ISO 3511-4:1985

The symbols in this part shall be considered a supplement to the symbols given in ISO 3511/1 and ISO 3511/2 and used in conjunction with them. The letter code for function identification shall be taken from table 1 of these two parts.The symbols are limited to identification on process flow diagrams, piping and instrument diagrams, etc. and do not provide means of illustrating specific instruments or parts thereof. The application methods are shown in the examples.