I'm aware that answers may vary and it really does depend on the company/country where the PID was drawn but I have checked back for the last 30 years and found no drawing legend that describes what this symbol is and was hoping someone could point me in the correct direction.

enter image description here

The symbol being "GOS±"

  • $\begingroup$ What do the HS and LISA components refer to? $\endgroup$
    – jko
    Jan 28, 2020 at 15:04
  • $\begingroup$ If the lead sheet for the set this drawing belongs to doesn't say what GOS and (+/-) stand for, you're really in trouble. Someone might be able to guess if you gave a detailed description of what this P&ID is meant to represent in the physical world. I personally have no clue what "G" as the first letter would mean. $\endgroup$
    – J. Ari
    Jan 28, 2020 at 17:43
  • $\begingroup$ Considering that PID labels tend to mean things in English I suspect this is a foreign language. Temperature of concentration control maybe? $\endgroup$
    – Tiger Guy
    Jan 28, 2020 at 17:57
  • 1
    $\begingroup$ @jko HS - Hand Switch, LISA = Level Indicator Sensor Alarm $\endgroup$
    – SimpleJack
    Jan 29, 2020 at 9:31
  • 1
    $\begingroup$ Given that the question is tagged with control engineering, it might help to write "P&ID" instead of "PID" in the question, to avoid confusion with the very common PID closed-loop controller. $\endgroup$ Jan 30, 2020 at 14:20

3 Answers 3


This is an instrument symbol, they are read in the following way,

ISA Symbology

The symbology of the instrument it is placed in a circle of 7/16 “or 12 mm (see below), was in the top there is the functional identification (of the instrument or device) composed with max 5 letters, and in the bottom there is identification of the loop (measurement and/or control) consists of a progressive number of 3 or 4 numbers, followed by a literal suffix to identifies two or more identical instruments inserted in the same chain and therefore having the same functional identification

  1. First letter, (what is being measured)
    1. Following Letters, which can be passive, active, and a modifier
    2. The Bottom numbers are which loop they run on.

So in your case:

  • G - Is specifically User choice, which in this case may mean Gas.
  • O - Orifice or a restriction
  • S - Switch

Morbo explains the logic quite well, however I disagree regardin the meaning of the letters. According to the IEC 62424 (which would specify H/L instead of + -)

G means distance or position is measured
O is local display or display on SCADA
S means switch +- wiould refer to the two positions something switches on

Since all the GOS+- operate on valves I'd say that these are the limit switches, to display valve position on the SCADA and supply position data for control purposes.


According to my experience the symbol GOS stands for the valve stem position switch (limit switch), GOS+ = valve open (stem in high position), GOS- = valve closed (stem in lowposition). In old P&ID's letter G denoted position.

  • $\begingroup$ How old is old...90s or 80s? $\endgroup$ Mar 27, 2021 at 17:58

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