FLEXNORM® Tubular Membranes For 90 mm O.D. Diffuser Bodies

Material specification

FLEXNORM® is an ethylene propylene diene monomer (EPDM) elastomer

Colour Black
Shore hardness DIN 53505 A 45 +/-5
Maximum service temperature 80 °C / 176°F
Tear propagation resistance ISO 34-1 A ≥ 10 N/mm


Dimensions / FLEXNORM® tubular membranes
Article designation Article number A Active membrane length B Overall length D Inner diameter Material Colour
MB FLEXNORM® 1000 90mm 3401000090 1000 mm / 39.37" 1060 mm / 41.73" Ø 92,5 mm / 3.64" EPDM black

Slit pattern and slit size

The tubular membrane is perforated by a specially configured pattern of slits. It has no perforation at its 6 o’clock and 12 o’clock positions as well as on both ends. The slit size is dimensioned in accordance with the specific diffuser type and application at hand. Slit sizes are available in the following range:

0,6mm / 0.024"

1,0mm / 0.039"

1,2mm / 0.047"

1,4mm / 0.055"

2,0 mm / 0.079"

Pressure drop vs. throughput for FLEXNORM® membranes in new condition with different perforation grades

The diagram above is a plot of maximum diffuser pressure drop (i.e. the pressure drop used for blower dimensioning) as a function of air throughput for different perforation grades. The pressure drop data applies for diffusers and membranes in new condition. The actual pressure drops across new diffusers/membranes will be lower and can vary in a given delivery lot within a window of 6 mbar (0.09 psi).

For example, a 1.4 mm thick FLEXNORM® membrane used at an air throughput of 15 m³/h will have:

a maximum pressure drop (i.e. the pressure drop used in blower dimensioning) of: 60 mbar (0.87 psi) and a pressure drop window within the lot of e.g.: 50 – 56 mbar (0.72 – 0.81 psi).

The pressure drop across a diffuser or membrane can change in subsequent operation. The amount of change depends on the purity of the inlet air, composition of the wastewater treated, process chemicals used and their concentrations as well as the aeration process technology and process conditions.

Due to these many variable factors, we cannot specify the increase in pressure drop to be expected in actual operation in your WWTP. We will however gladly advise you in accordance with our experience and develop, using your input parameters, operating conditions and maintenance plans which reduce pressure drop build-up.