EPDM O-rings: water, steam and brake fluid

What are EPDM O-rings?

O-rings made of EPDM, ethylene propylene diene rubber, are ideally suited to contact with hot water and steam. Whether in the sanitary and heating sector or in the food industry: EPDM O-rings offer the necessary durability and, where required, the industry-specific approvals for these challenging fields of application.

The good media resistance also makes EPDM suitable for use in cooling circuits or pressure systems, not least in the automotive industry. Many practitioners also know EPDM under the trade names of global suppliers such as Keltan®, Vistalon®, Dutral® or Nordel®.

The most important alternatives to EPDM O-rings are the materials NBR and FKM.

The 5 most important advantages of EPDM O-rings

EPDM O-rings are subject to a wide range of stresses from mechanical loads, temperatures, media or simply the environment. In some areas, these act even before the operating conditions of the sealing point come into play. For example, ozone in the ambient air can attack O-rings while they are still waiting to be used in the equipment store. NBR O-rings in particular must be handled very carefully in this respect. With O-rings made of EPDM, however, this risk does not exist, because the material is susceptible to neither solar radiation nor ozone.

This not only makes storage unproblematic but also enables outdoor use of the sealing elements. The high abrasion resistance also allows use for dynamic seals in which the sealing surfaces are in motion. Like NBR, FKM or CR, EPDM O-rings withstand mechanical loads. A broad media resistance profile and many material approvals for special applications make EPDM O-rings almost universally applicable. The fields of application include the food and drinking water sectors, which place high demands on the safety of the sealing materials.

The 3 most common fields of application for EPDM O-rings

Cooling water and heating circuits

Glycol is found in many technical media because it can lower the freezing point of water to as low as −55 °C. Brake fluid or engine coolant are two application examples from the automotive sector. Thanks to their pronounced resistance to water and glycol across a wide temperature range, EPDM O-rings are particularly well suited to sealing such systems.

Sealing elements made of EPDM reliably seal the connection points of components such as radiators, lines, thermostats or pumps. In these safety-critical applications in the automotive sector, EPDM is generally given preference over alternative materials. Only when contact with mineral-oil-based media cannot be ruled out is the more cost-intensive material FFKM used.

Food and pharmaceuticals

Food and medical products enter the human body directly, so unwanted interactions must be absolutely ruled out. Those responsible must ensure the flawless condition of the products throughout the entire production chain. O-rings in the production plants must therefore function reliably in order to rule out contamination.

At the same time, the sealing elements must not affect the products in direct contact. EPDM is tasteless and odourless as well as inert. Many grades of EPDM O-rings with FDA or USP approvals are completely free of plasticizers. EPDM O-rings also withstand the aggressive conditions of cleaning and sterilization procedures.

Pressure fluids

Pressure fluids are responsible for transmitting force in hydraulic systems. Until now, mainly mineral-oil-based media have been used here. However, their unintended contact with the environment poses an ecological problem. For this reason, there are growing demands for the use of biodegradable pressure-transmission media.

These changed requirements must of course also be transferred to the remaining components of the hydraulic systems. EPDM O-rings are suitable not only for conventional media such as brake fluid DOT 3 and DOT 4, but also for the more environmentally friendly alternative HEPG (polyalkylene glycol) in accordance with DIN ISO 15380.

What is the media resistance of EPDM O-rings?

EPDM O-rings are resistant to hot water and steam. This also explains the preferred use of the material in sanitary and drinking water systems. In addition, EPDM O-rings withstand contact with glycol-based brake fluids at high temperatures. Many organic and inorganic acids also belong to the resistance profile of the sealing material.

Also particularly worth highlighting is the insensitivity of EPDM to ozone and weathering influences. Its suitability for weather-exposed outdoor use and the long possible storage times without special precautions make handling EPDM O-rings particularly uncomplicated in practice. These qualities contribute considerably to the suitability of EPDM for automotive engineering.

The most significant gap in the resistance list of EPDM O-rings, however, is products based on mineral oil. Lubricants or oils cause the material to swell. As a result, there is a considerable reduction in hardness and break-outs with rounded edges. This weakening of the material causes EPDM O-rings to lose their sealing effect. EPDM is therefore not suitable in combustion engines for areas that carry coolant but also come into contact with mineral-oil-based lubricants.

How high is the EPDM temperature resistance?

EPDM is a versatile elastomer that is known in particular for its high temperature resistance. The specific temperature limits depend on composition and processing. The decisive factor above all is the type of cross-linking.

In special applications, EPDM can exhibit even higher temperature resistance. In contact with water, it withstands temperatures of up to 170 °C, while in air it can withstand up to 150 °C. For steam applications, there are specific EPDM compounds that can withstand temperatures of up to 200 °C. At temperatures above 200 °C, however, other materials such as perfluoroelastomer (FFKM) must be used.

In the food and beverage industry, peroxide-cured EPDM with FDA approval is frequently used as a sealing material. The temperature resistance of EPDM in this sector is typically between −50 °C and +150 °C.

What are the mechanical properties of EPDM O-rings?

EPDM is a synthetic rubber produced by the polymerization of three monomers. By adjusting the proportions of the monomers and other additives, the chemical and mechanical properties of the products can be set according to requirements. In principle, this gives EPDM very high elasticity, which is largely responsible for the reliable sealing effect.

Even after prolonged compressive load, EPDM O-rings return almost completely to their original shape. This elasticity can be increased even further by peroxide cross-linking instead of the standard sulfur cross-linking. In terms of abrasion resistance, EPDM, together with NBR, CR and FKM, is well ahead of silicone-based sealing materials. This enables dynamic use, in which the moving sealing surfaces cause increased friction.

Other important mechanical properties worth mentioning are the high mechanical strength and the elongation at break. EPDM O-rings can be stretched considerably during the installation process, for example, without causing permanent damage. This makes installing an externally sealing O-ring particularly unproblematic.

What do I need to consider when designing the groove for an EPDM O-ring?

The temperature-related shrinkage and expansion behaviour of EPDM is not very pronounced. Therefore, no special precautions for expansion need to be taken in the groove design. For many standard applications, a compression of 25 % is recommended.

What should be considered when installing EPDM O-rings?

A few basic rules apply during installation so that the O-ring reaches the groove undamaged:

Frequently asked questions