Düker GmbH

Couplings for SML and other cast iron drainage pipe systems

Düker supplies couplings for all applications of cast iron drainage pipe systems. Important considerations for the selection of the correct pipe coupling, apart from the dimension, are the aggressiveness of the media (selection of the correct elastomere – standard EPDM, special version NBR), the aggressiveness of the environment (selection of the correct metal) as well as the expected pressure charge and the fixing.
The drainage pipelines being on principle pressure-free, a high expected pressure charge such as in the back water level, on waste water pumps, extended down pipes without exit requires extra measures to ensure leak tightness.
This can be done either by thrust-resistant couplings or with other auxiliary means for thrust relief, such as grip collars, abutments or similar.
For a complete overview of all couplings, grip collars etc. available from Düker please refer to the SML specifier's manual, which is offered for download on the right side of this page.


Thrust resistance and leak tightness of pipe couplings

Prüfung Druckdichtheit

Pursuant to EN 877, practically all couplings for pipelines within buildings up to DN 200 are tested with an interior pressure of up to 5 bar. However, the two pipes that are jointed for this test are tightly fixed so there are no longitudinal forces acting on the coupling. Therefore all couplings approved for cast iron drainage pipes are leak tight even under pressure, but not necessarily thrust-resistant (resistant to axial forces).


Prüfung Längskraftschlüssigkeit

Some couplings are thrust-resistant in case of inside pressure, i.e. the pipes do not slide out of the coupling due to inside pressure even if they are fixed movable.


Inside pressures can come up e.g. in


  • pipelines in the back water area
  • rain water pipelines within buildings
  • soil pipelines which run through various underground storeys without further inlets
  • pressure lines of waste water pumps

In case of insufficient thrust resistance, the use of grip collars or buttresses is inevitable. The necessary indications of the thrust resistance of couplings are to be found in the SML specifier's manual, offered for download on the right side of this page.

Downloads for couplings

SML specifier's manual (pdf, 6,864 KB)
with the complete range of couplings, installation instructions and information regarding thrust resistance and application fields



EPDM is the standard material of the rubber gasket for all metallic couplings; NBR (nitrile) is available as an optional extra for many of them. NBR is required for waste waters containing grease of predominantly animal origin, mineral oils or solvents. For all other application fields, also grease of predominantly vegetal origin, EPDM is preferable.
EPDM = ethylene propylene diene monomer rubber
NBR = acrylonitrile butadiene, nitrile rubber

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