over 100 decibels). As long as it is replaced with a valve with a significant structural difference, it immediately takes effect, and the strong resonance miraculously disappears. If a DN200 sleeve valve is selected for the new expansion project of a certain Vinylon factory, all three phenomena mentioned above exist. The DN300 pipeline jumps, the valve plug rotates, the noise exceeds 100 decibels, and the resonance opening is 20-70%. Considering the large resonance opening, the resonance disappears after switching to a double seat valve, and the operation is normal.
7. Reducing cavitation vibration method
For the cavitation vibration caused by cavitation bubble rupture, it is natural to find ways to reduce cavitation.
① The impact energy generated by bursting bubbles does not act on the solid surface, especially on the valve core, but is absorbed by the liquid. Sleeve valves have this characteristic, so the plug type valve core can be changed to a sleeve type.
② Take all measures to reduce cavitation, such as increasing throttling resistance, increasing the pressure at the constriction port, grading or series pressure reduction, etc.
8. Avoiding vibration source wave strike method
The vibration of the valve caused by external vibration sources is clearly something that should be avoided during normal operation of the regulating valve. If this vibration occurs, corresponding measures should be taken
5、 8 Methods to Solve High Noise in Regulating Valves
1. Resonance noise elimination method
Only when the regulating valve resonates, there is a strong noise of over 100 decibels generated by energy superposition. Some exhibit strong vibration with minimal noise, while others exhibit weak vibration with very high noise; Some have significant vibrations and noise. This type of noise produces a single tone sound, with a frequency typically ranging from 3000 to 7000 Hz. Obviously, by eliminating resonance, the noise naturally disappears. Methods and examples can be found in the previous examples.
2. Method of eliminating cavitation noise
Cavitation is the main source of hydrodynamic noise. During cavitation, the bubble ruptures and produces high-speed impacts, causing strong turbulence and cavitation noise locally. This type of noise has a wide frequency range and produces a grating sound, similar to the sound emitted by fluids containing sand and gravel. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
3. Using thick wall pipeline method
One of the methods for acoustic path treatment is to use thick walled pipes. The use of thin-walled pipes can increase noise by 5 decibels, while the use of thick walled pipes can reduce noise by 0-20 decibels. The thicker the wall of the same pipe diameter, the larger the pipe diameter of the same wall thickness, and the better the noise reduction effect. When the wall thicknesses of DN200 pipes are 6.25, 6.75, 8, 10, 12.5, 15, 18, 20, and 21.5mm, the noise can be reduced by -3.5, -2 (i.e. increased), 0, 3, 6, 8, 11, 13, and 14.5 decibels, respectively. Of course, the thicker the wall, the higher the cost.
4. Using sound-absorbing material method
This is also a common and most effective sound path processing method. Sound absorbing materials can be used to wrap the noise source and the pipeline behind the valve. It must be pointed out that since noise can propagate over long distances through fluid flow, the effectiveness of noise reduction ends wherever the sound-absorbing material is packaged and thick walled pipes are used. This method is suitable for situations where the noise is not very high and the pipeline is not very long, as it is a more expensive method.
5. Series silencer method
This method is applicable to the attenuation of aerodynamic noise, which can effectively eliminate noise inside the fluid and suppress the noise level transmitted to the solid boundary layer. This method is most effective and economical for areas with high mass flow rate or high pressure drop ratio before and after the valve. The use of absorption type series silencers can significantly reduce noise. However, from an economic perspective, it is generally limited to attenuation to about 25 decibels.
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