System Diagrams: An Update on Sources for Symbols

Well, its been a busy day of posting here at the ol’ Field Perspective on Engineering blog.  But I just was asked a good question by a couple of people with-in a fairly short  time span so I thought I would answer it with a post in case others have the same question.

Specifically, folks are wondering about where you get the symbols to use for system diagrams, something I discuss a bit in the post titled System Diagrams; an Industry Concept but Not an Industry Standard.  And apparently, one of the links in that post is broken.

So here are some answers and resources for those who are interested.  There are also some general thoughts and ideas about symbols derived from my experience that may be helpful to you.

One thing to realize is that there really is no universal standard for this sort of thing, at least not one that I know of;  that is one of the things that I talk about in the post I mentioned above.  That post has links to some of the symbol sets that are out there, but I think the one to ISA-5.1-1984 Instrumentation Symbols and Identification is now broken.  So, I have placed the copy I retrieved from the original link in my Google Drive account so you can link to it from there if you want to take a look at it. 

I should mention in doing this that I am never sure if posting a copy of a standard like that is “O.K.” or not.  My thinking is that spreading the word about stuff like that is a good thing for the industry and the organization that authored the guideline.  And my understanding from a number of people is that posting something like that for educational purposes, which is the point of this blog, is just fine.

But, its not out of the question that the reason the other link is broken is that somebody somewhere had an issue with providing the file.  So, I may end up being asked to “cease and desist”.  So, if at some point, you are reading this, and the link to my Google Drive does not work, that’s probably what happened.

·The ASHRAE Fundamentals Handbook has a chapter on symbols and abbreviations, and a lot of the stuff you see in your industry has its roots there. Many of the symbols are for floor plan type drawings but there are also symbols for schematics, etc. included.  I also have put a copy of the ASHRAE Fundamentals Handbook Symbols and Abbreviations Chapter on my Google Drive for your reference.

A lot of the symbols I use are ones I created in AutoCAD or in PowerPoint.  So, as you move forward with developing your system diagrams, you will develop a pretty good library of your own.  That can take a bit of discipline;  for one thing, you have to remember to save the symbol after you create it, which is a simple command in AutoCAD that writes it to its own little drawing file.  Otherwise, you will  find yourself opening a bunch of drawings looking for it the next time you need it.

And, I think most folks would agree that spending some time up front to organize the  symbols, both in terms of name and location can be worth it.  My symbol organization is not so good because I have hundreds of AutoCAD blocks that I created over the years.  But many of them started life as Generic CAD symbols (Generic CAD was an early CAD software package that was bought out by AutoDesk). 

Back in those days (and for a  while after that) file names were limited to 8 characters.  So folks like me had some fairly cryptic codes we used to name things.  Those codes probably only mean something to me.  And, since folks like me age and the neurons are firing quite as fast as they used to, there are some that I can’t quite remember so I find myself renaming things as I use them.

The symbols I used in my PowerPoint slides are just little Microsoft Drawing objects made up of lines and other shapes.  Once you make them, you can cut and paste them between slides or even between programs; i.e. something you created in PowerPoint can be pasted into Word or Excel.

The results are a bit more cartoonish than something you might create in CAD, at least when I do it, but still they are very usable.  So, I have uploaded a PowerPoint that has a couple of  my Microsoft Drawing object based system diagrams in them in case you want to use the symbols as a starting point.

There is a glossary that we hand out with the supplemental information in the RCx 101 class that I teach at the PEC.  It’s included in the appendix of the resource and reading list I have created and occasionally update and repost on the blog.  While it is not exactly a symbol list, it may be helpful in terms of understanding some of the common abbreviations and acronyms we use in the industry.

A lot of symbols are supplemented with text that kind of implies what they are, and probably what the symbols adjacent to them are.  For instance if you are looking at a system diagram at a symbol that is a circle with a triangle in it and there is  pump performance metrics next to it, like xxx gpm at yy ft.w.c., then that is probably the symbol that is being used for a pump, and the symbols in the pipe on either side of it are probably for things commonly found next to a pump, like the service valves, discharge throttling valve, flex connectors, and strainers.  So often, you can imply what the symbols are from their context combined with the tendency to make symbols look a little like what they represent, if not physically then functionally.

What really matters, bottom line, is that the symbols mean something to you if you develop them, which is where the folks asking questions are hopefully headed in terms of thinking about symbols for their system diagrams.  And the flip side of the coin is that if you use symbols, it would be good to define them somehow with a symbol list that is included with the drawing set you put out.  That is the challenge that some of you are probably dealing with;  i.e. looking at drawings without the benefit of the symbols list associated with them.

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