Instrumentation flow sheet symbols

Useful equipment symbols are shown in Fig. 3-7. Other types of symbols are illustrated in Fig. 3-2. Drawing templates for some of these symbols are available. As mentioned previously, flow-sheet symbols are not as yet standardized within the industry. Hence, symbols should Compass Instrument and Optical Co., New York. 

Instrummiaiion flow sheets are useful in determining the requirements for process control and instrumentation. The Instrument Society of America has pioneering standardization of instrumentation flow plan symbols. These systems of nomenclature are illustrated in Tables 3-1... 

Data on spare and parallel equipment are often omitted. Valving is also generally omitted. A alve is shown only where its specification can aid in understanding intermittent or alternate flows. Instrumentation is indicated to show the location of variables being controlled and the location of the actuating device, usually a control valve. To help the reader better understand the process flow sheet, a list of commonly used symbols is presented in Fig. 5.9.1. 

Drawings should conform to accepted drawing conventions, preferably those laid down by the national standards. The symbols used for flow-sheets and piping and instrument diagrams are discussed in Chapter 4. Drawings and sketches are normally made on detail paper (semi-transparent) in pencil, so modifications can be easily made, and prints taken. 

The symbols used to show the equipment, valves, instruments and control loops will depend on the practice of the particular design office. The equipment symbols are usually more detailed than those used for the process flow-sheet. A typical example of a P and I diagram is shown in Figure 5.25. 

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