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O-rings and their uses

15 February 2021 | Insights

What are the O-rings (OR)?

O-rings are perfectly circular rubber gaskets with a round section characterized by strict tolerances, both on the diameters and on the section. The O-ring is used to prevent the passage of a fluid, liquid or gas and it performs this function when it is inserted into the appropriate seat.

Sealing is generally ensured either by mechanical action alone, i.e. by pressing the o-ring into the seat; or by mechanical action associated with the pressure that the fluid applies on the ring itself.

O-rings can be produced in different materials: the main ones are NBR, FPM/FKM, HNBR, EPDM and VMQ

Uses of the O-rings and the elements characterizing the sealing

O-Rings can be used as static gaskets – sealing two fixed surfaces – or as dynamic seals between two surfaces, one of which is moving on the other.

The efficiency of the seal is directly proportional to the size of the surface where the O-ring and its seat meet. This faying surface increases as the pressure exerted on the ring increases: it either derives from the mechanical action created by blocking the O-ring in the seat, or from the action of the fluid with which the ring is in contact.
Generally, we try to exploit both to ensure that the contact surface is at its maximum. However, for fluids with low pressures, large surfaces are not necessary: sometimes a 10% compression of the ring is sufficient to obtain an efficient degree of sealing. Another factor to pay attention to is the seat where the O-ring is placed.