Page 249 - Valve Selection Handbook

236 Valve Selection Handbook

Figure 6-18. Reverse-Buckling Disc with Figure 6-19. Reverse-Buckling Disc
Partial Circumferential Score Line, Low Partial Circumferential Perforated
Pressure Series. (Courtesy ofFike Metal Score, Designed for Lowest
Products.) Pressures. (Courtesy of BS&B.)

Reverse-buckling disc of slip-away design. Reverse-buckling discs of
the slip-away design, as shown in Figure 6-20, function by being
expelled from the holder upon buckling. The relatively narrow flat seat-
ings of the disc are mounted in a recess of the inlet holding part and
sealed with an O-ring or a flat gasket. No special torque settings are
required. To prevent the disc from traveling along the vent line, the hold-
er can be provided with an integral or separate arresting device. This
allows the disc to be mounted upstream of the pressure relief valve.
Advantages of this design are the operating ratio can be up to 95%; the
reversal ratio in general is less than 1.0 with a maximum of 1.1 for smaller
sizes; and the size range is from DN 25 (NFS 1) to DN 1200 (NFS 48).
The disadvantages are it is not suitable for use in liquid-full systems
except in the larger sizes, and it may require vacuum support.

Reverse-buckling disc slotted and lined with buckling bars. The rup-
ture disc shown in Figure 6-21 consists of a slotted component that is the
actual pressure sensitive element, and a seal element of either plastic or
metal. In combination with a metal seal, the disc supports full vacuum.
The partial circumferential slot is teeth-shaped, while the tabs represent
buckling bars that control the buckling process. On reaching the buckling
pressure, the bars buckle and break off and allow the disc to hinge open.
During this process, the teeth ring cuts open the seal member.