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Whereas in heating technology the functions are clearly defined, i.e., heating of the surroundings and supply of hot water, the boundaries in ventilation and air conditioning technology are more varied and the functions cannot always be clearly assigned. Essentially, they encompass control of air temperature, humidity and air quality (e.g. CO2 content) in a room in terms of required or desired parameters, plus potentially transporting fresh or treated air.
The diversity of the designs and functional principles of air conditioning systems and devices, and their applications (i.e., stationary, mobile/portable and on board of vehicles) is matched by the variety of requirements to be met by seals and sealing systems. The challenges here include both high and low temperatures, high operating pressures of up to 150 bar, and chemical resistance.
Parker Prädifa has developed specialty elastomer mixtures – CR, EPDM, NBR, HNBR and FKM compounds – optimally meeting requirements in a wide range of applications. Parker Prädifa additionally offers specialty seals for specific applications such as the “L-Seal” (a rubber-metal seal) for CO2 applications.
One Sealing Material for two Extremes
Seals in air conditioning systems must show very good high and low temperature behavior, i.e. flexibility and good mechanical properties at very low and very high temperatures. This is necessary because both extremes occur in the cooling circuit. Temperature differences of up to 140 °C (-40 °C to 100 °C) are not uncommon and dependent on the system’s design, range of application, and refrigerant.
Chemical Resistance against Refrigerants and Oils
Depending on their design and energy consumption, air conditioning systems use a wide variety of refrigerants that chemically interact with the sealing materials used in equally diverse ways. This poses special challenges such as solid-liquid extractions, where the refrigerant as a liquid extraction agent extracts substance components from the sealing compound.
The primary purposes served by refrigerant oils are lubrication of machine components, sealing within the compressor, and dissipation of the heat generated in the lubrication gap.
The bases on which refrigerant oils are produced vary. The most common ones are: mineral oil based, polyalphaolefins and polyglykols. Due to this variance, it is not possible to define and use a single sealing compound for the diverse types of refrigerant oils. The various additives in the oils pose a challenge as well.
Long-Term Setting Behavior for Long Service Life
Due to the longevity of service life as well as simple and extended maintenance intervals that air conditioning systems require, outstanding compression set of the seals and sealing materials is imperative.
Compression set refers to permanent deformation under certain conditions. Generally speaking: the better the compression set, i.e., the lower the permanent deformation in percent related to the deformation of the test piece, the higher the quality.
Compression set depends on the type of elastomer, mixture composition, processing conditions, test temperature and duration, deformation in percent, thickness of the test piece, and the test medium.
Sealing Materials for Air Conditioning Systems
Requirements to be met by the sealing components are uutstanding compression set, high extrusion resistance, minimal gas permeability, and resistance against explosive decompression, plus the previously mentioned extraction resistance of the material against the refrigerant.
For many standard applications, the chloroprene compound C0557 is used. Whenever higher or lower temperature resistance is needed, we can use EPDM, HNBR or FKM compounds.
Unfortunately, we cannot make any generally valid statements about resistance or suitability. Tests are required on a case-by-case basis. Please contact our application engineering team and we’ll be pleased to check your requirements profile and recommend the best material for your application.
Featured Sealing Solutions
EPDM O-Ring E8556
EPDM O-ring with focus on automotive, chemical processing, pharmaceutical and general industrial applications, black.
HNBR O-Ring N3831
HNBR O-ring with good mechanical robustness for automotive cooling systems, heavy duty, transportation, black.