Engineering Fluid Diagrams and PrintsDOE-HDBK-1016/1-93FLUID POWER P&IDsValvesValves are the most complicated symbols in fluid power systems. Valves provide the control thatis required to ensure that the motive media is routed to the correct point when needed. Fluidpower system diagrams require much more complex valve symbology than standard P&IDs dueto the complicated valving used in fluid power systems. In a typical P&ID, a valve opens, closes,or throttles the process fluid, but is rarely required to route the process fluid in any complexmanner (three- and four-way valves being the common exceptions). In fluid power systems itis common for a valve to have three to eight pipes attached to the valve body, with the valvebeing capable of routing the fluid, or several separate fluids, in any number of combinations ofinput and output flowpaths. The symbols used to represent fluid power valves must contain much more information than thestandard P&ID valve symbology. To meet this need, the valve symbology shown in thefollowing figures was developed for fluid power P&IDs. Figure 24, a cutaway view, providesan example of the internal complexity of a simple fluid power type valve. Figure 24 illustratesa four-way/three-position valve and how it operates to vary the flow of the fluid. Note that inFigure 24 the operator of the valve is not identified, but like a standard process fluid valve thevalve could be operated by a diaphragm, motor, hydraulic, solenoid, or manual operator. Fluidpower valves, when electrically operated by a solenoid, are drawn in the de-energized position.Energizing the solenoid will cause the valve to shift to the other port. If the valve is operatedby other than a solenoid or is a multiport valve, the information necessary to determine how thevalve operates will be provided on each drawing or on its accompanying legend print. Figure 24 Valve OperationRev. 0PR-02Page 27
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