An FKM ring – where EPDM is no longer enough
FKM, usually called Viton in everyday use, is the tougher relative of ordinary sealing rubber. The material withstands higher temperatures, does not swell in oils and greases and hardens more slowly. That is exactly why the manufacturer explicitly specifies it for certain sealing points – and why it pays to look not at a dimension here, but at the number.
With an inner diameter of 11.89 mm, this ring is very close to other positions in the same series. Side by side on the workbench they are almost impossible to tell apart, and that is precisely the trap: the wrong ring can be fitted and seals for a few weeks. Then the dripping starts all over again.
When it is due
A fitting drips even though it is tight. The removed ring is hard, discoloured or swollen. It has lost its round cross-section. Or the sealing point is being opened anyway – in which case a new ring always goes in, and the old one never goes back.
At a glance
| Type |
FKM O-ring, often referred to as Viton |
| Location |
Sealing point inside the machine; our documentation does not state the exact position |
| Fits |
Order by part number; our documentation does not name a single model |
| Scope of delivery |
1 O-ring |
| Part number |
H.1.047 |
| Version |
Cross-section 1.78 mm, inner diameter 11.89 mm, FKM, hardness 70 ShA |
| Installation |
Fitting by a qualified technician recommended |
| Brand |
La Marzocco |
Important for installation
The ring sits inside the machine at a pressurised point. Depressurise the machine, check the sealing surface, then test for leaks – in that order. We do not give step-by-step instructions, because we do not know the installation point and because nobody should turn pressurised fittings on a hunch. If in doubt, the replacement belongs in a workshop.
Who it is for
For technicians who work with the service documentation and read H.1.047 there. And for businesses that keep their seal stock strictly sorted by type: anyone who keeps EPDM and FKM apart has significantly fewer repeat repairs.
What goes with it
From the same series, but in a different material, comes the O-ring 1.78 × 10.82 mm in EPDM; the O-ring 1.78 × 20.35 mm in EPDM is also a separate position. Another Viton part is the group cover gasket in Viton. All the small parts are in the Original spare parts category, and the brand's range in the La Marzocco accessories and spare parts category.
From our workshop in Bern and Zurich: We do not measure O-rings with a ruler; instead, we lay the old ring flat on a sheet of graph paper and read the inner diameter against the scale. At 10.82 versus 11.89 millimetres, exactly this difference decides between sealed and not sealed – you cannot get it right by eye alone. Our own routine, not a manufacturer specification. And because sealing work takes patience, we have Cozy Chocolate running alongside. For the test shot at the end we use Very Nutty; everything else is in Coffee beans.
No returns
Original spare parts are excluded from exchange and return. They are sourced specifically for each order and cannot be resold after being fitted or test-fitted on the machine. So before ordering, check the model, year of manufacture and serial number of your machine – or drop us a quick message and we will clarify the fit together. Your statutory rights regarding defective goods remain unaffected.
Frequently asked questions
Is FKM the same as Viton?
Viton is a brand name for FKM. The material is the same type; the name comes from industry.
Can I use an EPDM ring instead?
If the manufacturer specifies FKM, there is a reason. EPDM behaves differently with oils and at higher temperatures. Stick to the number in your documentation.
Where does the ring sit in the machine?
Our documentation only lists position H.1.047, without an installation location. We will not make one up. Tell us where the number appears in your service documentation and we will match it up.
How do I tell it apart from the EPDM ring?
By the dimensions and the number, not by the colour. That is why we always store O-rings individually with their number.
Can I take a look at the part at your place?
Yes. Come to our showroom in Bern at Gerberngasse 44 or in Zurich at Hagenholzstrasse 50b. Bring the old ring with you and we will measure it together.
Questions about the material? Write to us at [email protected]. We deliver across Switzerland and to Liechtenstein in 2-4 working days.
