Short answer: this glossary gathers, in alphabetical order, the technical terms that appear in data sheets, standards and rupture disc catalogs, with their English equivalent in parentheses. Each definition is written to be understood on its own.
By the technical team at P&V Control Devices · Updated October 4, 2026 · Reading time: 10 min
Go to: A · C · D · F · G · L · M · P · R · S · T · V
A
- Accumulation
- Pressure increase above the MAWP that is allowed during a discharge. ASME Section VIII generally allows 10% with one device, 16% with multiple devices and 21% in the case of external fire.
- Minimum net flow area
- Area through which the fluid passes once the disc has opened, discounting remaining petals or supports. It is used in the capacity calculation.
- Seat
- Surface of the disc holder where the disc rests and seals. Its geometry is part of the calibration.
C
- Discharge coefficient, KD (coefficient of discharge)
- Ratio between actual and theoretical flow. For rupture discs a value of 0.62 is used when the "8 and 5 diameters" rule is met.
- Back pressure
- Pressure on the discharge side of the disc. Because the disc responds to the pressure differential, back pressure raises the process pressure needed to burst it and can collapse it if it exceeds the process pressure.
- Knife blades
- Cutting elements located downstream of some reverse-acting discs, which open them when the dome reverses.
- Dome (crown)
- Domed area of the metal disc. Its orientation relative to the process defines whether the disc is forward-acting or reverse-acting.
D
- Composite disc
- Disc of two or more layers, normally a scored or perforated metal layer and a fluoropolymer seal.
- Graphite disc
- Resin-impregnated graphite disc, resistant to highly corrosive media; it is brittle and fragments on rupture.
- Reverse-acting disc (reverse buckling disc)
- Disc with the dome facing the process; on reaching the burst pressure it reverses and opens along scores or knife blades. It allows high operating ratios.
- Rupture disc (rupture disc, bursting disc)
- Non-reclosing pressure relief device that opens when a membrane calibrated to a specific pressure and temperature bursts. See what a rupture disc is.
- Forward-acting disc (tension-loaded)
- Disc with the dome facing the discharge; the metal works in tension and ruptures as it stretches.
- Non-fragmenting disc
- Disc that does not shed pieces when it opens. In practice mandatory when installed upstream of a pressure relief valve.
- Flat disc
- Domeless disc, for very low pressures or as an isolation seal.
- Rupture disk device
- Assembly formed by the disc and its disc holder, as considered by ASME.
F
- Combination capacity factor
- Factor applied to the capacity of a pressure relief valve when a rupture disc is installed upstream. If there is no certified value for that combination, 0.9 is used.
- Flow resistance factor, KR
- Dimensionless coefficient that represents the pressure loss of the open disc, as if it were a pipe fitting. It is certified by test and used in the flow resistance method (see relief area calculation).
- Creep
- Slow deformation of the metal under sustained load, accelerated by temperature. It causes premature bursts if the disc operates very close to its burst pressure.
G
- Degree of opening (opening, full opening)
- A measure of how much the disc opens. A full-opening disc leaves practically the entire line diameter free.
L
- Lot
- Set of discs made from the same material, heat, thickness and process, certified together through burst tests of samples.
M
- MAWP (maximum allowable working pressure)
- Maximum allowable working pressure of the vessel, at its top, at a given temperature. It is the reference for setting the burst pressure.
P
- Disc holder
- Component that holds and centers the disc between flanges or in the connection. See installation and disc holders.
- Operating pressure
- Pressure at which the system normally operates. It must stay below the operating ratio limit of the disc.
- Marked burst pressure
- Burst pressure shown on the disc tag, at the coincident temperature indicated.
- Specified burst pressure
- Burst pressure that the user requests in the data sheet.
R
- Score line
- Thinner line scored into the disc to control where it opens and to prevent fragmentation.
- 8 and 5 diameter rule
- Condition for using the 0.62 discharge coefficient: the disc discharges to atmosphere, is no more than 8 pipe diameters from the vessel and the discharge does not exceed 5 diameters.
- Operating ratio
- Ratio of operating pressure to burst pressure. Each disc type has a recommended maximum (on the order of 70 % to 90 %).
S
- Burst sensor (burst indicator, burst sensor)
- Device that sends an electrical signal when the disc opens, to raise an alarm or act on the process.
- Vacuum support
- Element that prevents the disc from collapsing toward the process under vacuum or back pressure.
- Overpressure
- Pressure increase above the set or burst pressure during discharge.
T
- Coincident temperature
- Disc temperature to which its marked burst pressure corresponds. The burst pressure of metal discs decreases as temperature increases.
- Burst tolerance
- Allowable variation between the actual burst pressure and the marked one. Classic ASME reference: ±2 psi up to 40 psig and ±5 % above.
V
- Pressure relief valve (safety valve)
- Spring- or pilot-operated relief device with reclosing. See rupture disc vs pressure relief valve.
Is a term missing, or do you have a datasheet with abbreviations you do not recognize? The P&V Control Devices team can help you interpret it.
Related guides: Disc types · How to select a disc · Standards