Microsoft Word Course Control valves R. doc

General Good Engineering Guidelines

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Control Valves Basics - Sizing & Selection
FMD3x00 98 DB Initialize (5), configuration-and-evaluation-software-pi-9045582-en-gb, configuration-and-evaluation-software-pi-9045582-en-gb, Document, colour present

General Good Engineering Guidelines
1. The control valve size is generally smaller than the corresponding line size. This change in diameter should be clearly indicated in the P&ID with a reducer and expander.
2. Provide manual block and bypass valves around control valves where practical to allow for control valve removal and servicing while the system is operational. If a manual bypass is not provided then furnish the valve with a hand wheel.
3. A drain valve is normally always provided between the control valve and upstream isolating valve. If the control valve is of Fail Open type, this drain valve is sufficient to drain the piping segment. If the control valve is of Fail Close or Fail in Position type, then additional drain valve is required between the control valve and downstream isolating valve.
4. Additional details such as failure position, tightness class, # rating etc. are also indicated on the P&ID for control valves, as per the project standards.
5. End Connections

• Threaded ends are cheap but can be stripped and leak use these where this isn’t a worry.
• Welded ends provide no leaks and are cheap initially, but if there are problems the valve must be cutout Flanged ends are the most expensive but are the best from an installation and removal standpoint.
6. Locate control valves at grade where practical. Install the control valve near the operating equipment that has to be observed while in local manual control.
Equipment must be located so that they do not interfere with each other and so that space is available for people to travel through the process and perform tasks, such as maintenance.

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