O-Ring in ATD (Anti Telescoping Device)

The O-ring in the ATD is a key part of any membrane system filled with spiral wound modules. To find the correct O-ring for your ATD, measure the groove of your ATD first.


O-rings are put into a groove of the ATD.

The grooves should - if possible - be inserted at right angles.

O-Ring sizing

O-rings are sized by the inside diameter d1 and by the cross section d2. Example: 23,4 x 2.6 [mm]

Table: O-ring groove for ATDs

The following table applies to the “quick determination” of the O-ring groove for ATDs.
O-ring cross section d2 [mm] Gland depth D [mm] Groove width c [mm]
2.00 1.60 2.6
2.40 1.80 3.2
2.50 1.90 3.3
2.65 2.05 3.5
3.00 2.40 4.0


The built-in O-ring is deformed when pressed into the permeate tube. This deformation is associated with a change in cross-section. The compression initiates the sealing process. When the membrane system is pressurized, the pressure on the compressed O-ring increases. The O-ring returns to its normal shape when no pressure is applied. This memory is how O-rings seal under low to no pressure.

Compression [%] = 100 x (d2 - D) / D

O-Ring unpressurized

The O-ring seals when unpressurized due to its elasticity and restoring force between the two sealing surfaces. Placed in an ATD, O-rings are used to separate the (pressurized) feed section from the (unpressurized) permeate section (pressure in the feed section must always be higher as in the permeate section).

O-Ring pressurized

When pressure is applied to the system the O-ring will be pushed against the groove wall opposite the direction of the pressure. It expands perpendicular to the direction it is being squeezed by the pressure. With increasing pressure, the O-ring behaves like a highly viscous, incompressible liquid. A pressure exerted on the O-ring propagates with practically the same strength in all directions (hydrostatic law by Blaise Pascal). The seal effect of the O-ring is created by the elastic deformation of its cross-section.


- The compression for O-rings EPDM or Viton (both 70 Shore) should be in the range of 15..22%.
- The scale of the deformation of the O-ring diameter is essentially dependent on the groove depth D.
- The minimum compression required depends on the application (RO, UF).
- The maximum compression is due to the requirement of a long service life.
- Excessive compression has a negative impact on the lifetime of the O-ring.

Messinger Engineering
David Hess Weg 34
CH-8038 Zürich

T +41 79 390 60 48

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