The regulating valve is one of the widely used instruments of each device, and its accurate and normal operation has important significance for ensuring the normal operation and safe production of the process device. The reason of the vibration of the regulating valve will be described below.
The whole reason for the vibration of the regulating valve on the pipeline is as follows: The pipeline, valve core or base is violently vibrated, which can easily cause the entire regulating valve to vibrate. It is also related to the frequency, that is, when the external frequency is equal to or close to the natural frequency of the system. The vibrational energy reaches its maximum value and generates resonance.
These two factors sometimes affect each other and cause vibrations to become stronger and stronger, causing pipes to run out, loose attachments or components, and rattling noises. In severe cases, the valve stem breaks and the valve seat comes off, causing the system to fail to operate. This article mainly discusses the cause of valve body vibration.
1. Sometimes the velocity of the measured medium drastically increases, causing the differential pressure of the regulating valve to rapidly change. When the stiffness of the valve is exceeded, the stability of the valve deteriorates, which also causes severe oscillation of the entire regulating valve. However, this oscillation is not necessarily caused by the small opening of the valve. This vibration is generally accompanied by harsh squeaks.
2. The stability of the regulating valve is poor. Once the internal or external imbalance force interferes and exceeds the stiffness of the regulating valve, and the regulating valve itself does not have the ability to eliminate this interference, oscillation occurs. In this case, it is necessary to increase the stiffness of the regulating valve, such as the spring of 20 to 100 KPa, or to increase the stability of its operation, which has certain advantages. The valve should be installed away from the vibration source. If it is unavoidable, precautions should be taken.
This entire regulating valve vibrates, and in the case where resonance has not yet been reached, the regulating valve can basically be adjusted with an externally given signal. Because the relative displacement of the external reference signal to the spool is not changed or changed little by the vibration of the entire regulating valve, the reason is that they are a whole.
3. If the shutoff valve at both ends of the regulating valve is slammed or slammed, it will cause a strong reflection wave to be generated in the sharp flow measuring medium, and the reflected wave will impact the regulating valve core. When this force is greater than the diaphragm downward pressure on the spool, it will move the spool up, resulting in vibration, especially in the case of small signals, due to the smaller pre-tightening force, it is easier to make the spool vibrate.
4, the control valve opening is too small, so that the differential pressure before and after the valve is too large, so that at the throttle at the flow rate increases, the pressure rapidly reduced. If the pressure drops to the saturated vapor pressure of the liquid at this temperature, the liquid will vaporize, form flash, generate bubbles, and form a powerful pressure and shock wave when the bubble bursts, producing a gas hammer. This pressure is generally up to Dozens of MPa. The air hammer impacts the valve core, so that the valve core forms a honeycomb and makes the valve core vibrate.
5, regulator output signal instability. If the sensitivity of the valve positioner is too high, a small change or drift in the regulator output will immediately translate into a large output signal from the positioner. Causes the valve to oscillate.
6. The friction force of the regulating valve is too small. If the packing of the regulating valve is installed too little, or the gland is not tightened, the external input signal will have a slight change or drift and will be immediately transmitted to the valve core to make the valve core vibrate and issue. Giggles. On the contrary, if the friction force of the regulating valve is too large, if the packing is loaded too much, the gland is tightened too tightly, or the stuffing box is aged and dried up, it will not be able to move when the signal is small, and it will be generated when the signal is large. Excessive phenomenon will cause hysteresis oscillation of the regulating valve and the vibration curve will be a square wave. In this case, the damping of the corresponding part of the regulating valve should be reduced to solve, such as replacing the filler.
7. The fluctuation of the air source makes the output of the positioner fluctuate, or the active part of the positioner is rusted and inflexible, so that the input and output signals do not correspond and a skip-type oscillation occurs. At this point, open the gas source pressure reducing valve cleaning positioner and apply lubricant to the moving part to eliminate friction.
8. As a result of the imbalance force of the regulating valve itself, the regulating valve core often oscillates. The zero point spring tension is too small to resist external disturbances. In the case of small external signals, the valve core is easily vibrated.
Based on this situation, the pipes and pedestals that cause the vibration should be reinforced, which also helps to eliminate external frequency interference. Since the causes of oscillation are many, specific problems are analyzed. For vibrations with slight vibration, stiffness can be increased to eliminate it. Such as: choose a large spring stiffness, use the piston to implement the structure; pipeline, base violent vibration by increasing the support to eliminate vibration interference; the frequency of the election valve and the system frequency is the same, then replace the valve of different structures; work in the small opening caused by the oscillation , is the selection of improper circulation capacity C value selection, must be re-selection of the circulation capacity of the smaller C value or the use of split control or sub-valve to overcome the valve in the small opening.
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