DOE-HDBK-1016/1-93ENGINEERING FLUIDS DIAGRAMS AND PRINTSEngineering Fluid Diagrams and PrintsFigure 5 Control Valves with Valve PositionersIn Example A of Figure 5, the reader can reasonably assume that opening of the control valveis in some way proportional to the level it controls and that the solenoid valve provides anoverride of the automatic control signals. However, the reader cannot ascertain whether it opensor closes the control valve. Also, the reader cannot determine in which direction the valve movesin response to a change in the control parameter. In Example B of Figure 5, the reader can makethe same general assumptions as in Example A, except the control signal is unknown. Withoutadditional information, the reader can only assume the air supply provides both the control signaland motive force for positioning the control valve. Even when valves are equipped withpositioners, the positioner symbol may appear only on detailed system diagrams. Larger, overallsystem diagrams usually do not show this much detail and may only show the examples ofFigure 5 as air-operated valves with no special features.ControlValveDesignationsFigure 6 Control Valve DesignationsA control valve may serve any number of functions within a fluid system. To differentiatebetween valve uses, a balloon labeling system is used to identify the function of a control valve,as shown in Figure 6. The common conventionis that the first letter used in the valve designatorindicates the parameter to be controlled by thevalve. For example:F = flowT = temperatureL = levelP = pressureH = hand (manually operated valve)The second letter is usually a "C" and identifiesthe valve as a controller, or active component, asopposed to a hand-operated valve. The thirdletter is a "V" to indicate that the piece ofequipment is a valve.PR-02Rev. 0Page 6
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