Aluminium seals

How to select the size

Size means inner diameter, outer diameter and thickness. The inner diameter must match the bore, not the thread.

Aluminium does not tolerate re-torquing: once deformed it will not recover.

Materials

The material is chosen by medium and temperature, not by price:

• NBR — the standard for mineral oil, −30…+100 °C. Most common and least expensive.
• FKM (Viton) — up to +200 °C, aggressive media, brake fluid. Three to five times the price of NBR.
• PU (polyurethane) — high pressure and abrasion, but not above +80 °C.
• PTFE — chemicals, very low friction, but poor under compression without support.
• EPDM — water, steam, glycol-based brake fluid. Not compatible with oil.

Common fitting mistakes

Three mistakes that make a new seal leak within a day:

1. Damaged lip during fitting. The seal is pushed over threads or splines without a sleeve — the lip is cut and you cannot see it.
2. Measuring a worn part. The old ring has lost its shape, so the new size does not seat in the groove.
3. No back-up ring. Above 160 bar the seal extrudes into the gap.

Frequently asked questions

Aluminium or copper?
Aluminium where the seating face is rough or damaged and pressure is moderate. Copper for high pressure and temperature.

Can an aluminium washer go on a steel fitting?
Yes. There is no damaging galvanic couple here — aluminium is softer and acts as a consumable.

Are non-standard sizes available?
The standard range is in the table; non-standard sizes on request with a drawing.