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O-Ring Types and O-Ring Material Makeup - A Guide

02 Nov.,2022

Guides

One type of O-ring material

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O-rings are a form of gasket or seal that features a round cross-section. They are commonly used to prevent leaks of either fluids or gases from occurring in products, systems, or machinery and find use across a variety of industries. Because of their low cost, simple production process, ease of installation, and pressure resistance, they have found application in a lot of common products, such as automobiles and engines. The aerospace industry uses o-rings in many types of rockets and aircraft applications.

This article will review information on the types of o-rings and material options available, along with their suitability for different applications.

Selection Factors

The fact that o-rings can function in so many applications is largely attributable to the fact that there is a wide range of materials available from which they may be fabricated. This range of selection allows the designer to consider the properties of the material and select a suitable option based on how well that material performs against the expected operating conditions of the application. The factors that are usually considered when selecting a material for an o-ring include:

The material’s compressibility or hardness (durometer)
The performance against environmental and operational conditions, including:
- Oils
- Solvents
- Acids
- Bases
- Steam
- Fuels
- Corrosive chemicals
The abrasion performance of the material
The permeability of the material (permeation)
The cost of the material

O-rings are usually produced from some form of elastic polymer or elastomer. These polymers are cured, often through vulcanization, resulting in improved strength, durability, and elasticity. Different materials have different properties, though, with some exhibiting greater elasticity and others possessing more tear-resistance.

O-Ring Materials and Types

Below is a summary of the different commonly used o-ring materials and types.

Because of the range of materials available, determining which O-ring is appropriate for use in a specific application is a process whose importance cannot be overstated. The information below, along with consultation with the resources offered by o-ring manufacturers and suppliers can assist designers and engineers with narrowing the options and making an informed decision for their project. The materials covered below include:

Static and Dynamic O-Ring Sizes and Groove Dimensions

Image credit: Allied Metrics

Nitrile (Buna-N)

Temperature range: The nitrile O-ring temperature range is between -65 degrees Fahrenheit and 300 degrees Fahrenheit.
Suited for: General purpose seals, such as petroleum oils, water, and some hydraulic fluids. Buna-N is also resistant to tears and abrasive treatment.
Avoid: Buna-N can have problems with automotive brake fluid, ketones, phosphate ester hydraulic fluids, and nitro and halogenated hydrocarbons. While it is ozone and weather-resistant, this resistance is not infallible but can be supported through compounding.
Applications: Nitrile functions well in applications that have limited temperature and resistance requirements.

Ethylene Propylene Rubber (EPR)

Temperature range: Between -65 degrees Fahrenheit and 300 degrees Fahrenheit.
Suited for: Skydrol, a hydraulic fluid, has a noxious smell and can irritate the skin, and its corrosive properties can be damaging to equipment. EPR o-rings work well with Skydrol and other hydraulic fluids, as well as steam, water, silicone oils, brake fluids, and alcohol.
Avoid: Similar to nitrile, EPR is not perfect for a wide range of applications due to wear and tear issues.
Applications: The aerospace industry uses EPR o-rings in hydraulic pumps.

Fluorocarbon (Viton)

Suited for: Fluorocarbon is an all-around material that can handle a number of applications, especially diverse sealing jobs that involve movement. It is also suited for petroleum oils, silicone fluids and gases, acids, and some halogenated hydrocarbons, like carbon tetrachloride.
Avoid: Fluorocarbon is not recommended for Skydrol, amines, esters, and ethers with low molecular weight and hot hydrofluoric acids.
Applications: Fluorocarbon o-rings are very versatile, and features in many different automotive, appliance, and chemical processing industries.

Neoprene

Temperature range: The neoprene O-ring temperature range is between -65 degrees Fahrenheit and 300 degrees Fahrenheit. Types of O-ring seals.
Suited for: Neoprene can seal refrigerants in refrigeration and air conditioner units, as well as petroleum oils and mild acid resistance silicate ester lubricants.
Avoid: Finished neoprene products are often compounded with lead-based agents, which can be hazardous to human health. Additionally, some people are allergic to basic neoprene. In a functional sense, it is not very resistant to petroleum lubricants and oxygen.
Applications: Neoprene functions well in refrigeration units of air conditioning systems.

Types of O-ring seals

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Polyurethane

Temperature range: Between -65 degrees Fahrenheit and 212 degrees Fahrenheit.
Suited for: Polyurethane features abrasion and extrusion resistance, as well as general toughness.
Avoid: Applications requiring good compression and heat resistance would not be suitable for polyurethane.
Applications: Polyurethane o-rings are often used for hydraulic fittings, cylinders and valves, pneumatic tools, and firearms.

Silicone

Temperature range: Between -120 degrees Fahrenheit and 450 degrees Fahrenheit, although silicone o-rings have been shown to withstand -175 degrees Fahrenheit during short periods of exposure.
Avoid: Silicone exhibits poor tear resistance, abrasion, and tensile strength. The poor abrasion resistance means they are better suited for static applications than dynamic. They do perform well with water, steam or petroleum fluids, either.
Applications: High-temperature fuel injection ports can use silicone o-rings.

PTFE

Temperature range: Between -100 degrees Fahrenheit and 500 degrees Fahrenheit.
Suited for: Pure PTFE o-rings are very rigid and hard to apply, but PTFE encapsulated o-rings handle surface wear well, in addition to exhibiting corrosion and abrasion resistance, non-permeability, chemical inertness, and low absorption.
Avoid: Like silicone, PTFE is rigid and is better suited to static applications.
Applications: Examples of PTFE o-ring uses include automotive steering devices and paint guns.

FFKM

Temperature range: Between 5 degrees Fahrenheit to 625 degrees Fahrenheit.
Suited for: Applications, where there is a high cost of maintenance or downtime, where high-temperature resistance is needed, where high chemical resistance is needed, or low outgassing is a requirement.
Avoid: Not suitable for use with molten metals, gaseous alkali metals, or halogenated freons/fluids.
Applications: Oil & Gas, Life Science and Medical applications, Food & Beverage manufacturing

Ethylene Propylene (EPDM)

Temperature range: Between -65 degrees Fahrenheit to 300 degrees Fahrenheit.
Suited for: Applications with exposure to sunlight, ozone, weathering, hot water, stream, automotive and aircraft brake fluids, some acids and bases, ketones, alcohols, plumbing applications.
Avoid: EPDM is not suitable for use with petroleum oils, fuels.
Applications: Life Science Industry, Pharmaceutical & Medical applications, Food & Beverage manufacturing, Drinking water applications.

Fluorosilicone

Temperature range: Between -90 degrees Fahrenheit to 350 degrees Fahrenheit.
Suited for: Applications with exposure to jet fuel, dry heat, some petroleum-based solvents, chlorinated solvents.
Avoid: Ketones such as MEK, Phosphate esters, some acids, automotive and aircraft brake fluids, ammonia
Applications: Aerospace, Automotive, and Chemical Industries.

Summary

This article reviewed the different types and material options available for o-rings as well as the considerations for their selection. For information on other topics, consult our additional guides or visit the Thomas Supplier Discovery Platform where you can locate potential sources of supply for over 70,000 different product and service categories, including over 1,200 suppliers of o-rings.