Choosing the right coupling

Start with system type - pressurised or gravity system?

Is the system pressurised or gravity fed? The answer determines which requirements the coupling must meet, so the guide splits into two paths here.

• Pressurised system - drinking water, pressure sewers and other pipelines under operating pressure.
• Gravity system - wastewater and stormwater without pressure.

2: Establish material and outside diameter

Applies to both pressurised and gravity systems. Note the pipe material (PE, ductile iron, steel, PVC, PP, concrete, vitrified clay) and the outside diameter (OD) on both sides of the joint. Many couplings can bridge different materials, but only within a specified OD tolerance range.

3: Pressurised systems - choose function

The coupling must withstand the pipeline's pressure class (PN) with margin for pressure surges. The next question is whether it also needs to be restrained.

A coupling can withstand pressure without being restrained. End-load forces occur where the pipeline changes direction or terminates, for example at bends, branches, reducers and end closures. If the pipeline is anchored there, the anchoring absorbs these forces. If it is not anchored, the coupling itself must resist them - and a restrained coupling is needed.

• Universal coupling (e.g. Hymax 2) - when the pipeline is anchored and you need to join different materials or accommodate diameter differences.
• Restrained coupling (e.g. Hymax Grip, GFIX) - when end-load forces occur and the pipeline is not anchored at the joint.
• Internal coupling (IBINLINE) - repair from inside the pipeline without trenching.

4: Gravity systems - choose function

In gravity systems the pressure is low, so the focus is on watertightness and flexibility. The coupling must seal against both leakage out and infiltration of groundwater, and cope with minor settlement and angular deviation.

• Flexible rubber coupling (Fernco) - quick joints or transitions between materials, installed without special tools.
• Open repair coupling (Fernco) - repair a damaged pipeline without cutting or dismantling it.
• Internal coupling (IBINLINE) - repair from inside the pipeline without trenching.

Not sure?

Tell us the system type, pipe type and outside diameter on both sides, and our specialists will help you choose the right model. Call 010-206 91 00 or send an enquiry.