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PID Drawing

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Flow Diagrams and InstrumentationFlow Diagrams and InstrumentationFlow Diagrams and InstrumentationFlow Diagrams and Instrumentation 113113113113

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The flow diagram is a dynamic document. It may be revisedand updated during the project to reflect the client’s changes ormodifications imposed by governmental regulations.

Figure 7-3 shows a sample utility flow diagram.

FLOW DIAGRAM INSTRUMENTS

Instruments function by sensing changes in the vari-ables they monitor. The four basic instrument groups are:

Flow (F)Level (L)Pressure (P)Temperature (T)

The types of instruments used to sense, control andmonitor these variables are:

Controller (C)Indicator (I)Gauge (G)Alarm (A)Recorder (R)

By learning these nine terms, students will be able tounderstand most of the instrument symbols found on amechanical flow diagram.

Figure 7-4 illustrates a combination of the symbols andabbreviations used to represent an instrument’s functionon flow diagrams. The first letter in the symbol indicatesthe instrument group, and the second and/or third lettersindicate the instrument type.

To indicate a change or to control the flow, level, pres-sure, or temperature, an instrument must first sense achange in the variable. Once a change has been detected,the instrument then transmits this information viamechanical, electronic, or pneumatic means to a controlpanel where it can be observed and recorded. At the sametime, the instrument may activate other devices to affectand change process conditions in the facility. Someinstruments are read in the plant at the instrument’s actuallocation. Others are displayed on a control panel locatedin an operator’s control room.

Instrument Types

Gauges. Gauges are instruments that measure the liq-uid level inside a vessel or the temperature and/or pres-sure in the piping system. Level, temperature, or pressuregauges are locally mounted to enable plant operators toobtain a visual reading.

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II

Equipment Layout

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Equipment Location Drawing

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Piping Arrangement Drawings, Sections, and ElevationsPiping Arrangement Drawings, Sections, and ElevationsPiping Arrangement Drawings, Sections, and ElevationsPiping Arrangement Drawings, Sections, and Elevations 157157157157

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III

Nozzle Orientation

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IV

Pipe Rack

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Section & Piping Layout

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