In production, we sometimes find that regulators, pressure relief valves and other throttles generate severe vibration and noise. In fact, the vibration and noise generated at the same time, the valve spool, valve seat and other internal parts were severely washed, resulting in a road wear marks, deep grooves and pits, and some even cause the valve stem fracture, which have a serious impact Valve performance, reducing the service life.
Control valve vibration and noise according to its different evoked factors can be divided into mechanical vibration, cavitation vibration and fluid (vortex) vibration and other reasons.
Causes vibration and noise
Cavitation vibration
Cavitation vibration generally occurs in the liquid medium control valve. The fundamental cause of cavitation is that the liquid in the regulating valve is accelerated by the systolic flow and the static pressure is decreased. The smaller the opening of the control valve is, the larger the pressure difference between the front and the back is. The more the fluid accelerates and cavitation is generated, and the corresponding pressure drop of the blocking flow is smaller.
Mechanical vibration
Mechanical vibration according to its manifestations can be divided into two states. One state is the overall vibration of the regulating valve, ie the entire regulating valve vibrates frequently on the pipe or base, due to violent vibrations of the pipe or base causing the entire regulating valve to vibrate. In addition, 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 energy of the forced vibration reaches a maximum value and resonance occurs. Another state is the valve flap vibration, the reason is mainly due to the rapid increase of the medium flow rate, the rapid change before and after the control valve pressure, causing the entire control valve to produce severe oscillations.
Vortex vibration
The fluid is throttled in the valve and due to friction, drag and various disturbances, it inevitably produces a wide range of eddy currents, such as fluid striking a valve stem, passing through gaps, cornering when turning, At the time of diversion, whirlpool flows are generated, and the whirlpool flows interact with the cylinder to induce vibration and generate vortex detached sound. Once the excitation frequency of the gas flow is coupled with the natural frequency of the mechanical element or with the longitudinal gas column standing wave in the pipe, lateral air column oscillation, thermal shock, gas-dynamic compression or other unsteady flow When the vibration increases, the noise increases. If the fluid flows through the control valve to produce flash, a gas-liquid two-phase mixture exists, and the deceleration and expansion of the two-phase fluid will also form noise. In addition, cavitation, the bubble rupture release powerful energy, will produce up to 10000Hz noise, the more the bubble, the more serious the noise.
How to deal with vibration and noise
For cavitation
First of all, should avoid the work of small openings. The opening of the control valve is too small, resulting in increased velocity at the orifice, the pressure decreases rapidly, the fluid flow through the valve is easy to form flash and cavitation. Yijun Jun in this article, "click here" mentioned the small valve opening caused by cavitation damage, we must not ignore.
Second, multi-level distribution pressure drop should be used. To prevent cavitation the most effective way is to make the pressure drop at all levels within the valve are less than the minimum pressure difference occurs cavitation, the critical pressure. When the control valve to withstand the pressure is far greater than the critical pressure, multi-stage structure can be used to reduce pressure. In the design of multi-stage throttling control valve, so that each level of throttle to withstand the pressure difference is less than the allowable pressure, so that each level of energy consumption, making the next level of population pressure is relatively low, reducing The next level of pressure, low pressure recovery, this can reduce the throttl