Rule of thumb · applies
Seal before system – why the media list means the seal
Seal before system.
A rule of thumb replaces neither the design calculation nor the manufacturer’s instructions.
- Category
- robust rule
- Standards referenced
- Manufacturers' media lists (Viega 11/2025, Sanha 2026, Geberit 07/2025, Victaulic 06.04), DIN 1988-200
Rule of thumb
First clarify medium, temperature, pressure and additives, derive the sealing element from them – and only then choose the system. Not the other way round.
Where does the rule come from?
From the mistake that shows up most often on site: the favourite system is ordered and pressed, and then the media list says its EPDM ring tolerates neither heating oil, nor steam, nor oily compressed air. The rule reverses the order because the sealing element determines the medium approval – not the pipe, not the fitting.
What is technically correct?
A press fitting seals through the elastomer ring in the bead; the metallic deformation only secures against pull-out and rotation. A system's media list is therefore the resistance list of its sealing element: EPDM for water in all its forms and oil-free compressed air, HNBR (yellow) for gases, heating oil and diesel, FKM for high temperature, solar, low-pressure steam and oil, CIIR at Geberit Mepla for drinking water and heating, nitrile at Victaulic grade T for petroleum products. The manufacturers state temperature and pressure per medium – drinking water is limited on most systems to 80 °C and 10 bar to DIN 1988-200, even if the seal would take more. Starting from the medium leads to the seal, and the seal leads to the systems that carry it.
Where does the rule end?
- It does not say which system is best – only which ones qualify. Material (flow rule, chlorides), dimension, availability and tooling decide afterwards.
- Additives are media: antifreeze, inhibitors and disinfectants change the resistance; check concentration and product against the manufacturer's media list.
- A seal cannot be swapped at will: only with the system's own replacement released by the manufacturer (e.g. FKM exchange rings for Sanpress Inox); otherwise it is a different system (Megapress S instead of Megapress, NiroSan Industry instead of NiroSan).
- Media outside the list (chemicals, foodstuffs, special cases) are to be asked of the manufacturer – the list is exhaustive.
What does the standard say?
DIN 1988-200 states the operating conditions for drinking water (up to 80 °C, 10 bar), EN 12828 for heating water; which seal may carry which medium is in no standard but in the system manufacturer's media list, which is part of the system approval (DVGW). Gas systems carry their own DVGW approvals to DVGW G 260.
DIN/EN versus ASME/ASTM
The same principle: in the USA the manufacturers likewise assign their seals (EPDM, HNBR, FKM, nitrile) per medium; the listings run through NSF/ANSI 61 (drinking water) and UL/FM (sprinklers). The ring materials are the same.
Worked example
Cooling circuit with 30 % glycol at 90 °C, plus a heating-oil line to the emergency generator. From the medium: cooling water with glycol – EPDM suitable, the manufacturer's list gives the permissible concentration; heating oil – EPDM excluded, HNBR or FKM required. The system choice follows: a stainless or carbon-steel press system with EPDM for the cooling circuit, the same manufacturer's gas system with HNBR (Megapress G, NiroSan Gas) for the heating oil – same profile, two seals, no wrong pick.
Zickwolff reference
Rule 2 of the practical rules on the press-systems hub (Martin, 24.09.2026). The system finder of the knowledge base calculates in this order: medium and temperature first, then the systems with the matching seal.
Checked today
Traffic light: applies (class A). The rule of thumb describes the logic of manufacturer approvals correctly. It does not replace the manufacturer's media list in its current edition.
Further reading
- Seals and media: EPDM, HNBR, FKM, CIIR – which medium with which sealing ring – the five sealing materials and the media matrix
- Press system finder: medium, pipe material, size – which system is approved and available? – system finder: medium and temperature first
- Press systems and joining methods: systems from Viega, Sanha, Geberit and GF at a glance – system finder, comparison, calculator – press systems overview with the practical rules
- Few systems, one profile – when the rule applies and when it does not – the sister rule on the number of systems
Frequently asked questions
Is the system value 16 bar / 105 °C enough for drinking water?
No, for drinking water the figure per medium applies – usually 80 °C and 10 bar to DIN 1988-200.
How do I recognise the seal?
By the colour code (yellow = HNBR for gas, coloured = FKM for high temperature, black = EPDM or CIIR) and by the marking on the fitting.
Can I simply swap the ring for FKM?
Only if the manufacturer releases exchange rings for this system. Otherwise the system with FKM is a different system with its own approval.
Your inquiry to Zickwolff
Send us what you have – designation, standard, quantity, date. We will clarify the rest with you.
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