Quick Couplings Seal Ring Material Introduction

When it comes to hydraulic quick couplings, the most important function is that the fluid does not leak when disconnecting or connecting. This brings us to the sealing material. When choosing a hydraulic quick-release coupling, the most important consideration is the body material, in addition to the working pressure. Other factors, such as the working temperature of the fluid, the corrosiveness of the fluid, etc., need to be carefully considered in the selection of the seal material. If the wrong seal material is selected, the quick release coupling will leak quickly.

In hydraulic quick coupling applications, the fluid material is often hydraulic oil, so in most cases the default seal material is NBR. For other applications, such as chemical transport, Viton (FKM) seals are often used. In some cases, FFKM is used when hydrogen sulfide is present in the fluid.

NBR – Acrylonitrile-Butadiene-Elastomer

Suitable for use in petroleum-based hydraulic fluids, glycol-based hydraulic fluids, diester-based lubricants, gasoline, water, silicone grease, silicone oil, and other media. It is the most versatile and lowest-cost rubber seal available. Not suitable for use in polar solvents such as ketones, ozone, nitrocarbons, MEK, and chloroform. The typical operating temperature range is -40 to 120 °C.

If you look carefully, there are several versions of the information on the operating temperature. From -30˚C to 100˚C, -40˚C to 120˚C, even 80˚C, and especially some websites are confusing. We have done our own experiments.  120˚C worked for 48 hours without any problem, so we chose the 120˚C version in our datasheet. However, we recommend that you do not use NBR at temperatures above 100˚C to ensure that there is no risk of leakage.

HNBR – Hydrogenated NBR Seals

HNBR has a considerable improvement in the resistance to heat, ozone, and aging, and gives it good mechanical properties. Excellent resistance to corrosion, tearing, and compression deformation, better resistance to ozone, sunlight, and weathering. It has better anti-wear properties than NBR. Suitable for use in washing machines, automotive engine systems, and refrigeration systems using the new environmentally friendly refrigerant R134a. Not recommended for use in alcohols, esters, or aromatic solutions. The general use temperature range is -40~150 ℃.

Hydrogenated NBR seals are not a common material in quick-release couplings and are only used in a few specific applications. This is because of the relatively high cost. At higher temperatures, they do not perform as well as FKM, which is mainly used for wear resistance.

FKM – Fluoroelastomer

High-temperature resistance is better than NBR, excellent weather resistance, ozone resistance, and chemical resistance, but poor cold resistance. Resistant to most oils and solvents, especially acids, aliphatic hydrocarbons, aromatic hydrocarbons, and animal and vegetable oils. Suitable for sealing needs of diesel engines, fuel systems, and chemical plants. Not recommended for use in ketones, low molecular weight esters, and mixtures containing nitriles. The general use temperature range is -20~250 ℃.

They are generally not resistant to hot water, steam, polar solvents, glycol-based brake fluids, and low molecular weight organic acids. In addition to standard FKM materials, there are special materials with different monomer compositions and fluorine content (65% to 71%) that offer better chemical or temperature resistance and/or better low-temperature performance

FFKM – Perfluoroelastomeric

FFKM is a perfluorinated rubber compound that contains more fluoride than FKM fluoroelastomers. They have better resistance to high temperatures and chemicals and can withstand even the presence of oxygen plasma for several hours. Some grades have a maximum continuous operating temperature of 327 °C for applications in contact with hydrocarbons or highly corrosive fluids, or where a wide range of temperatures are encountered. This combination of properties allows FFKM seals to reach very high UHV pressures without the need for metal seals. However, they are much more expensive than standard FKM O-rings.