BS&B Pressure Safety Management LLC Releases Industry Leading Rupture Disk / Safety Relief Valve Combination Capacity Factors

New Certified Combination Capacity Factors as high as 1.0 apply to BS&B rupture disk devices.

International Codes & Standards permit the use of a rupture disk device at both a safety relief valve inlet and outlet. This combination is long recognized by the ASME Boiler & Pressure Vessel Code in the United States whose Section XIII Code provides the current means for certifying the flow capacity of this combination of pressure safety devices.

The use of rupture disk devices combined with safety relief valves continues to grow driven by the user benefits of valve inlet isolation under normal operating conditions. Benefits include:

  • Optimal leak tightness
  • Increased operating pressure ratio
  • Extended valve life
  • Reduced valve maintenance
  • Improved corrosion resistance
  • Viscous media compatibility
  • Increased reliability

Using a rupture disk device at the valve outlet will isolate the valve from super-imposed back pressure in systems where the valve does not vent to atmosphere, but rather to a manifold system. A downstream rupture disk device and valve combination will also prevent potentially corrosive gasses from the manifold system reaching the valve internals.

Combination Capacity Factors

When a rupture disk device is installed between a safety relief valve and the pressurized equipment, the flow capacity of the combination of the rupture disk and valve must be considered. This is an important relief system design consideration for the specifier and user.

ASME Section XIII describes a method for establishing the combination capacity, using specific rupture disk types with specific safety relief valve types, resulting in a ‘certified combination capacity factor’ (CCF). Where CCF’s are not available, a default factor of 0.9 may be applied to the pressure relief valve rated capacity. BS&B has established CCF's for many rupture disk device types tested with the products of many manufacturers of safety relief valves. This information is posted here: 77-1006A Flow Coefficients

Of particular interest to piping design engineers are rupture disk device and safety relief valve combinations with a CCF of 1 which means the full stamped capacity of the safety relief valve is maintained when combined with the rupture disk device. The table below shows the BS&B range of safety relief valves and rupture disk combinations with a CCF of 1.


Combination Capacity for Model 6400 Safety Relief Valve
Model Minimum Size (NPS) Minimum Set Pressure (Psi) CCF
FRS 1 100 1.0
JRS 1 100 1.0
S-90 1 100 1.0
SKr 1 100 1.0
SRD-L 1 100 1.0

A CCF of 1 allows for optimum sizing of valves and pipework minimising capital costs from the design stage. As regulations and practices tighten regarding fugitive emission control, particularly leakage through safety valves, the ability to isolate a safety valve with a rupture disk device; without adversely impacting valve capacity is gaining significance. With a CCF of 1, retrofits of rupture disk devices in the field become possible without increasing valve and pipework sizes.

BS&B is a global manufacturer of pressure relief equipment, including rupture disk devices, safety relief valves, specialty valves, pressure vacuum valves and explosion vents. Please contact us through to discuss your pressure relief needs.