Page 220 - Chemical engineering design

PIPING AND INSTRUMENTATION
The first letter indicates the property measured; for example, F D flow. Subsequent
letters indicate the function; for example, 197
I D indicating
RC D recorder controller
The suffixes E and A can be added to indicate emergency action and/or alarm functions.
The instrument connecting lines should be drawn in a manner to distinguish them from
the main process lines. Dotted or cross-hatched lines are normally used.

FRC

Figure 5.4. A typical control loop

5.3. VALVE SELECTION
The valves used for chemical process plant can be divided into two broad classes,
depending on their primary function:
1. Shut-off valves (block valves), whose purpose is to close off the flow.
2. Control valves, both manual and automatic, used to regulate flow.

(a) (b)
Figure 5.5. (a) Gate valve (slide valve) (b)Plugvalve