Seal materials selections important for Quick Coupling
Choosing the correct seal material for the O-ring of quick couplings are really important because the quick couplings will be used in a different environment, with different fluids and temperature. The wrong seal material will make the quick coupling leak. To choose a correct seal material, one needs to think about the operational performance such as working pressure, fluid material, working temperature, etc. O-ring selection is based on chemical compatibility, application temperature, sealing pressure, lubrication requirements, durometer, size, and cost.
Seal Materials Options
There are types of seal materials options for quick couplings as our experiences. And some seal materials are not in our supply, because they are from the special manufacturer, like the parker.
- Nitrile rubber – we usually call it NBR or Buna-N, is a common material for O-rings because of its good mechanical properties, resistance to lubricants and greases, and relatively low cost. The physical and chemical endurance of NBR materials is determined by the acrylonitrile (ACN) content in the base polymer: low content guarantees good flexibility at low temperatures, but limited resistance to oils and fuels. With the increase of ACN content, low-temperature flexibility decreases and oil resistance improves. The physical and chemical resistance of NBR materials is also affected by the polymer curing system. Compared with the sulfur donor cured materials, the peroxide-cured materials have better physical properties, chemical resistance, and thermal properties. Standard grades of NBR are generally resistant to mineral oils and greases, many grades of hydraulic oils, aliphatic hydrocarbons, silicone oils and greases, and about 176°F(80°C) of water. NBR is generally resistant to aromatic and chlorinated hydrocarbons, fuels with high aromatic hydrocarbon content, polar solvents, alcohol-based brake fluids, and non-flammable hydraulic fluids (HFD). NBR also has low ozone resistance, weathering resistance, and aging resistance. HNBR has obvious heat resistance, ozone resistance, and aging resistance, and has good mechanical properties.
- Fluoroelastomer – usually call it FKM, and the brand “Viton” is also the name of this material sometimes. FKM is a seal material that has a very high heat resistance and is suitable for a wide range of chemicals. Other major advantages include resistance to aging and ozone, extremely low air permeability, and self-extinguishing of the material. The standard FKM material has excellent resistance to mineral oils and greases, aliphatic, aromatic, and chlorinated hydrocarbons, fuels, non-flammable hydraulic fluids (HFD), and many organic solvents and chemicals. Generally not heat resistant water, steam, polar solvents, alcohol-based brake fluid, and low molecular weight organic acids. But lots of FKM manufacturers have improved materials that can work at a temperature of -20°C to 230°C, that can work with hot water or steam applications. We have a quick coupling used in lots of carpet extractors brands, the o-ring has requested this type of FKM.
- FFKM – FFKM is perfluoro rubber compound, fluoride content is even higher than FKM material. They have improved their resistance to high temperatures and chemicals, and can even withstand the presence of oxygen plasma for hours. The maximum continuous service temperature for some grades is 327°C(621°F).
- Polytetrafluoroethylene – PTFE, is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. in quick couplings, the PTEF usually use as the Gaskets material in hydraulic oil application.
The Chemical Compatibility of Seal Materials
NBR materials are usually popular because of the lower cost and good performance on most fluids. They can work good at -40˚C to 110˚C and work at for most of the hydraulic oils.
NBR Seals are recommended for:
General Purpose Sealing
Petroleum Oils & Fluids
Silicone Greases & Oils
Di-Ester Base Lubricants
Ethylene Glycol Base Fluids
Ethylene Propylene Rubber (EPM) Seals for Quick Couplings
Probably the most versatile of all the seal materials, these seals feature a wide temperature range and are compatible across of a number of mediums.
FKM materials, the quick coupling manufacturers usually choose the Viton brand or the FFMK material, that can work in a better temperature of -20˚C to 230˚C. They usually will be an addtional options for the users.
FKM are recommended for
Phasphate Ester Base Hydraulic Fluids (Skydrol, Cellulube, Pydraul)
Steam (to 400 deg F)
Silicone Oils & Greases
Automotive Brake Fluids
Chloroprene Rubber (CR) or Neoprene Seals for Quick Disconnect Couplings