To verify the mathematically simulated test results, the 30-in. filter elements (i.e., A, B, C, D, and E) with no break in
integrity were installed into the multiround housing and tested with the bubble point and multipoint diffusion tests. All
cartridges were tested three times and rinsed between each test (see Figure 2).
Figure 2: Multiround housing 5 x 30-in. cartridges A, B, C, D, and E. (ALL FIGURES ARE COURTESY OF THE AUTHORS.)
One 30-in. cartridge (cartridge E) was then replaced by a 20-in. cartridge. A 10-in. filter housing, containing the bubble-point
failing cartridge, was connected in parallel with the multiround housing, consequently representing a five-round 30-in. setup
in terms of membrane surface. The system containing cartridges A, B, C, D, F, and G was tested with bubble-point and multipoint
diffusion tests. All cartridges were rinsed between each of the three tests (see Figure 3).
Figure 3: Multiround housing and 10-in. housing, 4 x 30-in. cartridges A, B, C, and D; 1 x 20-in. cartridge F; and 1 x
10-in. cartridge G or H. ( (ALL FIGURES ARE COURTESY OF THE AUTHORS.)
The bubble-point failing cartridge (cartridge G) in the 10-in. housing was then replaced by the high-diffusion cartridge (cartridge
H), and the same tests and rinses were performed. Instead of performing a separate single-point diffusion test at 2500 mbar
(36.25 psi), the authors considered the diffusion value at the same pressure during the multipoint diffusion test was representative.
Individual test result
The expected difference in diffusion between five 30-in. cartridges (i.e., A, B, C, D, and E) (137.9 mL/min) without loss
of integrity and an equivalent setup including the bubble-point failing 10-in. cartridge (i.e., A, B, C, D, F, and G) (139.4
mL/min), at the standard test pressure of 2500 mbar (36.25 psi) was <2 mL/min, thus being not possible to detect with a high
degree of confidence.
An equivalent setup including the failing 10-in. high-diffusion cartridge (i.e., A, B, C, D, F, and H) would require the maximum
allowable diffusion value to be lowered by more than 40% as compared with the cumulated individual maximum diffusion values
to be detected at all. Using such a high safety margin creates a high potential risk of getting false-failure test results
with filters that otherwise have no break of integrity.
Based on the typical diffusion profile of a cartridge with no loss of integrity, it was possible to define a maximum allowable
diffusion curve, which made it possible to get a clear multipoint-diffusion test failure when the bubble-point failing 10-in.
cartridge was included in a multiround setup (cartridges A, B, C, D, F, and G). The same approach showed that it should be
possible to get a clear test failure when having the 10-in. high-diffusion cartridge in a multiround set-up (cartridges A,
B, C, D, F, and H).