How to prevent and reduce control valve noise

1. Eliminate resonance noise.

Only the regulator resonates when there is a strong noise energy superimposed and produces more than 100 decibels. Some show strong vibration and low noise, and some weak vibration, very loud noise and large vibration and noise. This noise produces a tonal sound with a frequency of 3000 7000 Hz.

Obviously, the resonance is eliminated and the noise disappears naturally.

2. A way to eliminate cavitation noise.

Cavitation is the main hydrodynamic noise**. When the cavitation bubble bursts at high speed, it produces strong turbulence and cavitation noise in the local area. This noise has a wide range of frequencies, chattering, similar to the sound of a fluid containing sand.

Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.

3. The use of thick-walled pipes.

Use one of the acoustic treatments on thick-walled pipes. The use of thin walls can create an increase in noise by 5 dB, and thick-walled pipes can reduce noise by 0 20 dB. With the same wall thickness and the same diameter of the pipe with the same wall thickness, the greater the noise, the better the effect.

DN200 pipes, whose wall thickness is, 8th, 10th, 15th, 18th, 20th, mm, can reduce noise, respectively, 2 - increase daily decibels. Of course, wall thickness comes at a higher price.

4. Use sound-absorbing materials.

This is also a more common and most effective method. Sound barriers can be made with sound-absorbing materials, covers, noise sources, and behind-valve piping. It must be noted that because noise is transmitted through fluid flow and over long distances, the effectiveness of noise reduction in the sound-absorbing material package, using thick-walled tubes, is terminated at **.

This method is suitable for low noise and not long pipes, as it is more expensive way.

5. The method of series mufflers.

This method is applicable to aerodynamic noise, which can effectively eliminate noise and suppress the noise level transferred to the solid boundary inside the fluid. High quality flow rates or valve front and rear pressure drop ratios are the most efficient and economical. Noise can be greatly reduced by using absorption-type series mufflers.

From economic considerations, however, it is generally limited to decay of about 25 decibels.

6. The method of soundproof box.

Use soundproof frames, houses and buildings, isolate noise, reduce noise from the external environment, and people can accept the range.

The selection, calculation and design of the control valve are very important, and it is recommended to consult a professional control valve manufacturer to ensure the quality of the control valve.

Low-noise control valves are commonly used with throttle control valves and butterfly valves. In the process of use, if there is a problem with the valve, it needs to be repaired and maintained accordingly. Common problems include clogged valve nozzles, leaking valves, inaccurate valve openings, and worn valve stems and discs.

When you encounter these problems, you can take different measures to maintain them. For the blockage of the valve nozzle, the method of cleaning the pipe can be taken to solve it. If there is a leak in the valve, it is necessary to check whether the valve seal is intact and whether the seal needs to be replaced.

If the valve opening is not accurate, you can check the valve transmission mechanism, and refuel and moisten the potato bush in time. In addition, it is important to regularly inspect and maintain the low-noise control valve to effectively extend the service life of the valve. Valves can be thoroughly inspected once a year, including cleaning pipes, inspecting seals, cleaning valves and transmission mechanisms, and more.

When the control valve is used, it will sometimes produce a certain amount of noise, and the method of eliminating the noise is:

1) Resonance noise elimination method.

Only when the regulating valve resonates, can the energy superimpose and produce a strong noise of more than 100 decibels. Some are characterized by strong vibration and not much noise, and some are weak and very loud; Some of them are loud in vibration and noise. This noise produces a monotonal sound with a frequency of 3000 7000 Hz.

Obviously, the resonance is eliminated and the noise naturally disappears. Cavitation noise elimination.

Cavitation is a major source of hydrodynamic noise. During cavitation, the bubble bursts to produce a high-velocity impact, causing strong local turbulence and cavitation noise. This noise has a wide frequency range and produces a latchic sound, similar to the sound produced by a fluid containing sand and gravel.

Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.

3) Use the thick-walled pipeline method.

The use of thick-walled tubes is one of the sound path treatment methods. The use of thin walls can increase the noise by 5 decibels, and the use of thick-walled pipes can reduce the noise by 0 to 20 decibels. The thicker the wall of the same pipe diameter, the larger the pipe diameter of the same wall thickness, the better the noise reduction effect.

4) Adopt the sound-absorbing material method.

It is also one of the more common and most effective vocal path treatments. Noise sources and behind-valve pipelines can be covered with sound-absorbing materials. It must be pointed out that because the noise will be transmitted over a long distance through the flow of fluids, the sound-absorbing material is wrapped to the first level, and the thick-walled pipe is used to the first level, and the effectiveness of noise elimination is terminated.

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.

The causes of pressure reducing valve noise can be divided into the following three categories:

1. The parts and components of the noise pressure reducing valve generated by mechanical vibration will produce mechanical vibration when the fluid flows, and the mechanical vibration can be divided into two forms: 1) low-frequency vibration, which is caused by the jet and pulsation of the medium, and the reason for this is that the flow rate at the outlet of the valve is too fast, the pipeline layout is unreasonable and the rigidity of the valve moving parts is insufficient.

2) High-frequency vibration, this vibration will cause resonance when the natural frequency of the valve is consistent with the excitation frequency caused by the flow of medium, which is generated by the pressure reducing valve within a certain range of pressure reduction, and once the conditions change slightly, its noise changes greatly. This kind of mechanical vibration noise has nothing to do with the flow speed of the medium, and is mostly caused by the unreasonable design of the steam pressure reducing valve itself. Measures to reduce mechanical vibration and noise are to reasonably design the gap between the bushing and stem of the pressure reducing valve, the machining accuracy, the natural frequency of the valve, the rigidity of the moving parts, and the correct selection of materials.

2. Hydrodynamic Noise Hydrodynamic noise is generated by the turbulence and vortex after the fluid passes through the pressure reducing port of the pressure reducing valve, and the process can be divided into two stages:

1) Turbulent noise, that is, the noise generated by the interaction between the turbulent fluid and the inner surface of the pressure reducing valve or pipeline, its frequency and noise level are relatively low, and generally do not constitute a noise problem.

2) Cavitation noise, that is, in the process of pressure reducing valve, when the fluid flow rate reaches a certain value, the fluid (liquid) begins to vaporize, and when the pressure of the bubbles in the liquid reaches a certain value, it will be **. When the bubble is in the center, it will produce a high pressure and shock wave locally, and the pressure of this impact can reach 196MPa, but far away from the center of the country, the pressure will decay sharply. This shock wave is a major contributor to cavitation and noise in pressure reducing valves.

The measure to reduce mechanical vibration and noise is that when designing the pressure reducing valve, the pressure reducing value of the pressure reducing valve must be controlled below the critical value, and it is best to be below the initial value of δp, because when the actual pressure reducing value of the pressure reducing valve reaches the initial value of δp, the liquid begins to cavitate, and the noise will increase sharply. In addition, attention should be paid to the direction of flow of the fluid medium relative to the disc.

3. Aerodynamic noiseWhen compressible fluids such as steam pass through the pressure reducing part in the pressure reducing valve, the noise generated by the conversion of the mechanical energy of the fluid into sound energy is called aerodynamic noise. This noise is one of the most common noises in pressure reducing valves and the most troublesome to deal with. The causes of this noise are divided into two situations, one is due to the turbulence of the fluid, and the other is due to the shock wave caused by the fluid reaching a critical flow velocity.

Aerodynamic noise cannot be completely eliminated because it is inevitable that the pressure reducing valve will cause fluid turbulence when reducing pressure.

The noise of the control valve is mainly caused by eddy currents, and the way to reduce the noise is to minimize the eddy currents! For example, try to be as smooth as possible, the opening should be as large as possible (preferably fully open), and the size of each control valve in the control valve group should be staggered.

In the on-site use of control valves, many of them are often not caused by the quality of the control valve itself, but by the improper installation and use of the control valve, such as improper installation environment, installation position and direction, or unclean pipelines. Therefore, the following aspects should be paid attention to when installing and using the electric control valve:

1) The control valve is a field instrument, which requires that the ambient temperature should be in the range of 25 to 60 and the relative humidity is 95%. If it is installed in the open air or in a high-temperature place, waterproof and cooling measures should be taken. In places where there is an earthquake source, it is necessary to stay away from the vibration source or increase anti-vibration measures.

2) The control valve should generally be installed vertically, and it can be tilted under special circumstances, such as when the tilt angle is large or the weight of the valve itself is too large, the valve should be protected by supporting parts.

3) The pipeline of the installation of the control valve should generally not be too high from the ground or floor, and the platform should be set up as much as possible when the pipeline height is greater than 2m, so as to facilitate the operation of the handwheel and facilitate the maintenance ......

Will it be?!

Nonsense! Noise is caused by a flow rate that is too fast, or worse, by flashing or cavitation – and the spool is ruined ......

This shows that the selection is wrong!

If it is prevented, it should be carefully calculated when selecting (pay attention to the flow rate), and consider the flash and cavitation to prevent it (cage or even labyrinth in the form of spool, or multi-stage pressure reduction).

Among the environmental protection issues of the use of control valves, the noise problem is very prominent.

Due to the use of the control valve, it will inevitably cause the decompression, speed change and vibration of the fluid, and the noise generation is unavoidable, and the problem is to control the size of the noise.

In process devices, the equipment that can generate noise includes electric motors, pumps, compressors, boilers, control valves, etc., and the noise of control valves accounts for a large proportion.

The types of control valve noise are mechanical, hydrodynamic and aerodynamic. In view of its generation mechanism, it should be estimated and preventive measures should be proposed when selecting the control valve.

The selection is correct, and the flow rate is not too small.