Vibration of instrument valves
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I work in gasification, not in the field of instrumentation. I just wanted to ask those who are experienced in instrumentation: when the pressure difference before and after a self-regulating valve is large, the valve starts to oscillate. Does this oscillation refer to the valve moving back and forth, or is it some other phenomenon? Looking forward to answers……
When the pressure difference is large, this high difference causes the control valve to open more, resulting in a consistently high flow rate!
It is mainly the vibration of the valve itself; the valve stem also experiences vibration, which ultimately leads to unstable regulation!
In the case of a liquid fluid, an excessive pressure difference before and after the valve can cause flashing or cavitation behind the valve, leading to valve oscillation. When the valve is operated at a low opening degree, the pressure difference before and after it increases, the control accuracy declines, and oscillations may also occur. If it is a gaseous fluid, an excessive pressure difference before and after the valve can cause supersonic flow to occur behind the valve, resulting in noise and oscillations. The solution is that if the valve operates at a low opening degree for an extended period, it indicates that the valve size is too large; after recalculation, a control valve with an appropriate size should be installed. A sleeve-type control valve can be selected. Under the premise of process permission, a porous flow restrictor is installed downstream of the valve for gaseous fluids to increase the pressure downstream of the valve