With the right compound, HNBR radial shaft seals deliver reliable performance in automatic coffee machines — even with regular cleaning cycles. What matters when cleaners, descalers and steam meet elastomers.
What is in coffee machine cleaners?
Most tablets and powders combine alkaline builders such as sodium carbonate, oxygen-based oxidising agents — typically sodium percarbonate, which releases hydrogen peroxide in water — and, in descalers, organic acids such as citric acid as well. These chemicals dissolve coffee oils and deposits. And they are the reason why the choice of material at this sealing point is no side issue.
Why HNBR is the sound standard choice
Peroxide-cured HNBR shows very good resistance to hot water and steam as well as to dilute acids and bases — precisely the media that occur during cleaning and descaling. The operating window is roughly −40 to +150 °C. HNBR is widely used in food environments because it tolerates the usual cleaning and disinfecting agents.
When FKM is the better choice
If the design exposes the sealing lip frequently and at high temperature to oxidising cleaners, peroxide-cured FKM is worth considering. It is expressly designed for hot water and steam, offers extended chemical resistance and, as a material, reaches about 220 °C.
EPDM for pure water and steam systems
Peroxide-cured EPDM is outstanding in hot water and steam — up to about 140 °C steam. It does not, however, tolerate mineral oils and hydrocarbons. Where lubrication is needed, only silicone greases can be used. For purely aqueous systems EPDM is therefore a good choice.
What extends service life
- Protect the seal from hard water jets. Do not direct concentrated cleaner straight at the contact zone — rinsing water should carry the residues away.
- Observe the cleaner manufacturer's dosage and cycle times and rinse thoroughly to limit the oxidative load.
- Check lubricant compatibility. Sealing lip and lubricant have to match chemically, otherwise the elastomer hardens or softens over time.
Why VR seals suit compact appliances
VR radial shaft seals use a springless diaphragm design. In comparative tests they need only a third to a quarter of the radial force of spring-loaded elements for the same sealing performance. That lowers friction losses and heat — a noticeable difference in small drives and tight installation spaces.
Selection at a glance
- HNBR, peroxide-cured: hot water and steam, dilute acids and bases, −40 to +150 °C. The standard choice for most sealing points in an automatic coffee machine.
- FKM/P, peroxide-cured: hot water and steam, broader chemical and oxidative resistance, up to about 220 °C. For aggressive cleaning media.
- EPDM, peroxide-cured: excellent in hot water and steam up to about 140 °C, but no oils. Use silicone grease only.
All the materials named are available in certified food quality. The details are in the elastomer overview.