READING ENGINEERING P&IDs DOE-HDBK-1016/1-93 Engineering Fluid Diagrams and Prints READING ENGINEERING P&IDs Standards  and  conventions  have  been  developed  to  provide  consistency  from drawing  to  drawing.    To  accurately  interpret  a  drawing,  these  standards  and conventions must be understood. EO  1.9 STATE how the following  valve conditions are depicted  on an engineering  P&ID   drawing: a. Open  valve b. Closed  valve c. Throttled  valve d. Combination  valves (3-  or  4-  way  valve) e. Locked-closed  valve f. Locked-open  valve g. Fail-open  valves h. Fail-closed  valve i. Fail-as-is valve Standards  and  Conventions  for  Valve  Status Before  a  diagram  or  print  can  be Figure 17   Valve Status Symbols properly read and understood, the basic conventions  used by P&IDs to    denote   valve    positions   and failure modes must be understood. The    reader    must    be    able    to determine the valve position, know if  this  position  is  normal,  know how  the  valve  will  fail,  and  in some  cases  know  if  the  valve  is normally  locked  in  that  position. Figure  17  illustrates  the  symbols used    to    indicate    valve    status. Unless   otherwise   stated,   P&IDs indicate  valves  in  their  "normal" position. This is usually interpreted    as    the    normal    or primary  flowpath  for  the  system. An  exception  is   safety  systems, which are normally shown in their standby or non-accident condition. 3-way valves are sometimes drawn in the position that they will fail to instead of always being drawn in their "normal" position.   This will either be defined as the standard by the system of drawings or noted in some manner on the individual drawings. PR-02 Rev. 0 Page 16