Going through one P&ID of gas processing facility I have been working. What are the reasons behind placing RO-restricted orifice after control valve/valve? To my knowledge RO use in measuring flow rate and creating pressure drop. But I need more reasons for this case putting after valve with explanation/calculation.RO means restriction orifice.  Therefore it restricts flow. An orice used for flow measurement requires pressure measurement either side.
Where is the RO?  Is it on a vent line or a liquid drain line? Is it a control valve or an actuated valve. What is the valve controlling?
If on a liquid drain line it will be to limit gas break thorough if the  valve fails open so to prevent gas over pressuing of receiving vessel / pipework.
If on a vent - it is to control the venting. The RO (restriction orifice) purpose is to limit the flow:
- for example in flare system lines to provide sufficient purge gas capacity, not to allow any increasment of it. PCV are always sized for higher rates than application requires and RO is the way how to keep your purge rate at min.
- sometimes RO are used at drain lines from compresors' scrubbers. If gas somehow escapes through this line, there will be a sound that may warn operators about the upsets

MORE NEWS