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Thread: Correct Symbols for Use in Piping and Instrumentation Diagrams

  1. #1
    Associate Engineer
    Join Date
    Oct 2017

    Correct Symbols for Use in Piping and Instrumentation Diagrams

    I am working on P&IDs for process control systems and I am finding conflicting information and inconsistent symbols in various locations. Does anyone have a recommendation for a good and complete library of symbols. Is this a truly standardized practice? or are there variations that are acceptable?

    Here are some examples:

    I consider this to represent a generic valve.
    I have seen it labeled specifically as a gate valve (in a library - not a drawing)

    I have seen both of the first 2 labeled as Ball valves... the 2nd labeled as a diaphragm valve... the same with only the top arc of the circle as a diaphragm also... then, in the same library, the third is a 3-way plug valve. It makes more sense to me that the third is a 3-way ball valve. especially when I have seen a 2-way plug valve represented as:

    and aren't all of the symbols that I have used incomplete anyway? none of them include actuation. Does that mean it is assumed to be manual? because there are also versions that I see with a "T" shaped line coming out the top of the center of all of these... which is for manual.

    I guess the heart of my question is "Am I being to anal about this?" since all of the components will be further specified with text and part numbers is it OK to have slightly varied symbols? is any of this a matter of personal preference? or shall we say "dialect"?

    At this point, I plan on developing a complete library for myself to use. With the generic 2-triangle valve symbol as the base, center shapes like a hollow circle for ball, filled circle for globe, diamond for plug, vertical line for gate, filled downward triangle for needle, angled line for butterfly, etc.

    Does anyone know if there is an "official standard" for these? if so, where can I find it.
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  2. #2
    christaras90's Avatar
    Join Date
    Oct 2017
    Thessaloniki, Greece
    I also work with P&IDs. Based on one of our company's practices (for symbology), we developed an Index-P&ID for this reason. In practice, we use only the 2-triangle symbol with the circle in the middle for ball valves and the simple 2-triangle symbol for the rest of the valves (except control valves of course).

    I recommend that you use ANSI/ISA-5.1-2009.

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