Page 230 - Valve Selection Handbook

Rupture Discs 217

ever, there are many applications where rupture discs are likely to per-
form better than pressure relief valves. These include:

• Under conditions of uncontrolled reaction or rapid overpressurization
in which the inertia of a pressure relief valve would inhibit the required
rapid relief of excess pressure.
• When even minute leakage of the fluid to the atmosphere cannot be
tolerated at normal operating conditions.
• When the fluid is extremely viscous.
• When the fluid would tend to deposit solids on the underside of the
pressure relief valve disc that would render the valve inoperable.
• When low temperature would cause pressure relief valves to seize.

Rupture discs may serve special requirements by mounting two discs
in series, or in parallel, or in series with pressure relief valves

1. Two discs in series:
When the process fluid may corrode the first disc, causing the
discs to leak, the second disc prevents the leaking fluid from escap-
ing to the surroundings. However, should the first disc burst prema-
turely, the second disc is likely to burst also.
They also serve as a quick-opening device. By appropriately
choosing the burst pressures and pressurizing the space between the
discs, dumping the pressure between the discs will cause the discs
to burst within milliseconds.
2. Rupture disc in parallel with a pressure relief valve:
Rupture discs may be used in parallel with pressure relief valves
to serve as a secondary pressure relief device that is set to protect a
pressure system against overpressure excursions.
3. Rupture disc in series upstream of a pressure relief valve:
Rupture discs in series are used

• To prevent corrosive fluid from leaking into the valve. This
may allow the valve to be made of standard construction mate-
rials.
• To prevent leakage past the disc of the pressure relief valve to
the atmosphere or vent system.
• To prevent deposits from forming around the valve seat that
would impair the operation of the pressure relief valve.
• To reduce the cost of maintaining the pressure relief valve.