In this blog, I will discuss about the control valve assembly and its location in the process plant. The control valve assembly is also called as control valve station.
Table of Contents
What Is Control Valve Assembly
Control Valve assembly is a vital components in process plants, strategically placed during plant design. Their main purpose is to ensure uninterrupted system operation during Control Valve maintenance.
To achieve this, Control Valve assemblies typically incorporate two isolation valves and a bypass line. During normal operation, the bypass line remains inactive.
However, during maintenance, the bypass line comes into play. By closing the gate valve on the main line and activating the bypass, the Control Valve can be easily repaired without disrupting the entire system.
This setup ensures the continuous functionality of the process while essential maintenance is carried out.
Control Valve Assembly Location:
Control valve assembly should be located at ground FFL, FGL) Or operating platform. always try to locate this assembly in vertical direction to avoid extra space considering some exceptions.
Important Points For Control Valve
- Control Valve comes under the scope of the Instrumentation Department.
- Information about the control valve can be found in Hook Up Drawing.
- Sizing of the control valve is done by an Instrument Engineer.
- Control valve size is one or two sizes smaller than line size in most cases.
- Rating: Higher than the line rating.
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Design Consideration For Control Valve Station
- The control valve should be flange end for ease of removal during maintenance.
- The control valve and it’s connecting flange, gasket, and fasteners should be of a higher rating than the line rating.
- The size of the control valve will be one or two sizes smaller than the line size.
- Reducers are required at both sides of the control valve to joint different diameters of the pipe, because of the different sizes of the line and control valve.
- Concentric reducers can be used to maintain the flow pattern, but for ease of support eccentric reducer flat side down is preferred.
- Drains are required at both sides of the control valve to equalize pressure between the isolation valve and the control valve.
- The upstream drain is used, if the control valve fails to open and both the drains are used, if the control valve fails to close.
- Drains can be welded directly on the reducer if the reducer size is more than 8″.
- Isolation valves are required at both sides of the control valve for isolating the line during the maintenance work.
- The size and rating of the isolation valve should be the same as the piping flange rating and the size.
- The bypass is required to keep the system in running condition during control valve maintenance.
- Bypass size should be the minimum same as the control valve’s size.
- Globe valve should be preferred as a bypass valve as it is the best regulation valve.
- The bypass valve should be located upstream side to avoid fluid hammer on the bypass valve disc.
- A pressure Gauge is required in the control system to measure and control the pressure during maintenance.
- The pressure Gauge should be located downstream side of the control valve after the bypass.
- Control Station is kept at the operating level for ease of maintenance, which should be a minimum of 500 mm to 600 mm above the operating level.
- Supports are required at both sides of the control valve to take care of the weight.
- support should be a minimum of 300 mm away from the flange joint for removal of the bolt.
- Support can be allocated either below the reducer or elbow.
- To take care of the thermal expansion and to make the system stress-free both supports should be resting support.
- In case of vibration downstream side support should be anchor support and the upstream side should be resting support.
- Axial and guide support can be used for controlling the pipe movement.