Page 260 - Valve Selection Handbook
P. 260
Rupture Discs 247
Figure 6-33. Double Disc Assembly
with Product Leakage Warning
Devices Consisting of Pressure
Gauge and Excess Flow Valve.
(Courtesy of Sempell A.G.)
The ASME Code does not deal with double disc assemblies.
Quick-opening device. By lowering the rating of the rupture discs in a
double disc assembly to below the operating pressure, the assembly may
be used as a quick-opening device. One method of initiating quick open-
ing is to pressurize the space between the discs until the outlet disc
bursts. The operating pressure will then burst the first disc within milli-
seconds. The second method requires the maintenance of a pressure of
approximately half the normal system pressure. On dumping this pres-
sure, both discs open simultaneously within milliseconds.
When employing the second method, the following limitations apply:
• The pressure between the rupture discs cannot exceed the operating
pressure unless the rupture disc facing the operating pressure is fitted
with a back-pressure support.
• The burst pressure of either rupture disc, including burst tolerance, can-
not be greater than the operating pressure.
For conditions of both rupture discs being identical, the following
pressure relationships exist:
where Pj = normal gauge operating pressure
P 2 = gauge fluid pressure in space between rupture discs