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238                  Valve Selection Handbook

               The  disc  is  made in  sizes  DN25  (NFS  1) through  DN  600  (NFS  24).
            The burst pressure range covers the lowest burst pressures  up to  120 barg
            (1800  psig)  at  22°C  (72°F)  operating  temperature.  Maximum operating
            temperature is 550°C  (1000°F).
              The  advantages of this disc  are zero  manufacturing range,  burst toler-
            ance is down to plus/minus 2%, operating ratio is as high as 95%, and it
            may be employed in liquid-full  systems (consult manufacturer).

            Two-way   rupture  disc.  In  the  case  of  domed  two-way rupture  discs,
            such  as  shown  in Figure  6-22  and  Figure  6-23,  flow  in one  direction  is
            forward  acting and in the other direction reverse acting.
              The  rupture disc  shown  in  Figure  6-22  consists  of  three  components.
            The upper perforated  component  is a forward-domed rupture disc  that is
            provided with a partial circumferential score line and protects the pressure
            system against overpressure.  The  second  element  is a PTFE  seal  member
            that fails under overpressure  and subnormal pressure  conditions. The third
            element is represented  by a reverse-buckling  bar disc that fails on subnor-
            mal pressure.  On rupture of the  upper  component,  the buckling bars will
            fail in tension and allow the disc to open in unity with the upper disc.































            Figure 6-22.  Two-Way Rupture Disc Incorporating Buckling Bars. (Courtesy of  Rembe
            GmbH.)
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