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PRIORITY VALVES
MAINTENANCE - 14104_148

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Figure  9-31.—Valve  manifold  showing  cutaway  view  of  the valves and typical combination of suction and discharge valves. When the pressure in the valve reaches 1500 psi, the  poppet  reaches  the  end  of  its  travel.  As  the pressure increases, the piston continues to move to the right, which unseats the poppet and allows flow  through  the  valve,  as  shown  in  view  A  of figure 9-30. If the pressure drops below 1500 psi, the  compressed  spring  forces  the  piston  to  the  left, the  poppet  seats,  and  flow  through  the  valve stops. Figure 9-30, view B, shows the priority valve in the free-flow position. The flow of fluid moves the   poppet   to   the    left,  the  poppet  spring compresses, and the poppet unseats. This allows free  flow  of  fluid  through  the  valve. VALVE   MANIFOLDS Sometimes suction must be taken from one of many sources and discharged to another unit or units of either the same or another group. A valve manifold  is  used  for  this  type  of  operation.  An example of such a manifold (fig. 9-31) is the fuel oil  filling  and  transfer  system  where  provision must be made for the transfer of oil from any tank to  any  other  tank,  to  the  service  system,  or  to another  ship.  If,  for  example,  the  purpose  is  to transfer  oil  from  tank  No.  1  to  tank  No.  4,  the discharge  valve  for  tank  No.  4  and  the  suction valve from tank No. 1 are opened, and all other valves are closed. Fuel oil can now flow from tank No.   1,   through   the   suction   line,   through   the pump, through the discharge valve, and into tank No.  4.  The  manifold  suction  valves  are  often  of the stop-check type to prevent draining of pumps when  they  are  stopped. VALVE   HANDWHEEL   IDENTIFICA- TION  AND  COLOR  CODING Valves  are  identified  by  markings  inscribed  on the  rims  of  the  handwheels,  by  a  circular  label plate secured by the handwheel nut, or by label plates  attached  to  the  ship’s  structure  or  to  the adjacent  piping. Piping  system  valve  handwheels  and  operating levers  are  marked  for  training  and  casualty control purposes with a standardized color code. Color  code  identification  is  in  conformance  with the color scheme of table 9-1. Implementation of Table 9-1.—Valve Handwheel Color Code 9-21






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