Česky Česká verze

O-ring

The O-ring is the most versatile packing element:

  • It is self-packing, simple, does not require big space,
  • It features double-action packing,
  • It is simple to install,
  • It is used both in static and dynamic applications - it prevents undesirable liquid leak or loss; this, however, being influenced by selection of a correct installation and material.

Drawing:

Dimensions:

The O-ring's size is defined by the d1 inside diameter and by the ring's d2 thickness. O- ring's ø d1 x d2
When specifying the O- ring's cross-section it is suitable to select the biggest cross-section, which is possible for a given case, as regards design.

The installation space dimensions must meet the following conditions:

  • Permissible elongation of the d1 inside diameter is 6 % (exceptionally 8 %) and its permissible depression is 3 % (exceptionally 4 %);
  • Upon packing of fixed parts, the d2 diameter must be reduced at least by 10 %, for packing axially moving parts at least by 6 %. Maximum permissible compression is 25 %.

Radial installation (static and dynamic)

On sealing by inside diameter it is recommended to select such O-ring size so as the difference of the d1 inside diameter and of the d4 tight diameter be as low as possible. On sealing by outside diameter it is suitable to select such O-ring size so as the d1 inside diameter be equal to or smaller than the d3 groove diameter.

Sealing by inside diameter
Sealing by outside diameter

Axial installation (static)

In the case of the O-ring's installation, considered should be first of all the direction of the pressure incidence. On application with inside pressure it is suitable that the O-ring's dimensions be by 1 to 2 % higher than the d5 groove diameter. For packing of inside pressure the O-ring is designed by 1 to 3 % smaller than the inside diameter of the d6 groove.

Inner pressure
Outer pressure

Specification of materials:

Material Temperature range Usage Hardness
NBR
Acrylnitrile-Butadiene-Rubber
- 30 °C + 110 °C standart material for hydraulic and pneumatic compression fluid on mineral-oil base
animal and vegetable oils
heavily inflame fluids, aliphatic hydrocarbons (propane,butane,gas)
silicon oils
water up to +80°C, air, bio-oils, from synthetic ester and vegetable oils
60 - 90
EPDM
Ethylene-Propylene-Dien-Rubber
- 60 °C + 150 °C hot water, vapour, brake fluid, washing means alcohols, ketones, KFZ-cold water heavily inflame fluids on the phosphorus-acid base organic and anorganic acids and bases 70
Silicone - 70 °C + 230 ° hot air, oxygen, ozone, UV-rays aliphatic engine and transmission oils, animal and vegetable oils brake fluids 70
FPM
Fluorine-Rubber
- 20 °C + 260 °C mineral oils aliphatic, aromatic and chlorine hydrocarbons gas, super-gas, diesel-propellants heavily inflame fluids on phosphate-ester base, silicon oils acids, lyes 80
AU
Polyurethane
- 25 °C + 80 °C mineral hydraulic oils
mineral engine and transmission oils gas, diesel aliphatic hydrocarbons and air
90

O-ring hardness

- It is determined in particular in accordance with the height of operation pressure and dimension of packed groove,

- For high pressure and big seam harder materials are selected so as to prevent it from being impressed into the seam.

Classification of O-rings in accordance with their application

Static sealing

Static sealing is of such a kind where mutually packed parts do not move.

- Sealing under screw-head
- Sealing for pipe joints
- sealing of lids

Dynamic sealing

In the case of a moving sealing, mutually packed parts move axially, helically, oscillate, or rotate.

The most widespread use:
- hydraulic and pneumatic devices requiring small installation space
- for low strokes and relatively small diameters

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