System transition: pipe and fitting from different systems

Why a press system is one unit

A press fitting does not seal against “a pipe” but against exactly the pipe it was tested for: outside diameter with tolerance band, wall thickness, surface, material – and on the other side press profile, seal and press tool. The DVGW test and the manufacturer warranty apply to this combination. Whoever presses the pipe of one with the fitting of another leaves it, even if the nominal size sounds the same: “16” can be 16 × 2.0 or 16 × 2.2, and the 0.2 mm wall difference is, for multilayer pipe, a different inside diameter for the support sleeve.

Hence the rule: pipe and fitting come from the same system – unless the fitting manufacturer explicitly releases a third-party pipe and names dimensions for it. The two approvals we find in the documents of our contract partners are in the next sections. The flow rule (base metal first, then noble) and the material pairings are unaffected – they are on mixed installation and corrosion.

Geberit FlowFit: transition to third-party systems

For FlowFit, Geberit offers dedicated transition fittings to third-party systems in three dimensions (d 16, d 20, d 25–26), divided into seven transition groups by outside diameter and wall thickness. According to the technical information, pipes to EN ISO 21003-2 (multilayer), EN ISO 15875-2 (PE-X) and EN ISO 15876-2 (PB) are permitted; metal pipes and coated metal pipes are not. Pressing is done with the FlowFit hand press tool or the standard press jaw, and the third-party pipe is calibrated beforehand with the calibration tool of the group. Geberit points out that d and s must always be checked because of tolerances, and gives no warranty for the freedom from defects of the third-party pipe – that remains with the pipe manufacturer.

The table reproduces the Geberit list so that you can see which transition is for which pipe. The compatibility is a statement by Geberit, not a commitment by Zickwolff – we do not stock the third-party pipes, and Geberit keeps the list up to date. We check on request whether your existing pipe with its measured d × s is in the current issue. Viega takes a different route: the Sanfix P and Raxofix transition fittings (catalogue 2026) connect Viega pipe to a third-party pipe solely by its dimension d_F × s (14 × 2 to 20 × 2.5), without naming manufacturers – “only for the stated third-party pipe dimension”. Uponor and GF publish no third-party pipe list. Geberit FlowFit · Press profiles and tools.

Steel pipe systems: approval via the pipe overview

With thick-walled steel pipe the situation is reversed: there the pipe is the standard part, and the press system manufacturer states which standard pipes it presses. According to the manufacturer, Viega Megapress, Megapress S and Megapress S XL are released for steel pipes to EN 10220 with EN 10216-1 or EN 10217-1 and to EN 10255 – with wall thicknesses within the pipe overview. Which of our stock pipes are released per dimension is shown by the pipe finder in the press systems row; the approval is stored there as manufacturer data with source. Viega Megapress.

From metal to plastic – and between two multilayer pipes

Between two systems there is always a way (rule of thumb transitions are always possible): every press system has transition pieces with female or male thread, every steel pipe system has flange transitions. The transition from metal to plastic therefore usually runs via a thread – metal press fitting with male thread, plastic transition fitting with female thread – or, for large sizes, via a flange. Whoever has to join two multilayer pipes of different makes without knowing the system takes a compression fitting that works from outside and inside diameter: according to the manufacturer, Multigebo joins multilayer pipes of different makes and carries a gauge and length adjustment in the kit for that purpose.

What remains to be checked at the transition: material sequence (flow rule), seal and medium, press profile and tool of both sides – and whether the existing pipe is a pipe that any system releases at all. Joining without welding.

Mixed installation in fire protection: metal riser, plastic storey

In fire protection “mixed installation” has its own meaning: a metal pipe runs as a riser through a fire-resistant ceiling, and on the storey a combustible plastic or multilayer pipe connects. According to the manufacturers there are no recognised test procedures for this combination and therefore no general building inspectorate test certificates; the verification for a classified penetration seal is a general type approval (aBG). Viega and Geberit have obtained such approvals for their system combinations:

Before every transition: five checks

• Approval. Does the fitting manufacturer name the third-party pipe with dimensions? If not: same system or transition piece.
• Dimension. Outside diameter and wall thickness measured, not derived from the nominal size – rule of thumb FR-16.
• Material. Flow rule and pairing – mixed installation and corrosion.
• Seal and profile. Medium and temperature match the seal, profile and jaw match the fitting – press profiles and tools.
• Fire protection. If the transition penetrates a classified component, the system combination belongs to a type approval.

Further in the topic

On this topic: Mixed installation and corrosion: flow rule and material pairings · Geberit FlowFit · Viega Megapress · Press profiles and tools · Which press tool fits?

From the knowledge base: Multigebo: joining multilayer pipes of different makes · Pipe finder: released press systems per pipe · Rule of thumb: third-party pipe only by dimension table · Rule of thumb: measure the outside diameter