Working Pressure

Due to our advanced manufacturing methods, Elfab is able to perform working pressure procedures unlike anything seen across the pressure relief industry. In fact, we are able to provide the following key advantages through this service:

•   The manufacture of every product to a zero-manufacturing design range (MDR). This service is provided at no additional charge.

•   Assurance of a better-than-industry-standard performance tolerance of 3% rather than 5%.

How do these advantages help users? You can work the process to a higher pressure using the same set pressure for the rupture disc. This results in shorter process times and tighter safety margins, as well as the possibility of rationalising your stock-holding inventory.

This entire working pressure procedure is best explained in the following example, based on ordering a100 psig rupture disc. The following table sets out typical parameters of what is then supplied:.

ElfabZero MDR35% MDR10% MDR
Lowest possible marked burst pressure (psig1) 1001009590
Burst pressure tolerance +/-2%3%5%5%5%
Minimum burst pressure (psig)97959085
Operating ratio 4%92909090
Maximum working pressure (psig)929085.581


The marked burst of the 100 psig rupture disc is stated in one of two ways. With the zero manufacturing design range, the marked burst is the same as the ordered burst. Alternatively, with the ten per cent manufacturing design range, the marked burst is the mean of the actual test bursts which must lie between this limit. This is demonstrated through the following points:

•    Burst pressure ordered = 100 psig +/- 5% @ 68°F. With Zero M.D.R.

•    Marked burst on disc tag = 100 psig +/- 5% @ 68°F.

•    Burst pressure ordered = 100 psig +/- 5% @ 68°F. With 10% M.D.R.

•    Actual test burst mean = 90 psig marked burst = 90 psig +/- 5% @ 68°F.


Burst pressure tolerance is the limit of the burst pressure of the disc, normally stated as a plus or minus percentage.

Manufacturing design range is the range — normally expressed as zero, minus five per cent or minus ten per cent — applied to the requested burst pressure. The mean of the test bursts carried out must lie within this range.

Operating ratio is the maximum recommended pressure that the rupture disc should be subjected to in service. Above this figure, the rupture disc will fatigue and give a reduced service life. It is stated as a percentage of the marked burst.