By March 15, 2023News

Aggressive pumping environments can be problematic for pump engineers. On the one hand it’s impossible to design the pump to be resistant to every kind of chemical, while on the other, the tendency is to either over specify a perfluoroelastomer to cover all eventualities or select a elastomer with mid-range chemical resistance in the hope this will cover most applications.

Picture of Fluoroelastomers Seals

Over recent years the elastomer industry has been systematically improving pump sealing performance – fine tuning temperature, chemical and mechanical properties in some areas and defining new benchmarks in others. As a result it has never been easier to match the seal to the pumping environment. The wide variety of sealing

options can, however, make it more difficult to select the correct seal; a case of too much choice, perhaps. With this in mind we offer the pump engineer a guide to recent development in fluoroelastomer technology.

Often referred to as FKM, fluoroelastomer seals are normally used in high temperature and aggressive fluid environments containing oils, aromatic hydrocarbons and

gasoline. They sit between Hydrogenated Nitrile Butadiene Rubber (HNBR) at the lower end in terms of their temperature and chemical resistance and perfluoroelastomers at the top end of the scale. Within the range of fluoroelastomers themselves, there are differences – so it is important to note that: Not all Fluoroelastomers Are The Same. The challenge to the pump engineer is understanding the options and variables involved in selecting an FKM sealing material.

Know your Fluoroelastomer

There are five main types of FKMs, determined by the types of monomers used to produce the fluoroelastomer as defined by ASTM D1418

. These include Vinylidene Fluoride (VF2), Hexafluoropropylene (HFP), Tetrafluoroethylene (TFE), Perfluoromethylvinylether (PMVE). The combination of monomers determines the properties of the FKM.

Type 1: VF2 + HFP (copolymer / dipolymer), bisphenol cured, good all-round properties and the most common FKM.

Type 2: VF2 + HFP + TFE (terpolymer), bisphenol cured, this elastomer has higher heat resistance and improved chemical resistance to aromatic and low molecular weight hydrocarbons over type 1 FKMs.

Type 3: VF2 + TFE + PMVE (terpolymer) peroxide cured, this elastomer widens the elastomer’s temperature capability enabling lower temperature flexibility. Older grades have a glass transition of -30°C while newer technology with longer ether containing pendent groups remains flexible to -40°C.


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