Regarding the selection of control valves
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Colleagues, due to inadequate preliminary work in the selection of control valves, the pressure difference before and after the valve was set too low, while the actual pressure difference at those locations is quite high. The flow capacity and diameter of the control valves currently in use are too large, which prevents automatic control. I would like to ask my colleagues for solutions other than reselecting and replacing the control valve.
Close the shut-off valve in front of the control valve, or install a flow restrictor in front of the control valve
Depending on the situation, it is possible to recalculate and replace the components inside the valve, which can save some money.
I have painful lessons to learn in this regard. This is due to the inaccurate pressure difference before and after the valve as provided by the process (the parameters for the pressure difference before and after the valve are too low; in actual operation, this pressure difference is much higher than the design value, resulting in severe vibration of the valve body during automatic control and damage to the valve core). The suggestions provided for the 2nd floor are theoretically feasible, but they are difficult to implement in actual process operation, as they result in a reduction in fluid flow rate, failing to meet the process requirements; moreover, this is not conducive to the normal operation of the process over the long term. The approach we finally adopted was to recalculate and replace the valve internals (mainly the valve spool), and it has been working well ever since.
Friend on the fourth floor, the problem is that the manufacturer refuses to carry out the replacement. We’ve considered installing flow-limiting orifice plates as well, but in an emergency, insufficient flow can lead to safety accidents. I’m talking about the drainage control valve of the distillation tower here. Is there a better way?
From a process perspective, if it is not possible to install a flow-limiting device, auxiliary control can be achieved by using the dual lines of the control valve, or an additional pipeline can be added from the bottom drainage line to feed directly into the next process; however, the diameter of this pipeline should not be too large – a 20 mm diameter pipeline could be considered.
Close the manual valve in front and reduce the P value to allow greater variation in the automatic control valve
Effectively utilizing the opening degrees of the front and rear shut-off valves for proportioning is the most economical and efficient approach
This post was last edited by heicafei on 2012-7-11 00:00. Shouldn’t a flow-limiting orifice plate be installed after the control valve in order to increase the pressure drop behind the valve, thereby reducing the pressure difference across the control valve? If the flow-limiting orifice plate is placed before the control valve, wouldn’t that result in an even larger pressure difference across the control valve?
Basically, replacing the valve core is the solution; how can the manufacturer prevent this from being done? You can simply purchase a set and replace it yourself. Installing a flow control device requires approval from the engineering team, as such devices will definitely affect the operating conditions of the medium, so it’s best to avoid doing this. Throttling elements must not be added arbitrarily